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Prediction of discharge in a tidal river using the LSTM-based sequence-to-sequence models
Zhigao Chen, Yan Zong, Zihao Wu, Zhiyu Kuang, Shengping Wang
 doi: 10.1007/s13131-024-2343-6
[Abstract](63) [FullText HTML](29)
The complexity of river-tide interaction poses a significant challenge in predicting discharge in tidal rivers. Long short-term memory (LSTM) networks excel in processing and predicting crucial events with extended intervals and time delays in time series data. Additionally, the sequence-to-sequence (Seq2Seq) model, known for handling temporal relationships, adapting to variable-length sequences, effectively capturing historical information, and accommodating various influencing factors, emerges as a robust and flexible tool in discharge forecasting. In this study, we introduce the application of LSTM-based Seq2Seq models for the first time in forecasting the discharge of a tidal reach of the Changjiang River (Yangtze River) Estuary. This study focuses on discharge forecasting using three key input characteristics: flow velocity, water level, and discharge, which means the structure of multiple input and single output is adopted. The experiment used the discharge data of the whole year of 2020, of which the first 80% is used as the training set, and the last 20% is used as the test set. This means that the data covers different tidal cycles, which helps to test the forecasting effect of different models in different tidal cycles and different runoff. The experimental results indicate that the proposed models demonstrate advantages in long-term, mid-term, and short-term discharge forecasting. The Seq2Seq models improved by 6%–60% and 5%–20% of the relative standard deviation compared to the harmonic analysis models and improved Back Propagation (BP) neural network models in discharge prediction, respectively. In addition, the relative accuracy of the Seq2Seq model is 1% to 3% higher than that of the LSTM model. Analytical assessment of the prediction errors shows that the Seq2Seq models are insensitive to the forecast lead time and they can capture characteristic values such as maximum flood tide flow and maximum ebb tide flow in the tidal cycle well. This indicates the significance of the Seq2Seq models.
Preliminary study on the depositional model in the wave-dominated delta evolution during the Anthropocene: a case study of the Hanjiang River Delta in China
Hongyue Wang, Zhongbo Wang, Yang Wang, Haiyan Tang, Xiaodong Zhang, Xiaofeng Luo, Yongxin Mai, Xuhong Huang, Yilin Zheng, Ping Yin, Zhongping Lai
 doi: 10.1007/s13131-024-2313-z
[Abstract](29) [FullText HTML](12) [PDF 2924KB](0)
The deltas serve as the primary interactive zone where terrestrial and marine environments converge, playing a pivotal role in the coastal deposition. In the Holocene, climate changes and sea level fluctuation are the principal driving factors in the evolution of deltas. However, human activities such as the construction of dams and reservoirs in the Anthropocene have significantly altered sediment transport in rivers, leading to depositional pattern variation during deltaic evolution. In this study, we have conducted a comparative analysis of the morphological variations (1986–2021) in the barrier system of the Hanjiang River Delta (HRD) using satellite remote sensing (SRS) method. Additionally, we have examined the lithological changes and facies alterations observed in eight boreholes on the present barrier spit. Our findings indicate that the intensification of anthropogenic activities led to a significant reduction in the sediment flux of the Hanjiang River (HR), resulting in depocenter landward migration at the estuary. SRS analysis reveals their periodical morphological characteristics and spatial variations of estuarine sandbars (1986–1992), barrier islands-lagoons (1993–2009), and barrier spits (2010–2021) during 1986 to 2021. The stratigraphy of boreholes demonstrates a south-to-north facies transition from lagoon to lagoon-barrier spit and barrier spit in vertical lithology. Therefore, the depositional evolution of the HRD barrier system is categorized into three phases: estuarine sandbar-barrier island phase (1986–1998); barrier island-lagoon phase (1999–2009); and barrier spit phase (2010–2021). During the estuarine sandbar-barrier island phase, fluvial processes played a predominate role in the deposition. Consequently, with a significant decrease in river sediment load, the dominant factors driving depositional processes shifted towards wave action and alongshore current. Based on the conceptual model in the Holocene, we propose a modified depositional model of wave-dominated deltas during Anthropocene that encompasses three evolutionary phases: estuarine sandbars and delta front platforms, barrier island-lagoon formation and landward migration of barrier spits. This pattern highlights that human-induced reduction in river sediment flux has led to a seaward deltaic progradation driven by barrier landward migration.
Simulating the evolution of focused waves by a two-layer Boussinesq-type model
Ping Wang, Zhongbo Liu, Kezhao Fang, Wenfeng Zou, Xiangke Dong, Jiawen Sun
 doi: 10.1007/s13131-024-2321-z
[Abstract](34) [FullText HTML](14) [PDF 3124KB](1)
Accurate simulation of the evolution of freak waves by the wave phase focusing method requires accurate linear and nonlinear properties, especially in deep-water conditions. In this paper, we analyze the ability to simulate deep-water focused waves of a two-layer Boussinesq-type (BT) model, which has been shown to have excellent linear and nonlinear performance. To further improve the numerical accuracy and stability, the internal wave-generated method is introduced into the two-layer Boussinesq-type model. Firstly, the sensitivity of the numerical results to the grid resolution is analyzed to verify the convergence of the model; secondly, the focused wave propagating in two opposite directions is simulated to prove the symmetry of the numerical results and the feasibility of the internal wave-generated method; thirdly, the limiting focused wave condition is simulated to compare and analyze the wave surface and the horizontal velocity of the profile at the focusing position, which is in good agreement with the measured values. Meanwhile the simulation of focused waves in very deep waters agrees well with the measured values, which further demonstrates the capability of the two-layer BT model in simulating focused waves in deep waters.
Paleogene transgression process and environmental evolution in the deepwater area of the Baiyun Depression in the northern South China Sea
Peijun Qiao, Yuchi Cui, Qiong Ma, Qiang Yu, Lei Shao
 doi: 10.1007/s13131-024-2340-9
[Abstract](31) [FullText HTML](14)
Multiple borehole samples are collected from the Baiyun Depression in deep-water area of the northern South China Sea (SCS) in an effort to reconstruct transgression processes during the Paleogene based on palynalgal analysis. This study indicates that the Baiyun Depression generated a large group of palynopore assemblages and fluvial/lacustrine-related algae during the early and middle Eocene when the Wenchang Formation was deposited. The entire depression was dominated by fluvial and lacustrine facies before transgression. Its eastern and southeastern sags transitioned to shallow marine environment by generating a large abundance of marine dinoflagellates during the Enping deposition of the late Eocene. Meanwhile, the southern uplift zone simply yielded fluvial/lacustrine-related palynopores and algae, and was dominated by the fluvial and lacustrine environment during the early stage of the Enping Formation, prior to shifting into transitional setting in the later period. Northwestern sags remained extensive fluvial and delta facies without existence of marine dinoflagellates. It was until the depositional stage of the Zhuhai Formation (Oligocene) that the overall depression was strongly impacted from transgression process. Both eastern and southeastern sags were mainly under deep marine setting on a continental slope while northwestern and southern areas developed transitional facies. Although distribution and accumulation patterns varied greatly among sub-sags, the overall Baiyun Depression was characterized by widespread development of marine dinoflagellates. It should be noted that the northwestern sag also partly generated large-scale river delta deposits. Due to the eustatic rise and change of SCS spreading axis, the overall Baiyun Depression was mostly influenced by the deep marine environment on a continental slope during the early Miocene. Both northwestern sag and southern uplift zone were found plentiful marine dinoflagellates. In summary, transgression initiated from the eastern and southeastern Baiyun Depression before subsequently progressing into the farther west. Evolution of transgression process is also greatly consistent with the gradual westward expansion of the SCS.
Performance of Physical-informed Neural Network (PINN) for the key parameter inference in Langmuir turbulence parameterization scheme
Fangrui Xiu, Zengan Deng
 doi: 10.1007/s13131-024-2329-4
[Abstract](26) [FullText HTML](11)
The Stokes production coefficient (E6) constitutes a critical parameter within the Mellor-Yamada type (MY-type) Langmuir turbulence (LT) parameterization schemes, significantly affecting the simulation of turbulent kinetic energy, turbulent length scale, and vertical diffusivity coefficient for turbulent kinetic energy in the upper ocean. However, the accurate determination of its value remains a pressing scientific challenge. This study adopted an innovative approach by leveraging deep learning technology to address this challenge of inferring the E6. Through the integration of the information of the turbulent length scale equation into a Physical-informed Neural Network (PINN), we achieved an accurate and physically meaningful inference of E6. Multiple cases were examined to assess the feasibility of PINN in this task, revealing that under optimal settings, the average mean squared error of the E6 inference was only 0.01, attesting to the effectiveness of PINN. The optimal hyperparameter combination was identified using the Tanh activation function, along with a spatiotemporal sampling interval of 1 s and 0.1 m. This resulted in a substantial reduction in the average bias of the E6 inference, ranging from O(101) to O(102) times compared with other combinations. This study underscores the potential application of PINN in intricate marine environments, offering a novel and efficient method for optimizing MY-type LT parameterization schemes.
Quantitative analysis and prediction of the sound field convergence zone in mesoscale eddy environment based on data mining methods
Ming Li, Yuhang Liu, Yiyuan Sun, Kefeng Liu
 doi: 10.1007/s13131-024-2328-5
[Abstract](27) [FullText HTML](10)
The mesoscale eddy (ME) has a significant influence on the convergence effect in deep-sea acoustic propagation. Is there a certain mathematical relationship between the mesoscale eddy (ME) conditions and convergence zone (CZ) characteristics? This paper use statistical approaches to express quantitative relationships between the two. Based on the Gaussian vortex model, we construct various sound propagation scenarios under different eddy conditions, and carry out sound propagation experiments to obtain simulation samples. With a large number of samples, we first adopt the unified regression to set up analytic relationships between eddy conditions and CZ parameters. The sensitivity of eddy indicators to the CZ is quantitatively analyzed. Then, we adopt the machine learning (ML) algorithms to establish prediction models of CZ parameters by exploring the nonlinear relationships between multiple ME indicators and CZ parameters. Through the research, we can express the influence of ME on the CZ quantitatively, and achieve the rapid prediction of CZ parameters in ocean eddies. The prediction accuracy (R) of the CZ distance (mean R: 0.9815) is obviously better than that of the CZ width (mean R: 0.8728). Among the three ML algorithms, Gradient Boosting Decision Tree has the best prediction ability (root mean square error (RMSE): 0.136), followed by Random Forest (RMSE: 0.441) and Extreme Learning Machine (RMSE: 0.518).
Spatiotemporal features and vertical structures of four types of mesoscale eddies in the Kuroshio Extension region
Bowen Sun, Shuchang Xu, Zhankun Wang, Yujie Feng, Baofu Li
 doi: 10.1007/s13131-024-2323-x
[Abstract](33) [FullText HTML](16)
Except for conventional mesoscale eddies, there are also abundant warm cyclonic eddies (WCEs) and cold anticyclonic eddies (CAEs) in the global ocean. Based on the global mesoscale eddy trajectory atlas product, satellite altimetric and remote sensing datasets, and three-dimensional temperature/salinity dataset, spatiotemporal features of WCEs and CAEs are compared with traditional cold cyclonic eddies and warm anticyclonic eddies in the Kuroshio Extension (KE; 28°−43°N, 140°−170°E) region. Characteristics of abnormal eddies like radius, amplitude, eddy kinetic energy, and proportion in all eddies behave in significant asymmetry on the north and south sides of the KE jet. Unlike eddies in the general sense, temporal feature analysis reveals that it is more favorable to the formation and maintenance of WCEs and CAEs in summer and autumn, while winter is the opposite. The spatiotemporal variation of abnormal eddies is likely because the marine environment varying with time and space. Statistically, proportion of abnormal eddies increases rapidly in decaying stage during the whole eddy lifespan, resulting in smaller average radius, amplitude, sea surface temperature anomaly and sea surface height anomaly compared to normal ones. The three-dimensional composite structures for four types of eddies expose that the difference between abnormal and conventional eddies is not just limited to the sea surface, but also exists within the water below the sea surface. Vertical structures also indicate that the anomalous temperature signal is confined in the water from the sea surface to layers at about 30 m in the KE region.
Influence of lithospheric thickness distribution on oil and gas basins, China seas and adjacent areas
Jing Ma, Wanyin Wang, Hermann Zeyen, Yimi Zhang, Zhongsheng Li, Tao He, Dingding Wang
 doi: 10.1007/s13131-024-2342-7
[Abstract](54) [FullText HTML](25)
The distribution of oil and gas resources is intricately connected to the underlying structure of the lithosphere. Therefore, investigating the characteristics of lithospheric thickness and its correlation with oil and gas basins is highly important. This research utilizes recently enhanced geological–geophysical data, including topographic, geoid, rock layer thickness, variable rock layer density, and interface depth data. Employing the principles of lithospheric isostasy and heat conduction, we compute the laterally varying lithospheric thickness in the China seas and adjacent areas. From these results, two pivotal parameters for different types of oil and gas basins were statistically analyzed: the minimum lithospheric thickness and the relative fluctuation in lithospheric thickness. A semiquantitative analysis was used to explore the connection between these parameters and the hydrocarbon abundance within the oil and gas basins. This study unveils distinct variations in lithospheric thickness among basins, with oil and gas rich basins exhibiting a thicker lithosphere in the superimposed basins of central China and a thinner lithosphere in the rift basins of eastern China. Notably, the relative fluctuations in lithospheric thickness in basins demonstrate significant disparities: basins rich in oil and gas often exhibit greater thickness fluctuations. Additionally, in the offshore basins of China, a conspicuous negative linear correlation is observed between the minimum lithospheric thickness and the relative fluctuation in lithospheric thickness. This study posits that deep-seated thermal upwelling results in lithospheric undulations and extensional thinning in oil and gas basins. Concurrently, sustained deep-seated heat influences sedimentary materials in basins, creating favorable conditions for oil and gas generation. The insights derived from this study contribute to a quantitative understanding of the intricate relationships between deep lithospheric structures and oil and gas basins. These findings provide valuable guidance for future oil and gas exploration in the studied areas.
The sudden ocean warming and its potential influences on early−frozen landfast ice in Prydz Bay, East Antarctica
Haihan Hu, Jiechen Zhao, Jingkai Ma, Igor Bashmachnikov, Natalia Gnatiuk, Bo Xu, Fengming Hui
 doi: 10.1007/s13131-024-2326-7
[Abstract](28) [FullText HTML](12)
The ocean conditions beneath the ice cover play a key role in understanding the sea ice mass balance in the Polar Regions. An integrated high-frequency ice–ocean observation system, including Acoustic Doppler Velocimeter (ADV), Conductivity Temperature and Depth (CTD) Sensor, and Sea Ice Mass Balance Array (SIMBA), was deployed in the landfast ice region close to the Chinese Zhongshan Station in Antarctica. A sudden ocean warming of 0.14℃ (p < 0.01) was observed beneath early−frozen landfast ice, from (−1.60 ± 0.03)℃ during April 16–19 to (−1.46 ± 0.07)℃ during April 20–23, which is the only significant warming event in the nearly 8-month records. The sudden ocean warming brought a double rise in oceanic heat flux, from (21.7 ± 11.1) W/m2 during April 16–19 to (44.8 ± 21.3) W/m2 during April 20–23, which shifted the original growth phase at the ice bottom, leading to a 2 cm melting, as shown from SIMBA and borehole observations. Simultaneously, the slowdown of ice bottom freezing decreased salt rejection, and the daily trend of observed ocean salinity changed from +0.02/d during April 16–19, to +0.003/d during April 20–23. The potential reasons are increased air temperature due to the transit cyclones and the weakened vertical ocean mixing due to the tide phase transformation from semi-diurnal to diurnal. The high-frequency observations within the ice–ocean boundary layer enhance the comprehensive investigation of the ocean's influence on ice evolution at a daily scale.
Spatiotemporal characteristics of water exchange between the Andaman Sea and the Bay of Bengal
Yihao Wang, Feng Zhou, Xueming Zhu, Ruijie Ye, Yingyu Peng, Zhentao Hu, Haoran Tian, Na Li
 doi: 10.1007/s13131-024-2317-8
[Abstract](29) [FullText HTML](11)
A high-resolution customized numerical model is used to analyze the water transport in the three major water passages between the Andaman Sea and the Bay of Bengal, i.e., the Preparis Channel (PC), the Ten Degree Channel (TDC), and the Great Channel (GC), based on the daily averaged simulation results ranging from 2010 to 2019. Spectral analysis and EOF methods are employed to investigate the spatiotemporal variability of the water exchange and controlling mechanisms. The results of model simulation indicate that the net average transports of the PC and GC, as well as their linear trend, are opposite to that of the TDC. This indicates that the PC and the GC are the main inflow channels of the AS, while the TDC is the main outflow channel of the AS. The transport variability is most pronounced at surface levels and between 100 m and 200 m depth, likely affected by monsoons and circulation. A 182.4-d semiannual variability is consistently seen in all three channels, which is also evident in their second principal components. Based on sea level anomalies and Empirical Orthogonal Function (EOF) analysis results, this is primarily due to equatorial winds during the monsoon transition period, causing eastward movement of Kelvin waves along the Andaman Sea coast, thereby affecting the spatiotemporal characteristics of the flow in the Andaman Sea. The first EOF of the PC flow field section shows a split at 100 m, likely due to topography. The first EOF of the TDC flow field section is steady but has potent seasonal oscillations in its time series. Meanwhile, the first EOF of the GC flow field section indicates a stable surface inflow, probably influenced by the equatorial Indian Ocean’s eastward current.
An empirical method for joint inversion of wave and wind parameters based on SAR and wave spectrometer data
Yong Wan, Xiaona Zhang, Shuyan Lang, Ennan Ma, Yongshou Dai
 doi: 10.1007/s13131-024-2320-0
[Abstract](19) [FullText HTML](8)
Synthetic Aperture Radar (SAR) and wave spectrometers, crucial in microwave remote sensing, play an essential role in monitoring sea surface wind and wave conditions. However, they face inherent limitations in observing sea surface phenomena. SAR systems, for instance, are hindered by an azimuth cut-off phenomenon in sea surface wind field observation. Wave spectrometers, while unaffected by the azimuth cutoff phenomenon, struggle with low azimuth resolution, impacting the capture of detailed wave and wind field data.. This study utilizes SAR and Surface Wave Investigation and Monitoring (SWIM) data to initially extract key feature parameters, which are then prioritized using the Extreme Gradient Boosting (XGBoost) algorithm. The research further addresses feature collinearity through a combined analysis of feature importance and correlation, leading to the development of an inversion model for wave and wind parameters based on XGBoost. A comparative analysis of this model with ERA5 reanalysis and buoy data for of significant wave height, mean wave period, wind direction, and wind speed reveals root mean square errors of 0.212 m, 0.525 s, 27.446°, and 1.092 m/s, compared to 0.314 m, 0.888 s, 27.698°, and 1.315 m/s from buoy data, respectively. These results demonstrate the model’s effective retrieval of wave and wind parameters. Finally, the model, incorporating altimeter and scatterometer data, is evaluated against SAR/SWIM single and dual payload inversion methods across different wind speeds. This comparison highlights the model’s superior inversion accuracy over other methods.
Identification of the Caroline Plate Boundary: Constraints from Magnetic Anomaly
Yongtao Fu, Guoliang Zhang, Wanyin Wang, An Yang, Tao He, Zhangguo Zhou, Xiao Han
 doi: 10.1007/s13131-023-2272-9
[Abstract](38) [FullText HTML](15)
The Caroline Plate is located among the Pacific Plate, the Philippine Sea Plate, and the India Australia Plate, and plays a key role in controlling the spreading direction of the Philippine Sea Plate. The Caroline Submarine Plateau (or Caroline Ridge) and the Eauripik Rise on the south formed a remarkable T-shaped large igneous rock province, which covered the northern boundary between the Caroline Plate and the Pacific Plate. However, relationship between these tectonic units and magma evolution remains unclear. Based on magnetic data from the Earth Magnetic Anomaly Grid (2-arc-minute resolution) (V2), the normalized vertical derivative of the total horizontal derivative (NVDR-THDR) technique was used to study the boundary of the Caroline Plate. Results show that the northern boundary is a transform fault that runs 1400 km long in approximately 28 km wide along the N8° in E-W direction. The eastern boundary is an NNW-SSE trending fault zone and subduction zone with a width of tens to hundreds of kilometers; and the north of N4° is a fracture zone of dense faults. The southeastern boundary may be the Lyra Trough. The area between the southwestern part of the Caroline Plate and the Ayu Trough is occupied by a wide shear zone up to 100 km wide in nearly S-N trending in general. The Eauripik transform fault (ETF) in the center of the Caroline Plate and the fault zones in the east and west basins are mostly semi-parallel sinistral NNW-SSE–trending faults, which together with the eastern boundary Mussau Trench sinistral fault, the northern Caroline transform fault, and the southern shear zone of the western boundary, indicates the sinistral characteristics of the Caroline Plate. The Caroline hotspot erupted in the Pacific Plate near the Caroline transform fault and formed the West Caroline Ridge, and then joined with the Caroline transform fault at the N8°. A large amount of magma erupted along the Caroline transform fault, by which the East Caroline Ridge was formed. At the same time, a large amount of magma developed southward via the eastern branch of the ETF, forming the northern segment of the Eauripik Rise. Therefore, the magmatic activity of the T-shaped large igneous province is obviously related to the fault structure of the boundary faults between the Caroline Plate and Pacific Plate, and the active faults within the Caroline Plate.
Structural characteristics and tectonic division of the Zambezi Delta basin in the offshore East Africa: evidences from gravity and seismic data
Guozhang Fan, Wen Li, Liangbo Ding, Wanyin Wang, Hongping Wang, Dingding Wang, Lin Li, Hao Wang, Chaofeng Wang, Qingluan Wang, Ying Zhang
[Abstract](21) [FullText HTML](10)
The Zambezi Delta basin is a passive marginal basin located on the East African coast that has good oil and gas exploration potential. Due to the special geological evolutionary background of the Beira High in the Zambezi Delta basin, it has a low gravity anomaly, and the existing seismic survey lines do not cover the whole basin; therefore, it is difficult to interpret the structural characteristics of the whole basin based solely on gravity or seismic data. Based on satellite altimetry gravity anomaly data, this study infers the distribution characteristics of faults in the Zambezi Delta basin by using the normalized vertical derivative of the total horizontal derivative (NVDR-THDR) technique. Then, constrained by seismic data, the gravity anomaly at the Moho interface is extracted by using the fast forward method of the double-interface model of the gravity anomaly, and this anomaly is then removed from the Bouguer gravity anomaly to obtain the sedimentary layer gravity anomaly. The thickness of the sedimentary strata is obtained by inversing the sedimentary basement depth of the whole basin. Then, uplifts and depressions are divided based on a sedimentary layer thickness of 3 km. This research demonstrates that the Zambezi Delta basin mainly features nearly SN-trending and NE-trending faults and that these faults exhibit east‒west partitioning. The nearly SN-trending strike-slip faults controlled the sedimentary development of the basin, and the NE-trending tensile faults may have acted as migration channels for oil, gas and magma. The "overcompensation" effect of the Moho interface gravity anomaly on the gravity anomaly of the sedimentary layer is caused by the depression of the Moho interface beneath the Beira High, which results in a low gravity anomaly value for the Beira High. The pattern of uplifts and depressions trends NE and has the structural characteristics of east‒west blocks.
An ensemble learning method to retrieve sea ice roughness from Sentinel-1 SAR images
Pengyi Chen, Zhongbiao Chen, Runxia Sun, Yijun He
 doi: 10.1007/s13131-023-2248-9
[Abstract](161) [FullText HTML](74) [PDF 4034KB](8)
Sea ice surface roughness (SIR) affects the energy transfer between the atmosphere and the ocean, and it is also an important indicator for sea ice characteristics. To obtain a small-scale SIR with high spatial resolution, a novel method is proposed to retrieve SIR from Sentinel-1 synthetic aperture radar (SAR) images, utilizing an ensemble learning method. Firstly, the two-dimensional continuous wavelet transform is applied to obtain the spatial information of sea ice, including the scale and direction of ice patterns. Secondly, a model is developed using the Adaboost Regression model to establish a relationship among SIR, radar backscatter and the spatial information of sea ice. The proposed method is validated by using the SIR retrieved from SAR images and comparing it to the measurements obtained by the Airborne Topographic Mapper (ATM) in the summer Beaufort Sea. The determination of coefficient, mean absolute error, root-mean-square error and mean absolute percentage error of the testing data are 0.91, 1.71 cm, 2.82 cm, and 36.37%, respectively, which are reasonable. Moreover, K-fold cross-validation and learning curves are analyzed, which also demonstrate the method’s applicability in retrieving SIR from SAR images.
On the longitudinal shifts of the Agulhas retroflection point
Weiwei Zhang, Xiaoyi Yang, Wei Zhuang, Xiaohai Yan
 doi: 10.1007/s13131-023-2295-x
[Abstract](64) [FullText HTML](26) [PDF 4308KB](4)
The Agulhas system is the strongest western boundary current system in the Southern Hemisphere and plays an important role in modulating the Indian-to-Atlantic Ocean water exchange by the Agulhas leakage. It is difficult to measure in situ transport of the Agulhas leakage as well as the Agulhas retroflection position due to their intermittent nature. In this study, an innovative kinematic algorithm was designed and applied to the gridded altimeter observational data, to ascertain the longitudinal position of Agulhas retroflection, the stability of Agulhas jet stream, as well as its strength. The results show that the east-west shift of retroflection is related neither to the strength of Agulhas current nor to its stability. Further analysis uncovers the connection between the westward extension of Agulhas jet stream and an anomalous cyclonic circulation at its northern side, which is likely attributed to the local wind stress curl anomaly. To confirm the effect of local wind forcing on the east-west shift of retroflection, numerical sensitivity experiments were conducted. The results show that the local wind stress can induce a similar longitudinal shift of the retroflection as altimetry observations. Further statistical and case study indicates that whether an Agulhas ring can continuously migrate westward to the Atlantic Ocean or re-merge into the main flow depends on the retroflection position. Therefore, the westward retroflection may contribute to a stronger Agulhas leakage than the eastward retroflection.
Structural features in the mid-southern section of the Kyushu–Palau Ridge based on satellite altimetry gravity anomaly
Feifei Zhang, Dingding Wang, Xiaolin Ji, Fanghui Hou, Yuan Yang, Wanyin Wang
[Abstract](26) [FullText HTML](13)
The Kyushu–Palau Ridge (KPR), an anti-S-shaped submarine highland at the center of the Philippine Sea Plate (PSP), is considered the residual arc of the Izu–Bonin–Mariana Island Arc, which retains key information about the cessation of the Western Philippine Basin (WPB) expansion and the Parece Vela Basin (PVB) breakup. Herin, using the new generation of satellite altimetry gravity data, high-precision seafloor topography data, and newly acquired ship-borne gravity data, the topographic and gravity characteristics of the KPR mid-southern section and adjacent region are depicted. The distribution characteristics of the faults were delineated using the total horizontal derivative (NVDR-THDR) method normalized vertical derivative and the minimum curvature potential field separation method. The Moho depth and crustal thickness were inverted using the rapid inversion method for a double-interface model with depth constraints. Based on these results, the crust structure features in the KPR mid-southern section, and the “triangular” structure geological significance where the KPR and Central Basin Rift (CBR) of the WPB intersect are interpreted. The KPR crustal thickness is approximately 6–16 km, with a distinct discontinuity that is slightly thicker than the normal oceanic crust. The KPR mid-southern section crust structure was divided into four segments (S1–S4) from north to south, formed by the CBR eastward extension joint action and clockwise rotation of the PVB expansion axis and the Mindanao fault zone blocking effect.
Study on crustal thickness and the prediction of prolific depressions: the Bohai Basin as an example
Mengke Cai, Gongcheng Zhang, Wanyin Wang, Dingding Wang
[Abstract](31) [FullText HTML](16)
The deep crustal structure is closely related to oil and gas reserves. Predicting the oil and gas enrichment of depressions based on the Moho depth and crustal thickness is a promising research topic with significant implications for guiding exploration in petroliferous basins. In this study, seismic data were used as a constraint on the use of satellite gravity anomaly inversion to obtain the distribution of Moho depth and crustal thickness in the Bohai Basin. Stretching factors were calculated to analyze the differential distribution of deep crustal structural activity. Four indicators, including the minimum Moho depth, minimum crustal thickness, sum of Moho stretching factors, and sum of crustal stretching factors, were selected. Principal component analysis was applied to reduce the dimensionality of the multi-indicator system and obtain an oil and gas enrichment score for quantitative prediction of favorable prolific depressions. The deviation between the inverted Moho depth and seismic constraints was small; thus, the data effectively reflect the variations in the characteristics of each depression. The analysis revealed significant statistical features related to the minimum Moho depth/crustal thickness and the sum of Moho/crustal stretching factors associated with prolific depressions. Based on the oil and gas enrichment score, the depressions were classified into four categories related to their different deep crustal structural characteristics. Highly active Class I, Class II, and Class III depressions are predicted to be favorable prolific depressions. This study expands the research on quantitatively predicting favorable prolific depressions in the Bohai Basin using the deep crustal structure and can contribute to reducing production costs and improving exploration efficiency in future explorations.
An improved wind quality control for the China-France Oceanography Satellite (CFOSAT) scatterometer
Xiaoheng Mou, Wenming Lin
 doi: 10.1007/s13131-024-2322-y
[Abstract](49) [FullText HTML](20)
Quality control (QC) is an essential procedure in scatterometer wind retrieval, which is used to distinguish good-quality data from poor-quality wind vector cells (WVCs) for the sake of wind applications. The current wind processor of the China France Oceanography Satellite (CFOSAT) scatterometer (CSCAT) adopts a maximum likelihood estimator (MLE)-based QC method to filter WVCs affected by geophysical noise, such as rainfall and wind variability. As the first Ku-band rotating fan-beam scatterometer, CSCAT can acquire up to 16 observations over a single WVC, giving abundant information with diverse incidence/azimuth angles, as such its MLE statistical characteristics may be different from the previous scatterometers. In this study, several QC indicators, including MLE, its spatially averaged value (MLEm), and the singularity Exponents (SE), are analyzed using the collocated Global Precipitation Mission (GPM) rainfall data as well as buoy data, to compare their sensitivity to rainfall and wind quality. The results show that wind error characteristics of CSCAT under different QC methods are similar to those of other Ku-band scatterometers, i.e., SE is more suitable than other parameters for the wind QC at outer-swath and nadir regions, while MLEm is the best QC indicator for the sweet region WVCs. Specifically, SE is much more favorable than others at high wind speeds. By combining different indicators, an improved QC method is developed for CSCAT. The validation with the collocated buoy data shows that it accepts more WVCs, and in turn, improves the quality control of CSCAT wind data.
Temporal variations of food web in a marine bay ecosystem based on LIM-MCMC model
Pengcheng Li, Hu Zhang, Chongliang Zhang, Binduo Xu, Yupeng Ji, Yiping Ren, Ying Xue
 doi: 10.1007/s13131-023-2273-8
[Abstract](48) [FullText HTML](22)
Climate change has led to significant fluctuations in marine ecosystems, including alterations in the structure and function of food webs and ecosystem status. Coastal ecosystems are critical to the functioning of the earth’s life-supporting systems. However, temporal variations in most of these ecosystems have remained unclear so far. In this study, we employed a linear inverse model with Markov Chain Monte Carlo (LIM-MCMC) combined with ecological network analysis (ENA) to reveal the temporal variations of the food web in Haizhou Bay of China. Food webs were constructed based on diet composition data in this ecosystem during the year of 2011 and 2018. Results indicated that there were obvious temporal variations in the composition of food webs in autumn of 2011 and 2018. The number of prey and predators for most species in food web decreased in 2018 compared with 2011, especially for Trichiurus lepturus, zooplankton, Amblychaeturichthys hexanema, and Loligo sp. ENA showed that the complexity of food web structure could be reflected by comprehensive analysis of compartmentalized indicators. Haizhou Bay ecosystem was more mature and stable in 2011, while the ecosystem’s self-sustainability and recovery from disturbances were accelerated from 2011 to 2018. These findings contribute to our understanding of the dynamics of marine ecosystems and highlight the importance of comprehensive analysis of marine food webs. This work provides a framework for assessing and comparing temporal variations in marine ecosystems, which provides essential information and scientific guidance for the Ecosystem-based Fisheries Management (EBFM).
Three-dimensional thermohaline structure estimation derived from HY-2 satellite data over the Maritime Silk Road and its applications
Zhiqiang Chen, Xidong Wang, Xiangyu Wu, Yuan Cao, Zikang He, Dakui Wang, Jian Chen
 doi: 10.1007/s13131-023-2299-6
[Abstract](65) [FullText HTML](27)
Estimated ocean subsurface fields derived from satellite observations provide potential data sources for operational marine environmental monitoring and prediction systems. This study employs a statistic regression reconstruction method, in combination with domestic autonomous sea surface height and sea surface temperature observations from the Haiyang-2 (HY-2) satellite fusion data, to establish an operational quasi-real-time three-dimensional (3D) temperature and salinity products over the Maritime Silk Road Sea. These products feature a daily temporal resolution and a spatial resolution of 0.25° × 0.25° and exhibit stability and continuity. We have demonstrated the accuracy of the reconstructed thermohaline fields in capturing the 3D thermohaline variations through comprehensive statistical evaluations, after comparing them against Argo observations and ocean analysis data from 2022. The results illustrate that the reconstructed fields effectively represent seasonal variations in oceanic subsurface structures, along with structural changes resulting from mesoscale processes, and the upper ocean’s responses to tropical cyclones. Furthermore, the incorporation of HY-2 satellite observations notably enhances the accuracy of temperature and salinity reconstructions in the Northwest Pacific Ocean and marginally improves salinity reconstruction accuracy in the North Indian Ocean when compared to the World Ocean Atlas 2018 monthly climatology thermohaline fields. As a result, the reconstructed product holds promise for providing quasi-real-time 3D temperature and salinity field information to facilitate fast decision-making during emergencies, and also offers foundational thermohaline fields for operational ocean reanalysis and forecasting systems. These contributions enhance the safety and stability of ocean subsurface activities and navigation.
Tomographic inversion of OBS converted shear waves: Case study of profile EW6 in the Dongsha area
Genggeng Wen, Kuiyuan Wan, Shaohong Xia, Xiuwei Ye, Huilong Xu, Chaoyan Fan, Jinghe Cao, Shunshan Xu
[Abstract](31) [FullText HTML](17)
Studies of converted S-wave data recorded on the Ocean Bottom Seismometer (OBS) allow for the estimation of crustal S-wave velocity, from which is further derived the Vp/Vs ratio to constrain the crustal lithology and geophysical properties. Constructing a precise S-wave velocity model is important for deep structural research, and inversion of converted S-waves provides a potential solution. However, the inversion of the converted S-wave remains a weakness because of the complexity of the seismic ray path and the inconsistent conversion interface. In this study, we introduced two travel time correction methods for the S-wave velocity inversion and imaged different S-wave velocity structures in accordance with the corresponding corrected S-wave phases using seismic data of profile EW6 in the northeastern South China Sea (SCS). The two inversion models show a similar trend in velocities, and the velocity difference is < 0.15 km/s (mostly in the range of 0–0.1 km/s), indicating the accuracy of the two travel time correction methods and the reliability of the inversion results. According to simulations of seismic ray tracing based on different models, the velocity of sediments is the primary influencing factor in ray tracing for S-wave phases. If the sedimentary layer has high velocities, the near offset crustal S-wave refractions cannot be traced. In contrast, the ray tracing of Moho S-wave reflections was not significantly impacted by the velocity of the sediments. The two travel time correction methods have their own advantages, and the application of different approaches is based on additional requirements. These works provide an important reference for future improvements in converted S-wave research.
Astronomical Influence of the Development of Paleogene Thin Coal Seam Groups in Offshore Lacustrine Basins: A Case Study of the Zhu Ⅰ Depression’s Enping Formation Located in the Northern Section of the South China Sea
Liu Yan, Huang Shengbing, WANG Dongdong, Li Nan, Yin Yuting, Chen Ying, Li Zengxue
[Abstract](37) [FullText HTML](19)
The development of the Paleogene coal seams in China's offshore basin areas generally had the characteristics of coal measures with large thicknesses, large numbers of coal seams, thin single coal seams, poor stability, scattered vertical distribution, and a wide distribution range. This study selected the Enping Formation of the Zhu I Depression in the northern section of the South China Sea as an example to determine the macro-control factors of the development of the Paleogene coal seam groups. An analysis was carried out on the influencing effects and patterns of the astronomical cycles related to the development of the thin coal seam groups in the region. A floating astronomical time scale of the Enping Formation was established, and the sedimentary time limit of the Enping Formation was determined to be approximately 6.15 Ma±. In addition, the cyclostratigraphy analysis results of the natural gamma-ray data of Well XJ in the Enping Formation of the Xijiang Sag revealed that the development of the thin coal seams had probably been affected by short eccentricity and precession factors. The formation process of coal seams was determined to have been affected by high seasonal contrast, precipitation, and insolation. During the periods with high values of short eccentricity, the seasonal contrasts tended to be high. During those periods, fluctuations in the precession controls resulted in periodic volume changes in precipitation and insolation of the region, resulting in the development of thin coal seams. It was also found that the periods with low precession were the most conducive to coal seam development. On that basis, combined with such factors as sedimentary environmental conditions conducive to the development of thin coal seam groups, this study established a theoretical model of the comprehensive influences of short eccentricity and precession on the development and distribution of Paleogene thin coal seam groups in offshore lacustrine basins. The patterns of the Paleogene astronomical periods and paleoclimate evolution, along with the control factors which impacted the development of thin coal seam groups in offshore lacustrine basins, were revealed.
Acoustical imaging of the nearshore seafloor depositions and deformations, a key study for Western Istanbul, Türkiye
ÖZGAN Sinan, ALP Hakan, BAYAT Oğuz, VARDAR Denizhan
 doi: 10.1007/s13131-023-2197-3
[Abstract](171) [FullText HTML](82)
To protect the sustainability of the benefits from seas and near coastal areas, which have under the effect of the very complex hydrodynamic conditions and intensive human activities, without disrupting the balance of nature, it is necessary to image the status of the seafloor features. Therefore, this study presents the deformations, depositional conditions, underwater constructions, and the other non-natural impacts on the seafloor of the nearshore area at western Istanbul (between Küçükçekmece and Büyükçekmece Lagoons) where it intensely used by the citizens. The results of the study may provide some guidance for understanding the impacts and risk factors of uses that are or will be conducted in coastal and/or near-coastal areas. Construction planning for civil coastal structures and areas should be done in great harmony with nature, minimizing negative environmental impacts. Although sediment distribution in the area is generally quite complex, the current state of the region, wave action, hydrodynamic conditions, the amount of material transported from the land, and bathymetry are important influencing factors. The seafloor has been damaged primarily by anchor deformation and associated bottom scanning, as well as disturbing trawl tracks. The seafloor was observed as partially shallowing near the constructions (such as natural gas pipelines, fishermen's shelter, and port piles) of coastal areas and associated with sand deposits. Therefore, scanning the seafloor using side-scan sonar may provide valuable frequency data to prevent future disruptions.
An innovative classification system for ranking the biological effects of marine aromatic hydrocarbons based on fish embryotoxicity
RongHui Zheng, Chao Fang, FuKun Hong, Min Zhang, Fulong Gao, YuSheng Zhang, Jun Bo
 doi: 10.1007/s13131-023-2245-z
[Abstract](42) [FullText HTML](16)
Petroleum hydrocarbon pollution is a global concern, particularly in coastal environments. Polycyclic aromatic hydrocarbons (PAHs) are regarded as the most toxic components of petroleum hydrocarbons. In this study, the biomonitoring and ranking effects of petroleum hydrocarbons and PAHs on the marine fish model Oryzias melastigma embryos were determined in the Jiulong River Estuary (JRE) and its adjacent waters in China. The results showed that the levels of petroleum hydrocarbons from almost all sites met the primary standard for marine seawater quality, and the concentrations of the 16 priority PAHs in the surface seawaters were lower compared with those in other coastal areas worldwide. A new fish expert system based on the embryotoxicity of O. melastigma (OME-FES) was developed and applied in the field to evaluate the biological effects of petroleum hydrocarbons and PAHs. The selected physiological index and molecular indicators in OME-FES were appropriate biomarkers for indicating the harmful effects of petroleum hydrocarbons and PAHs. The outcome of OME-FES revealed that the biological effect levels of the sampling sites ranged from level I (no stress) to level III (medium stress), which is further corroborated by the findings of nested analysis of variance (ANOVA) models. Our results suggest that the OME-FES is an effective tool for evaluating and ranking the biological effects of marine petroleum hydrocarbons and PAHs. This method may also be applied to evaluate other marine pollutants based on its framework.
Effects of nutrient limitations on the sinking velocity of Thalassiosira weissflogii
Jie Zhu, Qiang Hao, Wei Zhang, Yingying Ma, Jiangning Zeng
 doi: 10.1007/s13131-024-2309-8
[Abstract](44) [FullText HTML](17)
The sinking of diatoms is critical to the formation of oceanic biological pumps and coastal hypoxic zones. However, little is known about the effects of different nutrient restrictions on diatom sinking. In this study, we measured the sinking velocity (SV) of Thalassiosira weissflogii using a new phytoplankton video observation instrument and analyzed major biochemical components under varying nutrient conditions. Our results showed that the SV of T. weissflogii under different nutrient limitation conditions varied substantially. The highest SV of (1.77 ± 0.02) m/d was obtained under nitrate limitation, significantly surpassing that under phosphate limitation at (0.98 ± 0.13) m/d. As the nutrient limitation was released, the SV steadily decreased to (0.32 ± 0.03) m/d and (0.15 ± 0.05) m/d, respectively. Notably, under conditions with limited nitrate and phosphate concentrations, the SV values of T. weissflogii significantly positively correlated with the lipid content (P < 0.001), with R2 values of 0.86 and 0.69, respectively. The change of the phytoplankton SV was primarily related to the intracellular composition, which is controlled by nutrient conditions but did not significantly correlate with transparent extracellular polymer and biosilica contents. The results of this study help to understand the regulation of the vertical sinking process of diatoms by nutrient restriction and provide new insights into phytoplankton dynamics and their relationship with the marine nutrient structure.
Effect of dissolved organic nitrogen on the bloom of Prorocentrum donghaiense and Karenia spp. in the East China Sea coastal waters
Xiaoru Cui, Guangming Zhen, Jing Zhao, Keqiang Li, Xiulin Wang
 doi: 10.1007/s13131-023-2308-9
[Abstract](48) [FullText HTML](16)
Understanding the mechanism of harmful algal bloom formation is vital for effectively preventing algal bloom outbreaks in coastal environments. Karenia spp. blooms in the East China Sea show a significant correlation with nutrient regimes. However, the impact of key components of nutrients, especially dissolved organic nitrogen (DON), on the blooms of Karenia spp. is not clear. Quantitative research is still lacking. In this study, the cruise observations, field mesocosm-flask culture experiments, and a multinitrogen-tri-phytoplankton-detritus model (NTPD) are combined to reveal the quantitative influence of nutrient regimes on the shift of Prorocentrum donghaiense (P. donghaiense) and Karenia spp. in the East China Sea. It has a synchronism rhythm of diatom-P. donghaiense-Karenia spp.-diatom loop in the field culture experiment, which is consistent with the results of the cruise observation. The results showed that the processes of Terrigenous DON (TeDON) and dissolved inorganic nitrogen (DIN: NO3-N, NH4-N) absorption promoted P. donghaiense to become the dominant algae in the community; whereas the processes of DON from P. donghaiense absorption promoted Karenia app. to become the dominant algae in ambient DIN exhaustion. In addition, the three-dimensional fluorescence components of humus C, tyrosine and fulvic acid can indicate the processes of growth and extinction of P. donghaiense and Karenia spp., respectively. This study infers that P. donghaiense and Karenia spp. regime shift mechanism associated with the nutrient regime in coastal waters, which provides a scientific basis for the environmental management of coastal ecosystem health.
Coastal hypoxia response to the coupling of catastrophic flood, extreme marine heatwave and typhoon: a case study off the Changjiang Estuary in summer 2020
Xiao Ma, Qicheng Meng, Dewang Li, Yuanli Zhu, Xiaobo Ni, Dingyong Zeng, Di Tian, Ting Huang, Zhihao Jiang, Haiyan Jin, Feng Zhou
 doi: 10.1007/s13131-024-2311-1
[Abstract](45) [FullText HTML](14)
Massive bodies of low-oxygen bottom waters are found in coastal areas worldwide, which are detrimental to coastal ecosystems. In summer 2020, the response of coastal hypoxia to extreme weather events, including a catastrophic flooding, an extreme marine heatwave, and typhoon Bavi, is investigated based on multiple satellite, four cruises, and mooring observations. The extensive fan-shaped hypoxia zone presents significant northward extension during July−September 2020, and is estimated as large as 13 000 km2 with rather low oxygen minimum (0.42 mg/L) during its peak in 28−30 August. This severe hypoxia is attributed to the persistent strong stratification, which is indicated by flood-induced larger amount of riverine freshwater input and subsequent marine heatwave off the Changjiang Estuary. Moreover, the typhoon Bavi has limited effect on the marine heatwave and coastal hypoxia in summer 2020.
Formation environment and hydrocarbon potential of the Paleogene Enping Formation coal measures in the Zhu I Depression of South China Sea
Yuting Yin, Lei Lan, Dongdong Wang, Ying Chen, Yan Liu, Youchuan Li, Zengxue Li, Jiamin Liu
[Abstract](34) [FullText HTML](16)
The coal-measure source rock in the Chinese Sea area plays a significant role as a hydrocarbon source rock, with its genetic environment, development and distribution, and hydrocarbon generation potential serving as essential factors for the exploration of coal-type oil and gas fields. This study focuses on the coal-measure source rock of the Paleogene Enping Formation in the Zhu I Depression, located in the northern South China Sea. The main geological insights obtained are as follows. The coal measures of the Enping Formation are developed in a warm and wet tropical-subtropical climate. The development environment of the coal-measure source rock in the Enping Formation includes the braided river delta upper plain peat swamp, characterized by dry forest swamp coal facies with relatively thick coal seams and a small number of layers. The braided river delta lower plain swamp-interdistributary bay of braided river delta front represents a forest edge-wetland herbaceous swamp coal facies with numerous layers of thin coal seams and poor stability. The shore swamp corresponds to an open water swamp coal facies with multiple layers of thin coal seams and poor stability. The organic matter abundance in the braided river delta upper plain is the highest, followed by the braided river delta lower plain-braided river delta front, and the shore-shallow lake. The organic matter type is predominantly type II1. Thermal evolution analysis suggests that the organic matter has progressed into a substantial oil generation stage. The hydrocarbon generation potential of the coal-measure source rock in the Enping Formation is the highest in the braided river delta upper plain, followed by the braided river delta lower plain-braided river delta front and the shore-shallow lake. Overall, this study proposes three organic facies in the coal-measure source rock of the Enping Formation: upper-plain swamp-dry forest swamp facies, lower plain-interdistributary bay-forest-herbaceous swamp facies, and lake swamp-herbaceous swamp facies.
Thiosulfate oxidation and autotrophy potential by marine prevalent heterotrophic bacteria of genus Marinobacter
Fei Xu, Xiang Zeng, Yadong Gong, Zongze Shao
[Abstract](26) [FullText HTML](12)
The genus Marinobacter is very broadly distributed in global environments and is considered as aerobic heterotroph. In this study, six Marinobacter strains were identified with autotrophic thiosulfate oxidation capacity. These strains, namely Marinobacter guineae M3BT, Marinobacter aromaticivorans D15-8PT, Marinobacter vulgaris F01T, Marinobacter profundi PWS21T, Marinobacter denitrificans JB02H27T, and Marinobacter sp. ST-1M (with a 99.93 % similarity to the 16S rDNA sequences of Marinobacter salsuginis SD-14BT), were screened out of 32 Marinobacter strains by autotrophic thiosulfate oxidization medium. The population of cells grew in a chemolithotrophic medium, increasing from 105 to 107 cells /mL within 5 days. This growth was accompanied by the consumption of thiosulfate 3.59 mM to 9.64 mM and the accumulation of sulfate up to 0.96 mM, and occasionally produced sulfur containing complex particles. Among these Marinobacter strains, it was also found their capability of oxidizing thiosulfate to sulfate in a heterotrophic medium. Notably, M. vulgaris F01T and M. antarcticus ZS2-30T showed highly significant production of sulfate at 9.45 mM and 3.10 mM. Genome annotation indicated that these Marinobacter strains possess a complete Sox cluster for thiosulfate oxidation. Further phylogenetic analysis of the soxB gene revealed that six Marinobacter strains formed a separate lineage within Gammaproteobacteria and close to obligate chemolithoautotroph Thiomicrorhabdus arctica. The results indicated that thiosulfate oxidizing and chemolithoautotrophic potential in Marinobacter genus, which may contribute to the widespread of Marinobacter in the global ocean.
A numerical model study on the spatial and temporal variabilities of dissolved oxygen in Qinzhou Bay of the northern Beibu Gulf
Gaolei Cheng, Shiqiu Peng, Bin Yang, Dongliang Lu
 doi: 10.1007/s13131-023-2243-1
[Abstract](40) [FullText HTML](17)
Oxygen facilitates the breakdown of the organic material to provide energy for life. The concentration of dissolved oxygen (DO) in the water must exceed a certain threshold to support the normal metabolism of marine organisms. Located in the northern Beibu Gulf, Qinzhou Bay receives abundant freshwater and nutrients from several rivers which significantly influence the level ofthe dissolved oxygen. However, the spatial-temporal variations of DO as well as the associated driving mechanisms have been rarely studiedstudied through field observations. In this study, a three-dimensional coupled physical-biogeochemical model is used to investigate the spatial and seasonal variations of the DO and the associated driving mechanisms in Qinzhou Bay. The validation against observations indicates that the model can capture the seasonal and inter-annual variability of the DO concentration with the range of 5−10 mg·L−1. Sensitivity experiments show that the river discharges, winds and tides play crucial roles in the seasonal variability of the DO by changing the vertical mixing and stratification of the water column and the circulation pattern. In winter, the tide and wind forces have strong effects on the DO distribution by enhancing the vertical mixing, especially near the bay mouth. In summer, the river discharges play a dominant role in the DO distribution by inhibiting the vertical water exchange and delivering more nutrients to the Bay, which increases the DO depletion and results in lower DO on the bottom of the estuary salt wedge. These findings can contribute to the preservation and management of the coastal environment in the northern Beibu Gulf.
The Middle Miocene lobe-shaped and band-shaped submarine fans in the Lingshui Sag, Qiongdongnan Basin: source-to-sink system, genesis and implication
Xingzong Yao, Congjun Feng, Hongjun Qu, Min Zhang, Daming Li
[Abstract](43) [FullText HTML](23)
Deepwater oil and gas exploration is the key to sustainable breakthroughs in petroleum exploration worldwide. The Central Canyon gas field has confirmed the Lingshui Sag is a hydrocarbon-generating sag, and the deepwater reservoirs in the Lingshui Sag still have more fabulous oil and gas exploration potential. Based on drilling data and three-dimensional (3D) seismic data, this paper uses seismic facies analysis, seismic attribute analysis, and coherence slice analysis to identify the types of submarine fans (lobe-shaped and band-shaped submarine fans) that developed in the Lingshui Sag during the Middle Miocene, clarify the source-to-sink system of the submarine fans and discuss the genesis mechanism of the submarine fans. The results show that: (1) the deepwater source-to-sink system of the Lingshui Sag in the Middle Miocene mainly consisted of a “delta (sediment supply) - submarine canyon (sediment transport channel) - submarine fan (deepwater sediment sink)” association; (2) the main factor controlling the formation of the submarine fans developed in the Lingshui Sag was on the relative sea level decline; and (3) the bottom current reworked the lobe-shaped submarine fan that developed in the northern Lingshui Sag and formed the band-shaped submarine fan with a greater sand thickness. This paper aims to provide practical geological knowledge for subsequent petroleum exploration and development in the deepwater area of the Qiongdongnan Basin through a detailed analysis of the Middle Miocene submarine fan sedimentary system developed in the Lingshui Sag.
Impacts of Early Pleistocene glacial vicariance among refugial lineages and Mid-Late Pleistocene interglacial dispersal and expansion on forging population genetic structure of the giant clam Tridacna squamosa (Bivalvia: Cardiidae: Tridacninae) across the Red Sea and Indo-West Pacific Oceans
Temim Deli
[Abstract](42) [FullText HTML](22)
This study aims at identifying the microevolutionary processes responsible for the onset of the remarkable phylogeographic structure already recorded for the endangered giant clam Tridacna squamosa across its distribution range. For this purpose, the evolutionary, biogeographic and demographic histories of the species were comprehensively reconstructed in a mitochondrial dataset comprising nearly the whole available published cytochrome c oxidase 1 gene sequences of T. squamosa. Relatively higher level of genetic diversification was unveiled within T. squamosa, in comparison to earlier macro-geographic investigations, whereby five mitochondrial clusters were delineated. The resulting divergent gene pools in the Red Sea, Western Indian Ocean, Indo-Malay Archipelago and Western Pacific were found to be driven by Early Pleistocene glacial vicariance events among refugial lineages. Accentuated genetic diversification of the species across the Indo-Malay Archipelago was successively triggered by historical dispersal event during the Mid-Pleistocene MIS19c interglacial. This latter historical event might have also enabled genetically distinct giant clams from the Indo-Malay Archipelago to subsequently colonize the Western Pacific, accounting for the genetic diversity hotspot detected within this region (comprising three divergent mitochondrial clusters). Late Pleistocene demographic expansion of T. squamosa, during the Last Interglacial period, could have contributed to forging spatial distribution of the so far delineated genetic entities across the Indo-Western Pacific. Overall, being resilient to major climate shifts during the Pleistocene through adaptation and consequent diversification, T. squamosa could be used as a model species to track the impact of climate change on genetic variability and structure of marine species. In particular, the new information, provided in this investigation, may help with understanding and/or predicting the consequences of ongoing global warming on genetic polymorphism of endangered coral reef species among which Tridacna sp. are listed as ecologically important.
Diatoms as indicators of environmental change in coastal areas: a case study in Lianjiang, East China Sea
Tong Li, Jihui Zhang, Dongling Li, Chengxu Zhou, Chenxi Liu, Hao Xu, Bing Song, Longbin Sha
[Abstract](83) [FullText HTML](41)
Owing to the significant differences in environmental characteristics and explanatory factors among estuarine and coastal regions, research on diatom transfer functions and database establishment remains incomplete. This study analysed diatoms in surface sediment samples and a sediment core from the Lianjiang coast of the East China Sea, together with environmental variables. Principal component analysis of the environmental variables showed that sea surface salinity (SSS) and sea surface temperature were the most important factors controlling hydrological conditions in the Lianjiang coastal area, whereas canonical correspondence analysis indicated that SSS and pH were the main environmental factors affecting diatom distribution. Based on the modern diatom species–environmental variable database, we developed a diatom-based SSS transfer function to quantitatively reconstruct the variability in SSS between 1984 and 2021 for sediment core HK3 from the Lianjiang coastal area. The agreement between the reconstructed SSS and instrument SSS data from 1984–2021 suggests that diatom-based SSS reconstruction is reliable for studying past SSS variability in the Lianjiang coastal area. Three low SSS events in AD 2019, 2013, and 1999, together with an increased relative concentration of freshwater diatom species and coarser sediment grain sizes, corresponded to two super-typhoon events and a catastrophic flooding event in Lianjiang County. Thus, a diatom-based SSS transfer function for reconstructing past SSS variability in the estuarine and coastal areas of the East China Sea can be further used to reflect the paleoenvironmental events in this region.
Frequent recombination in Cynoglossus abbreviatus (Pleuronectiformes: Cynoglossidae) ribosomal 18S rDNA
Li Gong, Tingqi Jiang, Bilin Hu, Kaixin Wang, Nannan Zhang, Zengliang Miao
[Abstract](61) [FullText HTML](31)
The conventional theory of concerted evolution has been used to explain the lack of sequence variation in ribosomal RNA (rRNA) genes across diverse eukaryotic species. However, recent investigations into rRNA genes in flatfish genome have resulted in controversial findings. This study focuses on 18S rRNA genes of the widely distributed tongue sole, Cynoglossus abbreviatus (Pleuronectiformes: Cynoglossidae), aiming to explore sequence polymorphism. Five distinct 18S rDNA sequence types (Type A, B, R1, R2, and R3) were identified, suggesting a departure from concerted evolution. A combination of general criteria and variations in highly conserved regions were employed to detect pseudogenes. The results pinpointed Type A sequences as potential pseudogenes due to significant sequence variations and deviations in secondary structure within highly conserved regions. Three types (Type R1, R2, and R3) were identified as recombinants between Type A and B sequences, with simple crossing over and gene conversion as the most likely recombination mechanisms. These findings not only contribute to rRNA pseudogene identification but also shed light on the evolutionary dynamics of rRNA genes in teleost genomes.
A Review on the parasitic isopod genus Notophryxus G O Sars, 1883 (Crustacea: Isopoda), and first report of Notophryxus globularis G O Sars, 1885 from Lakshadweep Sea (Amini Island)
Mukkattu Nazar Suhaana, Jaime Gómez-Gutiérrez, Paravanparambil Rajakumar Jayachandran, Punnakkal Hari Praved, Sivasankaran Bijoy Nandan
 doi: 10.1007/s13131-023-2217-3
[Abstract](74) [FullText HTML](35)
Isopod crustaceans of the family Dajidae are exclusively marine ectoparasites. The genus Notophryxus G. O. Sars, 1883 currently includes nine nominal species, which are very rarely reported as the chances for encountering these specimens are unpredictable. Our comprehension of the taxonomy, biology, ecology, and life cycle of species belonging to the Notophryxus genus is notably lacking. All nominal species of Notophryxus genus are reviewed here to obtain a comprehensive and integrative taxonomic understanding of this genus, in an attempt to address the lacunae. This paper also documents the rediscovery of an ectoparasitic isopod from the genus Notophryxus in Indian waters, after 55 years. Adult isopod specimens obtained from the outer reefs of Amini Island in the Lakshadweep archipelago, Southeastern Arabian Sea, display morphological congruence to Notophryxus globularis G.O. Sars, 1885. The only previous report on this species dates back to 1885 from G.O. Sars' description of N. globularis as an ectoparasite on the euphausiid Thysanoessa gregaria G.O. Sars, 1883 in the North Pacific. This discovery represents a range extension of N. globularis from the North Pacific to the Arabian Sea. Two cryptoniscid larvae and three adult females of N. globularis (with dwarf males) were found attached to four adult mysid specimens of Siriella aequiremis Hansen, 1910. The present study provides an improved diagnosis of N. globularis with the aid of light microscopy images and line drawings which was not given in the original G O Sars, 1885 report. This research also provides a concise description of cryptoniscid larvae from the same sampling location and same host which is most likely to be N. globularis larvae.
Seasonal influence of freshwater discharge on spatio-temporal variations in primary productivity, sea surface temperature, and euphotic zone depth in the northern Bay of Bengal
Hafez Ahmad, Felix Jose, Md. Simul Bhuyan, Md. Nazrul Islam, Padmanava Dash
 doi: 10.1007/s13131-023-2254-y
[Abstract](63) [FullText HTML](24)
Ocean productivity is the foundation of the marine food web, which continuously removes atmospheric carbon dioxide and supports life at sea and on land. Spatio-temporal variability of net primary productivity (NPP), sea surface temperature (SST), sea surface salinity (SSS), mixed layer depth (MLD), and euphotic zone depth (EZD) in the northern Bay of Bengal (BoB) during the three monsoon seasons were examined in this study based on remote sensing data for the period 2005 to 2020. To compare the NPP distribution between the coastal zones and open BoB, the study area was divided into five zones (Z1-Z5). The results suggest that the most productive Z2 and Z1 are located at the head bay area and are directly influenced by freshwater discharge together with riverine sediment and nutrient loads. Across Z1-Z5, the NPP ranges from 5315.38 mg/(m2·d) to 346.7 mg/(m2·d) (in terms of carbon, since then the same). The highest monthly average NPP of 5315.38 mg/(m2·d) in February and 5039.36 mg/(m2·d) in June were observed from Z2, while the lowest monthly average of 346.72 mg/(m2·d) was observed in March from Z4, which is an oceanic zone. EZD values vary from 6-154 m for the study area, and it has an inverse correlation with NPP concentration. EZD is deeper during the summer season and shallower during the wintertime, with a corresponding increase in productivity. Throughout the year, monthly SST shows slight fluctuation for the entire study area, and statistical analysis showed a significant correlation among NPP, and EZD, overall positive between NPP and MLD, whereas no significant correlation among SSS, and SST for the northern Bay of Bengal. Long-term trends in SST and productivity were significantly positive in head bay zones but negatively productive in the open ocean. The findings in this study on the distribution of NPP, SST, SSS, MLD, and EZD and their seasonal variability in five different zones of BoB can be used to further improve the management of marine resources and overall environmental conditional in response to climate changes in the BoB as they are of utmost relevance to the fisheries for the three bordering countries.
Inter-annual variations of dissolved oxygen and hypoxia off the northern Changjiang River (Yangtze River) Estuary in summer from 1997 to 2014
Anqi Liu, Feng Zhou, Xiao Ma, Qiang Zhao, Guanghong Liao, Yuntao Zhou, Di Tian, Xiaobo Ni, Ruibin Ding
 doi: 10.1007/s13131-023-2244-0
[Abstract](163) [FullText HTML](68)
Hypoxia off the Changjiang River Estuary has been the subject of much attention, yet systematic observations have been lacking, resulting in a lack of knowledge regarding its long-term change and drivers. By revisiting the repeated surveys of dissolved oxygen (DO) and other relevant hydrographic parameters along the section from the Changjiang River Estuary to the Cheju Island in the summer from 1997 to 2014, rather different trends were revealed for the dual low-DO cores. The nearshore low-DO core, located close to the river mouth and relatively stable, shows that hypoxia has become more severe with the lowest DO descending at a rate of −0.07 mg/(L·a) and the thickness of low-DO zone rising at a rate of 0.43 m/a. The offshore core, centered around 40-m isobath but moving back and forth between 123.5°–125°E, shows large fluctuations in the minimum DO concentration, with the thickness of low-DO zone falling at a rate of −1.55 m/a. The probable factors affecting the minimum DO concentration in the two regions also vary. In the nearshore region, the decreasing minimum DO is driven by the increase in both stratification and primary productivity, with the enhanced extension of the Changjiang River Diluted Water (CDW) strengthening stratification. In the offshore region, the fluctuating trend of the minimum DO concentration indicates that both DO loss and DO supplement are distinct. The DO loss is primarily attributed to bottom apparent oxygen utilization caused by the organic matter decay and is also relevant to the advection of low-DO water from the nearshore region. The DO supplement is primarily due to weakened stratification. Our analysis also shows that the minimum DO concentration in the nearshore region was extremely low in 1998, 2003, 2007 and 2010, related to El Niño signal in these summers.
Thermal and exhumation history of the Songnan Low Uplift, Qiongdongnan Basin: constraints from the apatite fission-track and zircon (U-Th)/He thermochronology
Xiaoyin Tang, Kaixun Zhang, Shuchun Yang, Shuai Guo, Xinyan Zhao, Zhizhao Bai
 doi: 10.1007/s13131-023-2253-z
[Abstract](188) [FullText HTML](81)

Significant advancements have been made in the study of Mesozoic granite buried hills in the Songnan Low Uplift (SNLU) of the Qiongdongnan Basin. These findings indicate that the bedrock buried hills in this basin hold great potential for exploration. Borehole samples taken from the granite buried hills in the SNLU were analyzed using apatite fission track (AFT) and zircon (U-Th)/He data to unravel the thermal history of the basement rock. This information is crucial for understanding the processes of exhumation and alteration that occurred after its formation. Thermal modeling of a sample from the western bulge of the SNLU revealed a prolonged cooling event from the late Mesozoic to the Oligocene period (~80−23.8 Ma), followed by a heating stage from the Miocene epoch until the present (~23.8 Ma to present). In contrast, the sample from the eastern bulge experienced a more complex thermal history. It underwent two cooling stages during the late Mesozoic to late Eocene period (~80−36.4 Ma) and the late Oligocene period (~30−23.8 Ma), interspersed with two heating phases during the late Eocene to early Oligocene period (~36.4−30 Ma) and the Miocene epoch to recent times (~23.8−0 Ma), respectively. The differences in exhumation histories between the western and eastern bulges during the late Eocene to Oligocene period in the SNLU can likely be attributed to differences in fault activity. Unlike typical passive continental margin basins, the SNLU has experienced accelerated subsidence after the rifting phase, which began around 5.2 Ma ago. The possible mechanism for this abnormal post-rifting subsidence may be the decay or movement of the deep thermal source and the rapid cooling of the asthenosphere. Long-term and multi-episodic cooling and exhumation processes play a key role in the alteration of bedrock and contribute to the formation of reservoirs. On the other hand, rapid post-rifting subsidence (sedimentation) promotes the formation of cap rocks.

Synthesizing high-resolution satellite salinity data based on multi-fractal fusion
Hengqian Yan, Jian Shi, Ren Zhang, Wangjiang Hu, Yongchui Zhang, Mei Hong
 doi: 10.1007/s13131-023-2209-3
[Abstract](94) [FullText HTML](44)
The spaceborne platform has unprecedently provided the global eddy-permitting (typically ~0.25°) products of Sea Surface Salinity (SSS), however the existing SSS products can hardly resolve mesoscale motions due to the heavy noises therein and the over-smoothing in denoising processes. By means of the Multi-fractal Fusion (MFF), the high-resolution SSS product is synthesized with the template of Sea Surface Temperature (SST). Two low-resolution SSS products and four SST products are considered as the source data and the templates respectively to determine the best combination. The fused products are validated by the in situ observations and intercompared via SSS maps, Singularity Exponent maps and wavenumber spectra. The results demonstrate that the MFF can perform a good work in mitigating the noises and improving the resolution. The Climate Change Initiative (CCI) SSS + the REMote Sensing System (REMSS) SST can produce the 0.1° denoised product whose global mean STandard Derivation (STD) against Argo is 0.21 psu and the feature resolution can reach 30-40 km.
Parameterization, Sensitivity, and Uncertainty of 1-D Thermodynamic Thin-ice Thickness Retrieval
Tianyu Zhang, Mohammed Shokr, Zhida Zhang, Fengming Hui, Xiao Cheng, Zhilun Zhang, Jiechen Zhao, Chunlei Mi
 doi: 10.1007/s13131-023-2210-x
[Abstract](147) [FullText HTML](62)
Retrieval of thin-ice thickness (TIT) using thermodynamic modeling is sensitive to the parameterization of the independent variables (coded in the model) and the uncertainty of the measured input variables. This article examines the deviation of the classical model’s TIT output when using different parameterization schemes and the sensitivity of the output to the ice thickness. Moreover, it estimates the uncertainty of the output in response to the uncertainties of the input variables. The parameterized independent variables include atmospheric longwave emissivity, air density, specific heat of air, latent heat of ice, conductivity of ice, snow depth, and snow conductivity. Measured input parameters include air temperature, ice surface temperature, and wind speed. Among the independent variables, the results show that the highest deviation is caused by adjusting the parameterization of snow conductivity and depth, followed ice conductivity. The sensitivity of the output TIT to ice thickness is highest when using parameterization of ice conductivity, atmospheric emissivity, and snow conductivity and depth. The retrieved TIT obtained using each parameterization scheme is validated using in situ measurements and satellite-retrieved data. From in situ measurements, the uncertainties of the measured air temperature and surface temperature are found to be high. The resulting uncertainties of TIT are evaluated using perturbations of the input data selected based on the probability distribution of the measurement error. The results show that the overall uncertainty of TIT to air temperature, surface temperature, and wind speed uncertainty is around 0.09 m, 0.049 m, and −0.005 m, respectively.
The significant role of submarine groundwater discharge in an Arctic fjord nutrient budget
Xueqing Yu, Jianan Liu, Zhuoyi Zhu, Xiaogang Chen, Tong Peng, Jinzhou Du
 doi: 10.1007/s13131-023-2282-7
[Abstract](96) [FullText HTML](44)
Under global climate change, water flow and related nutrient biogeochemistry in the Arctic are changing at an unprecedented rate, and potentially affect nutrient cycling in the Arctic Ocean. However, nutrient fluxes via submarine groundwater discharge (SGD) are potentially important yet poorly understood in the Arctic. Here we quantified that nutrient fluxes through radium-derived SGD were three orders of magnitude higher than those from the local river and constituted 25-96% of the total nutrient inputs into the Kongsfjorden. These large groundwater nutrient fluxes with high N/P ratio (average 99) may change the biomass and community structure of phytoplankton. Meanwhile, combining other SGD study cases around the Arctic region, SGD rates tend to increase over the past three decades, possibly on account of the effects of global warming. The SGD-derived nutrient may cause the increase of net primary productivity in the Arctic Ocean. The results will provide important basic data for land-ocean interactions in the typical fjord of the Arctic under the influence of global warming.
Responses of the Southern Ocean mixed layer depth to the Eastern and Central Pacific El Niño events during austral winter
Yuxin Shi, Hailong Liu, Xidong Wang, Quanan Zheng
[Abstract](77) [FullText HTML](39)
Based on the Ocean Reanalysis System version 5 (ORAS5) and the fifth-generation reanalysis datasets (ERA5) derived from Medium-Range Weather Forecasts (ECMWF), we investigate the different impacts of the Central Pacific (CP) El Niño and the Eastern Pacific (EP) El Niño on the Southern Ocean (SO) mixed layer depth (MLD) during austral winter. The MLD response to the EP El Niño shows a dipole pattern in the South Pacific, namely the MLD dipole, which is the leading El Niño-induced MLD variability in the SO. The tropical Pacific warm sea surface temperature anomaly (SSTA) signal associated with the EP El Niño excites a Rossby wave train propagating southeastward and then enhances the Amundsen Sea Low (ASL). This results in an anomalous cyclone over the Amundsen Sea. As a result, the anomalous southerly wind to the west of this anomalous cyclone advects colder and drier air into the southeast of New Zealand, leading to surface cooling through less total surface heat flux, especially surface sensible heat (SH) flux and latent heat (LH) flux, and thus contributing to the ML deepening. The east of the anomalous cyclone brings warmer and wetter air to the southwest of Chile, but the total heat flux anomaly shows no significant change. The warm air promotes the sea ice melting and maintains fresh water, which strengthens stratification. This results in a shallower MLD. During the CP El Niño, the response of MLD shows a separate negative MLD anomaly center in the central South Pacific. The Rossby wave train triggered by the warm SSTA in the central Pacific Ocean spreads to the Amundsen Sea, which weakens the ASL. Therefore, the anomalous anticyclone dominates the Amundsen Sea. Consequently, the anomalous northerly wind to the west of anomalous anticyclone advects warmer and wetter air into the central and southern Pacific, causing surface warming through increased SH, LH and longwave (LW) radiation flux, and thus contributing to the ML shoaling. However, to the east of the anomalous anticyclone, there is no statistically significant impact on the MLD.
The impact of typhoons on the biogeochemistry of dissolved organic matter in eutrophic bays in northwestern South China Sea
Xuan Lu, Qibin Lao, Fajin Chen, Guangzhe Jin, Chunqing Chen, Qingmei Zhu
 doi: 10.1007/s13131-023-2283-6
[Abstract](262) [FullText HTML](121)
Highly productive estuaries facilitate intense decomposition of dissolved organic matter (DOM) as a carbon source. However, the specific impacts of typhoons on DOM decomposition in eutrophic bays remain unclear. To address this issue, we investigated the spectral characteristics of DOM before and after Typhoon “Ewiniar” in Zhanjiang Bay, a eutrophic semi-enclosed bay in the northwestern South China Sea. The results revealed that intense microbial decomposition of DOM occurred during the pre-typhoon period because high nutrient inputs facilitated the mobilization of DOM in the bay. However, the intrusion of external seawater induced by the typhoon diluted the nutrient levels in Zhanjiang Bay, reducing the impact of microbial decomposition on DOM during the post-typhoon period. Nevertheless, the net addition of DOM occurred in Zhanjiang Bay during the post-typhoon period, possibly because of the decomposition of particulate organic matter (POM) and desorption of particulate matter. In addition, an increase in apparent oxygen utilization, a decrease in DO saturation and the reduced level of Chl a indicated that organic matter (OM) decomposition was enhanced and OM decomposition shifted to POM decomposition in Zhanjiang Bay after the typhoon. Overall, our study highlighted the shift in the intense OM decomposition from DOM to POM decomposition before and after typhoons in eutrophic bays, providing new insights into the response of typhoons to biogeochemistry.
When river meets ocean: Distribution and conversion of suspended organic particles in a Sundarban mangrove river-estuary system, Bangladesh
Xiaochun Zou, Yunhai Li, Liang Wang, Mohammad Kawser Ahmed, Keliang Chen, Jianwei Wu, Yonghang Xu, Yunpeng Lin, Baohong Chen, Kankan Wu, Jinwen Liu
[Abstract](98) [FullText HTML](48)
Global carbon cycle has received extensive attention, among which the river-estuary system is one of the important links connecting the carbon cycle between land and ocean. In this paper, the distribution and control factors of particulate organic carbon (POC) were studied by using the data of organic carbon contents and its carbon isotopic composition (δ13C) in the mainstream and estuary of Passur River in the Sundarban area, combined with the hydrological and biological data measured by CTD. The results show that POC content ranged from 0.263 to 9.292 mg/L, and the POC content in the river section (averaged 4.129 mg/L) was significantly higher than that in the estuary area (averaged 0.858 mg/L). Two distinct stages of POC transport from land to sea in the Sundarban area were identified. The first stage occurred in the river section, where POC distribution was mainly controlled by the dynamic process of runoff and the organic carbon was mainly terrestrial source. The second stage occurred during estuarine mixing, where the POC distribution was mainly controlled by the mixing process of seawater and freshwater. The source of POC was predominantly marine and exhibiting vertical differences. The surface and middle layers were primarily influenced by marine sources, while the bottom layer was jointly controlled by terrestrial and marine sources of organic carbon. These findings are of great significance for understanding the carbon cycle in such a large mangrove ecosystem like the Sundarban Mangrove.
Prediction of three-dimensional ocean temperature in the South China Sea based on time series gridded data and a dynamic spatiotemporal graph neural network
Feng Nan, Zhuolin Li, Jie Yu, Suixiang Shi, Xinrong Wu, Lingyu Xu
[Abstract](109) [FullText HTML](53)
Ocean temperature is an important physical variable in marine ecosystems, and ocean temperature prediction is an important research objective in ocean-related fields. Currently, one of the commonly used methods for ocean temperature prediction is based on data-driven, but research on this method is mostly limited to the sea surface, with few studies on the prediction of internal ocean temperature. Existing graph neural network-based methods usually use predefined graphs or learned static graphs, which cannot capture the dynamic associations among data. In this study, we propose a novel dynamic spatiotemporal graph neural network (DSTGN) to predict three-dimensional ocean temperature (3D-OT), which combines static graph learning and dynamic graph learning to automatically mine two unknown dependencies between sequences based on the original 3D-OT data without prior knowledge. Temporal and spatial dependencies in the time series were then captured using temporal and graph convolutions. We also integrated dynamic graph learning, static graph learning, graph convolution, and temporal convolution into an end-to-end framework for 3D-OT prediction using time-series grid data. In this study, we conducted prediction experiments using high-resolution 3D-OT from the Copernicus global ocean physical reanalysis, with data covering the vertical variation of temperature from the sea surface to 1,000 m below the sea surface. We compared five mainstream models that are commonly used for ocean temperature prediction, and the results showed that the method achieved the best prediction results at all prediction scales.
Bioturbation coefficients and organic carbon degradation rates of deep-sea sediments in the central-eastern tropical Pacific
Feng Lin, Cai Lin, Xiuwu Sun, Hui Lin, Li Lin, Fangfang Deng, Kaiwen Tan, Peng Lin
[Abstract](83) [FullText HTML](40)
The biogeochemical processes of marine sediments are influenced by bioturbation and organic carbon decomposition, which is crucial for understanding global element cycles and climate change. Two sediment cores were acquired in 2017 from abyssal basins in the central-eastern tropical Pacific to determine the bioturbation and organic carbon degradation processes. The radioactivity concentrations of 210Pb and 226Ra in the sediment cores were measured, indicating the presence of significant excess 210Pb (210Pbex) signals in the sediment cores. Besides, a manganese nodule was discovered in one core, which had a substantial influence on the distribution of 210Pbex. With the exception of this anomalous finding, the bioturbation coefficients in the remaining core were estimated to be 10.6 cm2/a using a steady-state diffusion model, greater than most of the deep-sea sediments from the Equatorial Eastern Pacific. By using a bio-diffusion model, we further calculated the degradation rates of organic carbon (8.02 ka-1), which is also higher than other areas of the Pacific. Our findings displayed the presence of a biologically active benthic ecosystem in the central-eastern tropical Pacific.
Evaluation and projection of marine heatwaves in the South China Sea: insights from CMIP6 multi-model ensemble
Kai Liu, Kang Xu, Tongxin Han, Congwen Zhu, Nina Li, Anboyu Guo, Xiaolu Huang
[Abstract](88) [FullText HTML](45)
This study evaluates the performance of 16 models sourced from the Coupled Model Intercomparison Project phase 6 (CMIP6) in simulating marine heatwaves (MHWs) in the South China Sea (SCS) during the historical period (1982−2014), and also investigates future changes in SCS MHWs based on simulations from three Shared Socioeconomic Pathway (SSP) scenarios (SSP126, SSP245, and SSP585) using CMIP6 models. Results demonstrate that the CMIP6 models perform well in simulating the spatial-temporal distribution and intensity of SCS MHWs, with their multi-model ensemble (MME) results showing the best performance. The reasonable agreement between the observations and CMIP6 MME reveals that the increasing trends of SCS MHWs are attributed to the warming sea surface temperature trend. Under various SSP scenarios, the year 2040 emerges as pivotal juncture for future shifts in SCS MHWs, marked by distinct variations in changing rate and amplitudes. This is characterized by an accelerated decrease in MHWs frequency and a notably heightened increase in mean intensity, duration, and total days after 2040. Furthermore, the projection results for SCS MHWs suggest that the spatial pattern of MHWs remains consistent across future periods. However, the intensity shows higher consistency only during the near-term period (2021−2050), while notable inconsistencies are observed during the medium-term (2041−2700) and long-term (2701−2100) periods under the three SSP scenarios. During the near-term period, the SCS MHWs are characterized by moderate and strong events with high frequencies and relatively shorter durations. In contrast, during the medium-term period, MHWs are also characterized by moderate and strong events, but with longer-lasting and more intense events under the SSP245 and SSP585 scenarios. However, in the long-term period, extreme MHWs become the dominant feature under the SSP585 scenario, indicating a substantial intensification of SCS MHWs, effectively establishing a near-permanent state.
Tetrabromobisphenol A and hexabromocyclododecane in sediments from the Pearl River Estuary and South China Sea
Chuyue Long, Weiyan Yang, Jiaxun Lu, Yuanyue Cheng, Ning Qiu, Sen Du, Li Zhang, Shejun Chen, Yuxin Sun
 doi: 10.1007/s13131-023-2267-6
[Abstract](150) [FullText HTML](61)
Marine sediments were collected from the Pearl River Estuary (PRE) and South China Sea (SCS) to study the occurrence and spatial distribution of tetrabromobisphenol A (TBBPA) and hexabromocyclododecane (HBCDD). The levels of TBBPA and HBCDD in sediments ranged from not detected (nd) to 6.14 ng/g dry weight (dw) and nd to 0.42 ng/g dw. TBBPA concentrations in marine sediments were substantially higher than HBCDD. The concentrations of TBBPA and HBCDD in the PRE sediments were significantly greater than those in the SCS. α-HBCDD (48.7%) and γ-HBCDD (46.2%) were the two main diastereoisomers of HBCDD in sediments from the PRE, with minor contribution of β-HBCDD (5.1%). HBCDD were only found in one sample from the northern SCS. The enantiomeric fraction of α-HBCDD in sediments from the PRE was obviously greater than 0.5, indicating an accumulation of (+)-α-HBCDD. The enantiomers of HBCDD were not measured in sediments from the SCS. This work highlighted the environmental behaviors of TBBPA and HBCDD in marine sediments.
Erratum to: Acta Oceanologica Sinica (2022) 41(10): 119–130DOI: 10.1007/s13131-022-2023-3The atmospheric hinder for intraseasonal sea-air interaction over the Bay of Bengal during Indian summer monsoon in CMIP6
Ze Meng, Lei Zhou, Baosheng Li, Jianhuang Qin, Juncheng Xie
 doi: 10.1007/s13131-022-2131-0
[Abstract](232) [FullText HTML](80)
Forecasting the western Pacific subtropical high index during typhoon activity using a hybrid deep learning model
Jianyin Zhou, Jie Xiang, Huadong Du, Suhong Ma
[Abstract](349) [FullText HTML](133)
Seasonal location and intensity changes in the western Pacific subtropical high (WPSH) are important factors dominating the synoptic weather and the distribution and magnitude of precipitation in the rain belt over East Asia. Therefore, this article delves into the forecast of the western Pacific subtropical high index during typhoon activity by adopting a hybrid deep learning model. Firstly, the predictors, which are the inputs of the model, are analysed based on three characteristics: the first is the statistical discipline of the WPSH index anomalies corresponding to the three types of typhoon paths; the second is the correspondence of distributions between sea surface temperature (SST), 850 hPa zonal wind (u), meridional wind (v), and 500 hPa potential height field; and the third is the numerical sensitivity experiment, which reflects the evident impact of variations in the physical field around the typhoon to the WPSH index. Secondly, the model is repeatedly trained through the backward propagation algorithm to predict the WPSH index using 2011-2018 atmospheric variables as the input of the training set. The model predicts the WPSH index after 6 h, 24 h, 48 h, and 72 h. The validation set using independent data in 2019 is utilized to illustrate the performance. Finally, the model is improved by changing the CNN2D module to the DeCNN module to enhance its ability to predict images. Taking the 2019 Typhoon Lekima as an example, it shows the promising performance of this model to predict the 500 hPa potential height field.
Diversity of protease-producing bacteria in the Bohai Bay sediment and their extracellular enzymatic properties
Zhenpeng Zhang, Chaoya Wu, Shuai Shao, Wei Liu, En-Tao Wang, Yan Li
 doi: 10.1007/s13131-020-1589-x
[Abstract](676) [FullText HTML](204)
Protease-producing bacteria play key roles in the degradation of organic nitrogen materials in marine sediments. However, their diversity, production of proteases and other extracellular enzymes, even in situ ecological functions remain largely unknown. In this study, we investigated the diversity of cultivable extracellular protease-producing bacteria in the sediments of the Bohai Bay. A total of 109 bacterial isolates were obtained from the sediments of 7 stations. The abundance of cultivable protease-producing bacteria was about 104 CFU/g of sediment in all the samples. Phylogenetic analysis based on 16S rRNA gene sequences classified all the isolates into 14 genera from phyla Proteobacteria, Firmicutes, Bacteroidetes and Actinobacteria, with Pseudoalteromonas (63/109, 57.8%), Bacillus (9/109, 8.2%), Sulfitobacter (8/109, 7.3%) and Salegentibacter (6/109, 5.5%) as the dominant taxa. Enzymatic inhibition tests indicated that all the tested isolates produced serine and/or metalloprotease, with only a small proportion producing cysteine and/or aspartic proteases. Several extracellular enzyme activities, including alginase, lipase, amylase and cellulose, and nitrate reduction were also detected for strains with higher protease activities. According the results, the protease-producing bacteria could also be participate in many biogeochemical processes in marine sediments. Our study broadened understanding and knowledge on the potential ecological functions of protease-producing bacteria in marine sediments.
2024-3 Cover
2024, 43(3).  
[Abstract](63) [FullText HTML](33) [PDF 7033KB](7)
2024-3 Contents
2024, 43(3).  
[Abstract](56) [FullText HTML](27) [PDF 65KB](2)
Articles$Physical Oceanography, Marine Meteorology and Marine Physics
Study on the interannual variability of the Kerama Gap transport and its relation to the Kuroshio/Ryukyu Current system
Han Zhou, Kai Yu, Jianhuang Qin, Xuhua Cheng, Meixiang Chen, Changming Dong
2024, 43(3): 1-14.   doi: 10.1007/s13131-023-2281-8
[Abstract](317) [FullText HTML](153) [PDF 6312KB](29)
An analysis of a 68-year monthly hindcast output from an eddy-resolving ocean general circulation model reveals the relationship between the interannual variability of the Kerama Gap transport (KGT) and the Kuroshio/Ryukyu Current system. The study found a significant difference in the interannual variability of the upstream and downstream transports of the East China Sea- (ECS-) Kuroshio and the Ryukyu Current. The interannual variability of the KGT was found to be of paramount importance in causing the differences between the upstream and downstream ECS-Kuroshio. Additionally, it contributed approximately 37% to the variability of the Ryukyu Current. The interannual variability of the KGT was well described by a two-layer rotating hydraulic theory. It was dominated by its subsurface-intensified flow core, and the upper layer transport made a weaker negative contribution to the total KGT. The subsurface flow core was found to be mainly driven by the subsurface pressure head across the Kerama Gap, and the pressure head was further dominated by the subsurface density anomalies on the Pacific side. These density anomalies could be traced back to the eastern open ocean, and their propagation speed was estimated to be about 7.4 km/d, which is consistent with the speed of the local first-order baroclinic Rossby wave. When the negative (positive) density anomaly signal reached the southern region of the Kerama Gap, it triggered the increase (decrease) of the KGT towards the Pacific side and the formation of an anticyclonic (cyclonic) vortex by baroclinic adjustment. Meanwhile, there is an increase (decrease) in the upstream transport of the entire Kuroshio/Ryukyu Current system and an offshore flow that decreases (increases) the downstream Ryukyu Current.
Observing eddy dye patches induced by shear instabilities in the surf zone on a plane beach
Chunping Ren, Nannan Fu, Chong Yu, Yuchuan Bai, Kezhao Fang
2024, 43(3): 15-29.   doi: 10.1007/s13131-023-2270-y
[Abstract](109) [FullText HTML](41) [PDF 4424KB](16)
The effects of surf zone eddy generated by alongshore currents on the deformation and transport of dye are still poorly understood, and related tracer release experiments are lacking. Therefore, a tracer release laboratory experiment was conducted under monochromatic, unidirectional incident waves with a large incident angle (30°) on a plane beach with a 1:100 slope in a large wave basin. A charge-coupled device suspended above the basin recorded the dye patch image. The evolution of eddy dye patch was observed and the transport and diffusion were analyzed based on the collected images. Subsequently, a linear instability numerical model was adopted to calculate the perturbation velocity field at the initial stage. The observation and image processing results show that surf zone eddy patches occurred and were separated from the original dye patches. Our numerical analysis results demonstrate that the structure of the perturbation velocity field is consistent with the experimental observations, and that the ejection of eddy patches shoreward or offshore may be ascribed to the double vortex.
Application of the finite analytic numerical method to a flow-dependent variational data assimilation
Yan Hu, Wei Li, Xuefeng Zhang, Guimei Liu, Liang Zhang
2024, 43(3): 30-39.   doi: 10.1007/s13131-023-2229-z
[Abstract](48) [FullText HTML](22) [PDF 3483KB](1)
An anisotropic diffusion filter can be used to model a flow-dependent background error covariance matrix, which can be achieved by solving the advection-diffusion equation. Because of the directionality of the advection term, the discrete method needs to be chosen very carefully. The finite analytic method is an alternative scheme to solve the advection-diffusion equation. As a combination of analytical and numerical methods, it not only has high calculation accuracy but also holds the characteristic of the auto upwind. To demonstrate its ability, the one-dimensional steady and unsteady advection-diffusion equation numerical examples are respectively solved by the finite analytic method. The more widely used upwind difference method is used as a control approach. The result indicates that the finite analytic method has higher accuracy than the upwind difference method. For the two-dimensional case, the finite analytic method still has a better performance. In the three-dimensional variational assimilation experiment, the finite analytic method can effectively improve analysis field accuracy, and its effect is significantly better than the upwind difference and the central difference method. Moreover, it is still a more effective solution method in the strong flow region where the advective-diffusion filter performs most prominently.
A typhoon-induced storm surge numerical model with GPU acceleration based on an unstructured spherical centroidal Voronoi tessellation grid
Yuanyong Gao, Fujiang Yu, Cifu Fu, Jianxi Dong, Qiuxing Liu
2024, 43(3): 40-47.   doi: 10.1007/s13131-023-2175-9
[Abstract](215) [FullText HTML](88) [PDF 1827KB](16)
Storm surge is often the marine disaster that poses the greatest threat to life and property in coastal areas. Accurate and timely issuance of storm surge warnings to take appropriate countermeasures is an important means to reduce storm surge-related losses. Storm surge numerical models are important for storm surge forecasting. To further improve the performance of the storm surge forecast models, we developed a numerical storm surge forecast model based on an unstructured spherical centroidal Voronoi tessellation (SCVT) grid. The model is based on shallow water equations in vector-invariant form, and is discretized by Arakawa C grid. The SCVT grid can not only better describe the coastline information but also avoid rigid transitions, and it has a better global consistency by generating high-resolution grids in the key areas through transition refinement. In addition, the simulation speed of the model is accelerated by using the openACC-based GPU acceleration technology to meet the timeliness requirements of operational ensemble forecast. It only takes 37 s to simulate a day in the coastal waters of China. The newly developed storm surge model was applied to simulate typhoon-induced storm surges in the coastal waters of China. The hindcast experiments on the selected representative typhoon-induced storm surge processes indicate that the model can reasonably simulate the distribution characteristics of storm surges. The simulated maximum storm surges and their occurrence times are consistent with the observed data at the representative tide gauge stations, and the mean absolute errors are 3.5 cm and 0.6 h respectively, showing high accuracy and application prospects.
Influence of the Atlantic Multidecadal Oscillation and Interdecadal Pacific Oscillation on Antarctic surface air temperature during 1900 to 2015
Cuijuan Sui, Lejiang Yu, Alexey Yu. Karpechko, Licheng Feng, Shan Liu
2024, 43(3): 48-58.   doi: 10.1007/s13131-023-2247-x
[Abstract](112) [FullText HTML](50) [PDF 14932KB](5)
The importance of the Atlantic Multidecadal Oscillation (AMO) and Interdecadal Pacific Oscillation (IPO) in influencing zonally asymmetric changes in Antarctic surface air temperature (SAT) has been established. However, previous studies have primarily concentrated on examining the combined impact of the contrasting phases of the AMO and IPO, which have been dominant since the advent of satellite observations in 1979. This study utilizes long-term reanalysis data to investigate the impact of four combinations of +AMO+IPO, –AMO–IPO, +AMO–IPO, and –AMO+IPO on Antarctic SAT over the past 115 years. The +AMO phase is characterized by a spatial mean temperature amplitude of up to 0.5℃ over the North Atlantic Ocean, accompanied by positive sea surface temperature (SST) anomalies in the tropical eastern Pacific and negative SST anomalies in the extratropical-mid-latitude western Pacific, which are indicative of the +IPO phase. The Antarctic SAT exhibits contrasting spatial patterns during the +AMO+IPO and +AMO–IPO periods. However, during the –AMO+IPO period, apart from the Antarctic Peninsula and the vicinity of the Weddell Sea, the entire Antarctic region experiences a warming trend. The most pronounced signal in the SAT anomalies is observed during the austral autumn, whereas the combination of –AMO and –IPO exhibits the smallest magnitude across all the combinations. The wavetrain excited by the SST anomalies associated with the AMO and IPO induces upper-level and surface atmospheric circulation anomalies, which alter the SAT anomalies. Furthermore, downward longwave radiation anomalies related to anomalous cloud cover play a crucial role. In the future, if the phases of AMO and IPO were to reverse (AMO transitioning to a negative phase and IPO transitioning to a positive phase), Antarctica could potentially face more pronounced warming and accelerated melting compared to the current observations.
Characteristics and triggering mechanisms of early negative Indian Ocean Dipole
Yue Fang, Shuangwen Sun, Yongcan Zu, Jianhu Wang, Lin Feng
2024, 43(3): 59-65.   doi: 10.1007/s13131-023-2294-y
[Abstract](136) [FullText HTML](60) [PDF 1418KB](15)
Negative Indian Ocean Dipole (nIOD) can exert great impacts on global climate and can also strongly influence the climate in China. Early nIOD is a major type of nIOD, which can induce more pronounced climate anomalies in summer than La Niña-related nIOD. However, the characteristics and triggering mechanisms of early nIOD are unclear. Our results based on reanalysis datasets indicate that the early nIOD and La Niña-related nIOD are the two major types of nIOD, and the former accounts for over one third of all the nIOD events in the past six decades. These two types of nIODs are similar in their intensities, but are different in their spatial patterns and seasonal cycles. The early nIOD, which develops in spring and peaks in summer, is one season earlier than the La Niña-related nIOD. The spatial pattern of the wind anomaly associated with early nIOD exhibits a winter monsoon-like pattern, with strong westerly anomalies in the equatorial Indian Ocean and eastly anomalies in the northern Indian Ocean. Opposite to the triggering mechanism of early positve IOD, the early nIOD is induced by delayed Indian summer monsoon onset. The results of this study are helpful for improving the prediction skill of IOD and its climate impacts.
The environmental analysis and site selection of mussel and large yellow croaker aquaculture areas based on high resolution remote sensing
Lina Cai, Jie Yin, Xiaojun Yan, Yongdong Zhou, Rong Tang, Menghan Yu
2024, 43(3): 66-86.   doi: 10.1007/s13131-023-2284-5
[Abstract](135) [FullText HTML](62) [PDF 8755KB](19)
Mussel aquaculture and large yellow croaker aquaculture areas and their environmental characteristics in Zhoushan were analyzed using satellite data and in-situ surveys. A new two-step remote sensing method was proposed and applied to determine the basic environmental characteristics of the best mussel and large yellow croaker aquaculture areas. This methodology includes the first step of extraction of the location distribution and the second step of the extraction of internal environmental factors. The fishery ranching index (FRI1, FRI2) was established to extract the mussel and the large yellow croaker aquaculture area in Zhoushan, using Gaofen-1 (GF-1) and Gaofen-6 (GF-6) satellite data with a special resolution of 2 m. In the second step, the environmental factors such as sea surface temperature (SST), chlorophyll a (Chl-a) concentration, current and tide, suspended sediment concentration (SSC) in mussel aquaculture area and large yellow croaker aquaculture area were extracted and analyzed in detail. The results show the following three points. (1) For the extraction of the mussel aquaculture area, FRI1 and FRI2 are complementary, and the combination of FRI1 and FRI2 is suitable to extract the mussel aquaculture area. As for the large yellow croaker aquaculture area extraction, FRI2 is suitable. (2) Mussel aquaculture and the large yellow croaker aquaculture area in Zhoushan are mainly located on the side near the islands that are away from the eastern open waters. The water environment factor template suitable for mussel and large yellow croaker aquaculture was determined. (3) This two-step remote sensing method can be used for the preliminary screening of potential site selection for the mussels and large yellow croaker aquaculture area in the future. the fishery ranching index (FRI1, FRI2) in this paper can be applied to extract the mussel and large yellow croaker aquaculture areas in coastal waters around the world.
Articles$Marine Information Science
Retrieval of Antarctic sea ice freeboard and thickness from HY-2B satellite altimeter data
Yizhuo Chen, Xiaoping Pang, Qing Ji, Zhongnan Yan, Zeyu Liang, Chenlei Zhang
2024, 43(3): 87-101.   doi: 10.1007/s13131-023-2250-2
[Abstract](64) [FullText HTML](34) [PDF 3907KB](2)
Antarctic sea ice is an important part of the Earth’s atmospheric system, and satellite remote sensing is an important technology for observing Antarctic sea ice. Whether Chinese Haiyang-2B (HY-2B) satellite altimeter data could be used to estimate sea ice freeboard and provide alternative Antarctic sea ice thickness information with a high precision and long time series, as other radar altimetry satellites can, needs further investigation. This paper proposed an algorithm to discriminate leads and then retrieve sea ice freeboard and thickness from HY-2B radar altimeter data. We first collected the Moderate-resolution Imaging Spectroradiometer ice surface temperature (IST) product from the National Aeronautics and Space Administration to extract leads from the Antarctic waters and verified their accuracy through Sentinel-1 Synthetic Aperture Radar images. Second, a surface classification decision tree was generated for HY-2B satellite altimeter measurements of the Antarctic waters to extract leads and calculate local sea surface heights. We then estimated the Antarctic sea ice freeboard and thickness based on local sea surface heights and the static equilibrium equation. Finally, the retrieved HY-2B Antarctic sea ice thickness was compared with the CryoSat-2 sea ice thickness and the Antarctic Sea Ice Processes and Climate (ASPeCt) ship-based observed sea ice thickness. The results indicate that our classification decision tree constructed for HY-2B satellite altimeter measurements was reasonable, and the root mean square error of the obtained sea ice thickness compared to the ship measurements was 0.62 m. The proposed sea ice thickness algorithm for the HY-2B radar satellite fills a gap in this application domain for the HY-series satellites and can be a complement to existing Antarctic sea ice thickness products; this algorithm could provide long-time-series and large-scale sea ice thickness data that contribute to research on global climate change.
Spatiotemporal variation and freeze-thaw asymmetry of Arctic sea ice in multiple dimensions during 1979 to 2020
Yu Guo, Xiaoli Wang, He Xu, Xiyong Hou
2024, 43(3): 102-114.   doi: 10.1007/s13131-023-2296-9
[Abstract](140) [FullText HTML](67) [PDF 6838KB](7)
Arctic sea ice is broadly regarded as an indicator and amplifier of global climate change. The rapid changes in Arctic sea ice have been widely concerned. However, the spatiotemporal changes in the horizontal and vertical dimensions of Arctic sea ice and its asymmetry during the melt and freeze seasons are rarely quantified simultaneously based on multiple sources of the same long time series. In this study, the spatiotemporal variation and freeze-thaw asymmetry of Arctic sea ice were investigated from both the horizontal and vertical dimensions during 1979–2020 based on remote sensing and assimilation data. The results indicated that Arctic sea ice was declining at a remarkably high rate of –5.4 × 104 km2/a in sea ice area (SIA) and –2.2 cm/a in sea ice thickness (SIT) during 1979 to 2020, and the reduction of SIA and SIT was the largest in summer and the smallest in winter. Spatially, compared with other sub-regions, SIA showed a sharper declining trend in the Barents Sea, Kara Sea, and East Siberian Sea, while SIT presented a larger downward trend in the northern Canadian Archipelago, northern Greenland, and the East Siberian Sea. Regarding to the seasonal trend of sea ice on sub-region scale, the reduction rate of SIA exhibited an apparent spatial heterogeneity among seasons, especially in summer and winter, i.e., the sub-regions linked to the open ocean exhibited a higher decline rate in winter; however, the other sub-regions blocked by the coastlines presented a greater decline rate in summer. For SIT, the sub-regions such as the Beaufort Sea, East Siberian Sea, Chukchi Sea, Central Arctic, and Canadian Archipelago always showed a higher downward rate in all seasons. Furthermore, a striking freeze-thaw asymmetry of Arctic sea ice was also detected. Comparing sea ice changes in different dimensions, sea ice over most regions in the Arctic showed an early retreat and rapid advance in the horizontal dimension but late melting and gradual freezing in the vertical dimension. The amount of sea ice melting and freezing was disequilibrium in the Arctic during the considered period, and the rate of sea ice melting was 0.3 × 104 km2/a and 0.01 cm/a higher than that of freezing in the horizontal and vertical dimensions, respectively. Moreover, there were notable shifts in the melting and freezing of Arctic sea ice in 1997/2003 and 2000/2004, respectively, in the horizontal/vertical dimension.
A multi-scale second-order autoregressive recursive filter approach for the sea ice concentration analysis
Lu Yang, Xuefeng Zhang
2024, 43(3): 115-126.   doi: 10.1007/s13131-023-2297-8
[Abstract](88) [FullText HTML](32) [PDF 3237KB](6)
To effectively extract multi-scale information from observation data and improve computational efficiency, a multi-scale second-order autoregressive recursive filter (MSRF) method is designed. The second-order autoregressive filter used in this study has been attempted to replace the traditional first-order recursive filter used in spatial multi-scale recursive filter (SMRF) method. The experimental results indicate that the MSRF scheme successfully extracts various scale information resolved by observations. Moreover, compared with the SMRF scheme, the MSRF scheme improves computational accuracy and efficiency to some extent. The MSRF scheme can not only propagate to a longer distance without the attenuation of innovation, but also reduce the mean absolute deviation between the reconstructed sea ice concentration results and observations reduced by about 3.2 % compared to the SMRF scheme. On the other hand, compared with traditional first-order recursive filters using in the SMRF scheme that multiple filters are executed, the MSRF scheme only needs to perform two filter processes in one iteration, greatly improving filtering efficiency. In the two-dimensional experiment of sea ice concentration, the calculation time of the MSRF scheme is only 1/7 of that of SMRF scheme. This means that the MSRF scheme can achieve better performance with less computational cost, which is of great significance for further application in real-time ocean or sea ice data assimilation systems in the future.
An improved algorithm for retrieving thin sea ice thickness in the Arctic Ocean from SMOS and SMAP L-band radiometer data
Lian He, Senwen Huang, Fengming Hui, Xiao Cheng
2024, 43(3): 127-138.   doi: 10.1007/s13131-023-2280-9
[Abstract](118) [FullText HTML](57) [PDF 3246KB](2)
The aim of this study was to develop an improved thin sea ice thickness (SIT) retrieval algorithm in the Arctic Ocean from the Soil Moisture Ocean Salinity and Soil Moisture Active Passive L-band radiometer data. This SIT retrieval algorithm was trained using the simulated SIT from the cumulative freezing degree days model during the freeze-up period over five carefully selected regions in the Beaufort, Chukchi, East Siberian, Laptev and Kara seas and utilized the microwave polarization ratio (PR) at incidence angle of 40°. The improvements of the proposed retrieval algorithm include the correction for the sea ice concentration impact, reliable reference SIT data over different representative regions of the Arctic Ocean and the utilization of microwave polarization ratio that is independent of ice temperature. The relationship between the SIT and PR was found to be almost stable across the five selected regions. The SIT retrievals were then compared to other two existing algorithms (i.e., UH_SIT from the University of Hamburg and UB_SIT from the University of Bremen) and validated against independent SIT data obtained from moored upward looking sonars (ULS) and airborne electromagnetic (EM) induction sensors. The results suggest that the proposed algorithm could achieve comparable accuracies to UH_SIT and UB_SIT with root mean square error (RMSE) being about 0.20 m when validating using ULS SIT data and outperformed the UH_SIT and UB_SIT with RMSE being about 0.21 m when validatng using EM SIT data. The proposed algorithm can be used for thin sea ice thickness (<1.0 m) estimation in the Arctic Ocean and requires less auxiliary data in the SIT retrieval procedure which makes its implementation more practical.
Hyperspectral remote sensing identification of marine oil emulsions based on the fusion of spatial and spectral features
Xinyue Huang, Yi Ma, Zongchen Jiang, Junfang Yang
2024, 43(3): 139-154.   doi: 10.1007/s13131-023-2249-8
[Abstract](151) [FullText HTML](66) [PDF 11530KB](10)
Marine oil spill emulsions are difficult to recover, and the damage to the environment is not easy to eliminate. The use of remote sensing to accurately identify oil spill emulsions is highly important for the protection of marine environments. However, the spectrum of oil emulsions changes due to different water content. Hyperspectral remote sensing and deep learning can use spectral and spatial information to identify different types of oil emulsions. Nonetheless, hyperspectral data can also cause information redundancy, reducing classification accuracy and efficiency, and even overfitting in machine learning models. To address these problems, an oil emulsion deep-learning identification model with spatial-spectral feature fusion is established, and feature bands that can distinguish between crude oil, seawater, water-in-oil emulsion (WO), and oil-in-water emulsion (OW) are filtered based on a standard deviation threshold–mutual information method. Using oil spill airborne hyperspectral data, we conducted identification experiments on oil emulsions in different background waters and under different spatial and temporal conditions, analyzed the transferability of the model, and explored the effects of feature band selection and spectral resolution on the identification of oil emulsions. The results show the following. (1) The standard deviation–mutual information feature selection method is able to effectively extract feature bands that can distinguish between WO, OW, oil slick, and seawater. The number of bands was reduced from 224 to 134 after feature selection on the Airborne Visible Infrared Imaging Spectrometer (AVIRIS) data and from 126 to 100 on the S185 data. (2) With feature selection, the overall accuracy and Kappa of the identification results for the training area are 91.80% and 0.86, respectively, improved by 2.62% and 0.04, and the overall accuracy and Kappa of the identification results for the migration area are 86.53% and 0.80, respectively, improved by 3.45% and 0.05. (3) The oil emulsion identification model has a certain degree of transferability and can effectively identify oil spill emulsions for AVIRIS data at different times and locations, with an overall accuracy of more than 80%, Kappa coefficient of more than 0.7, and F1 score of 0.75 or more for each category. (4) As the spectral resolution decreasing, the model yields different degrees of misclassification for areas with a mixed distribution of oil slick and seawater or mixed distribution of WO and OW. Based on the above experimental results, we demonstrate that the oil emulsion identification model with spatial–spectral feature fusion achieves a high accuracy rate in identifying oil emulsion using airborne hyperspectral data, and can be applied to images under different spatial and temporal conditions. Furthermore, we also elucidate the impact of factors such as spectral resolution and background water bodies on the identification process. These findings provide new reference for future endeavors in automated marine oil spill detection.

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