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Contributions of annual and semiannual tidal constituents to chart datum in the adjacent seas of China
Yikai Feng, Yanguang Fu, Long Yang, Dongxu Zhou
 doi: 10.1007/s13131-023-2231-5
[Abstract](82) [FullText HTML](39)
Global uniform chart datum (CD) surface construction is the basic upon which to realize various vertical datums transformation, and is of great importance for geospatial data expression under the same vertical datum. Generally, the CD level is computed by developing the function between tidal constituents’ harmonic constants and time, i.e., the lowest astronomical tide is taken as the lowest predicted tide level by adopting the major constituents over a 19-a period. The CD surface prescribed in China is the theoretical lowest tide (TLT) and is calculated using 13 tidal constituents, i.e., short -period (Q1, O1, P1, K1, N2, M2, S2, K2, M4, MS4 and M6) and long-period (Sa and Ssa) tidal constituents. Although the accuracy in determining short-period tidal constituents has improved gradually, the long-period tide has not been studied thoroughly owing to nonstationary and temporal variations. Previous studies have intended to evaluate the effect of Sa and Ssa tides in the determination of the TLT level for the purpose of determining a more accurate CD surface for the adjacent seas of China. Here, the parameters of long-period tidal correction and long-period tidal correction rate were treated as the effect of both Sa and Ssa on the TLT, and the TOPEX/Poseidon and Jason series satellite altimetry data ranged from October 1992 to April 2022 were adopted to analyze the contribution of long-period tidal constituents. Results showed that the average long-period correction value is 10.10 cm (range from 8.57 cm to 14.98 cm), and that the average long-period tidal contribution rate is 14.56% (range from 9.09% to 23.97%) in the adjacent seas of China. Finally, data from 82 tide gauge station with at least a 1-a record of hourly observations were compared with satellite-derived result. We concluded that the long-period tidal contribution should not be neglected in TLT construction. Furthermore, to reduce tidal datum uncertainty, accurate extraction of long-period tidal constituents should receive closer attentions.
What induced the trend shift of mixed-layer depths in the Antarctic Circumpolar Current region in the mid-1980s?
Shan Liu, Jingzhi Su, Huijun Wang, Cuijuan Sui
 doi: 10.1007/s13131-023-2268-5
[Abstract](14) [FullText HTML](7)
An obvious trend shift in the annual mean and winter mixed layer depth (MLD) in the Antarctic Circumpolar Current (ACC) region was detected during the 1960–2021 period. Shallowing trends stopped in mid-1980s, followed by a period of weak trends. The MLD deepening trend difference between the two period were mainly distributed in the western areas in the Drake Passage, the areas north to Victoria Land and Wilkes Land, and the central parts of the South Indian sector. The newly formed ocean current shear due to the meridional shift of the ACC flow axis between the two periods is the dominant driver for the MLD trends shift distributed in the western areas in the Drake Passage and the central parts of the South Indian sector. The saltier trends in the regions north to Victoria Land and Wilkes Land could be responsible for the strengthening mixing processes in this region.
A positive trend in the stability of global offshore wind energy
Chongwei Zheng
 doi: 10.1007/s13131-023-2187-5
[Abstract](2) [FullText HTML](1)
The recognition on the trend of wind energy stability is still extremely rare, although it is closely related to acquisition efficiency, grid connection, equipment lifetime, and costs of wind energy utilization. Using the 40-year (1979–2018) ERA-Interim data from the European Center for Medium-Range Weather Forecasts (ECMWF), this study presented the spatial-temporal distribution and climatic trend of the stability of global offshore wind energy as well as the abrupt phenomenon of wind energy stability in key regions over the past 40 years with the climatic analysis method and Mann-Kendall (M-K) test. The results show the following 5 points. (1) According to the coefficient of variation (Cv) of the wind power density (WPD), there are six permanent stable zones of global offshore wind energy: the southeast and northeast trade wind zones in the Indian, Pacific and Atlantic Oceans, the Southern Hemisphere westerly, and a semi-permanent stable zone (North Indian Ocean). (2) There are six low-value zones for both seasonal variability index (Sv) and monthly variability index (Mv) globally, with a similar spatial distribution as that of the six permanent stable zones. The Mv and Sv in the Arabian Sea are the highest in the world. (3) After the Cv, Mv and Sv are comprehensively considered, the six permanent stable zones have an obvious advantage in the stability of wind energy over other sea areas, with Cv below 0.8, Mv within 1.0, and Sv within 0.7 all the year round. (4) The global stability of offshore wind energy shows a positive climatic trend for the past four decades. The Cv, Mv, and Sv have not changed significantly or decreased in most of the global ocean during 1979 to 2018. That is, wind energy is flat or more stable, while the monthly and seasonal variabilities tend to shrink/smooth, which is beneficial for wind energy utilization. (5) The Cv in the low-latitude Pacific and the Mv and Sv in both the North Indian and the low-latitude Pacific have an obvious abrupt phenomenon at the end of the 20th century.
The Morphological changes of basal channels based on multi-source remote sensing data at the Pine Island Ice Shelf
Xiangyu Song, Zemin Wang, Jianbin Song, Baojun Zhang, Mingliang Liu
 doi: 10.1007/s13131-023-2241-3
[Abstract](139) [FullText HTML](66) [PDF 2471KB](14)
The basal channel is a detailed morphological feature of the ice shelf caused by uneven basal melting. This kind of specifically morphology is widely distributed in polar ice shelves. It is an important research object of sea-ice interaction and plays a vital role in studying the relationship between the ice sheet/ice shelf and global warming. In this paper, high-resolution remote sensing image and ice penetration data were combined to extract the basal channel of the Pine Island ice shelf. The depth variation of Pine Island Ice Shelf in the recent 20 years was analyzed and discussed by using ICESat-1, ICESat-2, and IceBridge data. Combined with relevant marine meteorological elements (sea surface temperature, surface melting days, circumpolar deep water and wind) to analyze the basal channel changes, the redistribution of ocean heat is considered to be the most important factor affecting the evolution and development of the basal channel.
Observation of Arctic surface currents using data from a surface drifting buoy
Hongxia Chen, Lina Lin, Long Fan, Wangxiao Yang, Yinke Dou, Bingrui Li, Yan He, Bin Kong, Guangyu Zuo, Na Liu
 doi: 10.1007/s13131-023-2202-x
[Abstract](9) [FullText HTML](4)
During the 10th Chinese Arctic scientific expedition carried out in the summer of 2019, the surface current in the high-latitude areas of the Arctic Ocean was observed using a self-developed surface drifting buoy, which was initially deployed in the Chukchi Sea. The buoy traversed the Chukchi Sea, Chukchi Abyssal Plain, Mendeleev Ridge, Makarov Basin, and Canada Basin over a period of 632 d. After returning to the Mendeleev Ridge, it continued to drift toward the pole. Overall, the track of the buoy reflected the characteristics of the transpolar drift and Chukchi Slope Current, as well as the inertial flow, cross-ridge surface flow, and even the surface disorganized flow for some time intervals. The results showed that (1) the transpolar drift mainly occurs in the Chukchi Abyssal Plain, Mendeleev Ridge, and western Canada Basin to the east of the ridge where sea ice concentration is high, and the average northward flow velocity in the region between 79.41°N and 86.32°N was 5.1 cm/s; (2) the average surface velocity of the Chukchi Slope Current was 13.5 cm/s and, while this current moves westward along the continental slope, it also extends northwestward across the continental slope and flows to the deep sea; and (3) when sea ice concentration was less than 50%, the inertial flow was more significant (the maximum observed inertial flow was 26 cm/s, and the radius of the inertia circle was 3.6 km).
The influence of bioturbation on sandy reservoirs: the delta front sand of the lower Zhujiang Formation, Baiyun Depression, Zhujiang River Mouth Basin
Zhifeng Xing, Wei Wu, Juncheng Liu, Yongan Qi, Wei Zheng
 doi: 10.1007/s13131-022-2116-z
[Abstract](38) [FullText HTML](17) [PDF 5770KB](6)
Ichnofossils are well developed in clastic rock reservoirs in marine and transitional facies, which can considerably change the physical properties of the reservoir. However, this influence is not well understood, raising an important problem in the effective development of petroleum reservoirs. This paper analyzes continental shelf margin delta reservoirs through core observation, cast thin section observation and reservoir physical property test. Some important scientific insights are obtained: (1) The presence of Cruziana ichnofacies, including Asterosoma, Ophiomorpha, Planolites, Skolithos, Thalassinoides, and other ichnofossils can be used to identify in subaqueous distributary channels, subaqueous levee, frontal sheet sand, abandoned river channels, crevasse channels, main channels and channel mouth bars. Considerable differences in the types of ichnofossils and the degree of bioturbation can be observed in the different petrofacies. (2) Ichnofossils and bioturbation play a complex role in controlling reservoir properties. The reservoir physical properties have the characteristics of a decrease–increase–decrease curve with increasing bioturbation degree. This complex change is controlled by the sediment mixing and packing of bioturbation and the diagenetic environment controlled by the ichnofossils. (3) Sea-level cycle changes affect the modification of the reservoir through sediment packing. Bioturbation weakens the reservoir’s physical property when sea level slowly rises and improves the reservoir's physical property when base level slowly falls.
Multi-proxy reconstructions of hydrological changes from continental shelf sediments in the northern South China Sea during the interval 9 200–6 200 cal a BP
Chao Huang, Xiaoxu Qu, Lihui Wang, Yuhan Xie, Yongyi Luo, Fajin Chen, Yin Yang
 doi: 10.1007/s13131-023-2155-0
[Abstract](99) [FullText HTML](40) [PDF 995KB](6)
Past hydroclimatic conditions in southern China are poorly constrained owing to the lack of high-resolution marine-sediment records. In this study, we present high-resolution geochemical and grain-size records of marine sediments from the coastal shelf of the northern South China Sea to investigate regional hydrological variations. Results suggest a warm and humid climate during the interval 9 200–7 600 cal a BP, followed by a cold and dry climate from 7 600 cal a BP to 6 500 cal a BP, and progressive humidification during the period 6 500–6 200 cal a BP. A prominent hydrological anomaly occurred during 7 600–6 500 cal a BP. This abrupt event corresponds closely to tropical Pacific and interhemispheric temperature gradients, suggesting that moisture variations in southern China may have been driven by interhemispheric and zonal Pacific temperature gradients via modulation of the intensity and location of the West Pacific subtropical high.
A case study of continental shelf waves in the northwestern South China Sea induced by winter storms in 2021
Junyi Li, Chen Zhou, Min Li, Quanan Zheng, Mingming Li, Lingling Xie
 doi: 10.1007/s13131-023-2150-5
[Abstract](52) [FullText HTML](19)
This study aims to investigate characteristics of continental shelf wave (CSW) on the northwestern continental shelf of the South China Sea (SCS) induced by winter storms in 2021. Mooring and cruise observations, tidal gauge data at stations Hong Kong (HK), Zhapo (ZP) and Qinglan (QL) and sea surface wind data from January 1 to February 28, 2021 are used to examine the relationship between along-shelf wind and sea level fluctuation. Two events of CSWs driven by the along-shelf sea surface wind are detected from wavelet spectra of tidal gauge data. The signals are triply peaked at periods of 56 h, 94 h and 180 h, propagating along the coast with phase speed ranging from 6.9 m/s to18.9 m/s. The dispersion relation shows their property of the Kelvin mode of CSW. We develop a simple method to estimate amplitude of sea surface fluctuation by along-shelf wind. The results are comparable with the observation data, suggesting it is effective. The mode 2 CSWs fits very well with the mooring current velocity data. The results from rare current help to understand wave-current interaction in the northwestern SCS.
Mixed layer warming by the barrier layer in the southeastern Indian Ocean
Kaiyue Wang, Yisen Zhong, Meng Zhou
 doi: 10.1007/s13131-023-2151-4
[Abstract](59) [FullText HTML](28)
The southeastern Indian Ocean is characterized by the warm barrier layer (BL) underlying the cool mixed layer water in austral winter. This phenomenon lasts almost half a year and thus provides a unique positive effect on the upper mixed layer heat content through the entrainment processes at the base of the mixed layer, which has not been well evaluated due to the lack of proper method and dataset. Among various traditional threshold methods, here we show that the 5 m fixed depth difference can produce a reliable and accurate estimate of the entrainment heat flux (EHF) in this BL region. The comparison between the daily and monthly EHF warming indicates that the account for high-frequency EHF variability almost doubles the warming effect in the BL period, which can compensate for or even surpass the surface heat loss. This increased warming is a result of stronger relative rate of the mixed layer deepening and larger temperature differences between the mixed layer and its immediate below in the daily-resolving data. The interannual EHF shows a moderately increasing trend and similar variabilities to the Southern Annular Mode (SAM), likely because the mixed layer deepening under the positive SAM trend is accompanied by enhanced turbulent entrainment and thus increases the BL warming.
Strip segmentation of oceanic internal waves in SAR images based on TransUNet
Kaituo Qi, Jiaojiao Lu, Hongsheng Zhang, Yinggang Zheng, Zhouhao Zhang
 doi: 10.1007/s13131-023-2206-6
[Abstract](202) [FullText HTML](91)
The development of oceanic remote sensing artificial intelligence has made possible to obtain valuable information from amounts of massive data. Oceanic internal waves play a crucial role in oceanic activity. To obtain oceanic internal wave stripes from synthetic aperture radar (SAR) images, a stripe segmentation algorithm is proposed based on the TransUNet framework, which is a combination of U-Net and Transformer, which is also optimized. Through adjusting the number of Transformer layer, MLP channel, and Dropout parameters, the influence of over-fitting on accuracy is significantly weakened, which is more conducive to segmenting lightweight oceanic internal waves. The results show that the optimized algorithm can accurately segment oceanic internal wave stripes. Moreover, the optimized algorithm can be trained on a microcomputer, thus reducing the research threshold. The proposed algorithm can also change the complexity of the model to adapt it to different date scales. Therefore, TransUNet has immense potential for segmenting oceanic internal waves.
Simulated Indonesian Throughflow in Makassar Strait across the SODA3 products
Tengfei Xu, Zexun Wei, Haifeng Zhao, Shen Guan, Shujiang Li, Guanlin Wang, Fei Teng, Yongcui Zhang, Jing Wang
 doi: 10.1007/s13131-023-2186-6
[Abstract](247) [FullText HTML](104)
The Indonesian Throughflow (ITF), which connects the tropical Pacific and Indian Oceans, plays important roles in the inter-ocean water exchange and regional or even global climate variability. The Makassar Strait is the main inflow passage of the ITF, carrying about 77% of the total ITF volume transport. In this study, we analyze the simulated ITF in the Makassar Strait in the Simple Ocean Data Assimilation version 3 (SODA3) datasets. A total of nine ensemble members of the SODA3 datasets, of which are driven by different surface forcings and bulk formulas, and with or without data assimilation, are used in this study. The annual mean water transports (i.e., volume, heat and freshwater) are related to the combination of surface forcing and bulk formula, as well as whether data assimilation is employed. The phases of the seasonal and interannual variability in water transports cross the Makassar Strait, are basically consistent with each other among the SODA3 ensemble members. The interannual variability in Makassar Strait volume and heat transports are significantly correlated with El Niño-Southern Oscillation (ENSO) at time lags of −6 to 7 months. There is no statistically significant correlation between the freshwater transport and the ENSO. The Makassar Strait water transports are not significantly correlated with the Indian Ocean Dipole (IOD), which may attribute to model deficiency in simulating the propagation of semi-annual Kelvin waves from the Indian Ocean to the Makassar Strait.
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](63) [FullText HTML](29)
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.
Technical development of operational in-situ marine monitoring and research on its key generic technologies in China
Yunzhou Li, Juncheng Wang
 doi: 10.1007/s13131-023-2207-5
[Abstract](73) [FullText HTML](27)
In China, operational in-situ marine monitoring is the primary means of directly obtaining hydrological, meteorological, and environmental parameters across sea areas, and it is essential for applications such as forecast of marine environment, prevention and mitigation of disaster, exploitation of marine resources, marine environmental protection, and management of transportation safety. In this paper, we summarise the composition, development courses, and present operational status of three systems of operational in-situ marine monitoring, namely Coastal Marine Automated Network station, ocean data buoy and Voluntary Observing Shipmeasuring and reporting system. Additionally, we discuss the technical development in these in-situ systems and achievements in the key generic technologies along with future development trends.
Regeneration and anti-migration of sand waves associated with sand mining in the Taiwan Shoal
Jingjing Bao, Feng Cai, Chengqiang Wu, Huiquan Lu, Yongling Zheng, Yufeng Li, Li Sun, Chungeng Liu, Yongbao Li
 doi: 10.1007/s13131-023-2162-1
[Abstract](73) [FullText HTML](35)
Sand waves in the Taiwan Shoal are characterized by two distinct spatial scales. Giant sand waves have a length of two kilometers with height between 5 m and 25 m, whilst small sand waves is less than 100-m long with height less than 5 m between giant sand wave peaks (crests). A series of five high-resolution multi-beam echo-sounding surveys between 2012 and 2020 in the middle of Taiwan Shoal indicated that artificial dredging on the giant sand waves had caused sand wave reform and evolution. Overall, the removal of giant sand waves significantly affected the migration of small sand waves adjacent to the dredging site, with the latter on both sides of the former appear to migrate towards the dredging pit. Moreover, in the dredging area, new sand waves emerged with wavelength much smaller than the original giant sand waves, while the convergent pattern of the small sand waves tend store form the giant sand waves, which might spread far beyond the survey period.
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](59) [FullText HTML](28)
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.
Study on strength properties and soil behaviour type classification of Yellow River Delta silts based on variable rate piezocone penetration test
Yunuo Liu, Guoqing Lin, Yan Zhang, Shenggui Deng, Lei Guo, Tao Liu
 doi: 10.1007/s13131-022-2113-2
[Abstract](25) [FullText HTML](10)
Fine-grained silt is widely distributed in the Yellow River Delta (YRD) in China, and the sedimentary structure is complex, meaning that the clay content in the silt is variable. The piezocone penetration test (CPTu) is the most widely approved in situ test method. It can be used to invert soil properties and interpret soil behavior. To analyse the strength properties of surface sediments in the Yellow River Delta, this paper evaluated the friction angle and its inversion formula through the CPTu penetration test and monotonic simple shear test and other soil unit experiments. The evaluation showed that the empirical formula proposed by Kulhawy and Mayne had better prediction and inversion effect. The Yellow River Delta silts (YRD silts) with clay contents of 9.2 %, 21.4 % and 30.3% were selected as samples for the CPTu variable rate penetration test. The results show that: (1) The effects of the clay content on the tip resistance and the pore pressure of silt under different penetration rates were summarized. The tip resistance \begin{document}$ {Q}_{t} $\end{document} is strongly dependent on the clay content of the silt, the \begin{document}$ {B}_{q} $\end{document} value of the silt tends to 0 and is not significantly affected by the change of the CPTu penetration rate. (2) Five soil behavior type classification charts and three soil behavior type indexes based on CPTu data were evaluated. The results show that the soil behavior type classification chart based on soil behavior type index \begin{document}$ {I}_{SBT} $\end{document}, the Robertson 2010 behavior type classification chart are more suitable for the silty soil in the Yellow River Delta.
Influence of asymmetric tidal mixing on sediment dynamics in a partially mixed estuary
Zhongyong Yang, Zhiming Liang, Yufeng Ren, Daobin Ji, Hualong Luan, Changwen Li, Yujie Cui, Andreas Lorke
 doi: 10.1007/s13131-023-2159-9
[Abstract](45) [FullText HTML](20)
To investigate the influence of asymmetric tidal mixing (ATM) on sediment dynamics in tidal estuaries, we developed a vertically one-dimensional idealized analytical model, in which the M2 tidal flow, residual flow and suspended sediment concentration (SSC) are described. Model solutions are obtained in terms of tidally-averaged, and tidally-varying components (M2 and M4) of both hydrodynamics and sediment dynamics. The effect of ATM was considered with a time-varying eddy viscosity and time-varying eddy diffusivity of SSC. For the first time, an analytical solution for SSC variation driven by varying diffusivity could be derived. The model was applied to York River estuary, where higher (or lower) eddy diffusivity was observed during flood (or ebb) in a previous study. The model results agreed well with the observation in both hydrodynamics and sediment dynamics. The vertical sediment distribution under the influence of ATM was analyzed in terms of the phase lag of the M2 component of SSC relative to tidal flow. The phase lag increases significantly in estuaries with typical ATM (higher diffusivity during flood and lower diffusivity during ebb) for the case of seaward-directed net bottom shear stress (e.g., strong river discharge). In contrary, the phase lag is reduced by ATM, if the tidally-averaged bottom shear stress is landward (e.g., strong horizontal density gradient). The dynamics of sediment transport was analyzed as a function of ATM phase lag to identify the time of highest sediment diffusivity, as well as a function of the residual flow, to evaluate the relative importance of seaward and landward residual flows. In estuaries with relative strong fresh water discharge or weak tidal forcing (in case of flood season or neap tide), the near bottom SSC could be higher during ebb than during flood, since the bottom shear stress is higher during ebb due to seaward residual flow. However, landward net sediment transport can be expected in these estuaries in case of a typical ATM, because higher diffusivity causes higher SSC and landward transport during the flood period, while both SSC and seaward transport could be lower during ebb. On the contrary, seaward sediment transport can be expected in estuaries with landward tidally mean bottom shear stress in case of a reverse ATM, where sediment diffusivity is higher during the ebb.
Morphometric analysis of the Andaman outer shelf and upper slope – Implications for the recent slope failure events
Pachoenchoke Jintasaeranee, Anond Snidvongs
 doi: 10.1007/s13131-023-2154-1
[Abstract](157) [FullText HTML](73)
The devastating 2004 tsunamis that hit the southwestern coast of Thailand pose a serious threat to people along the coastal zone. A major aim for the tsunami hazard prediction is better prediction of the next tsunamis and their impacts. In this paper, we present the first implications of recent slope failure events of the Andaman outer shelf and upper slope based on a new detailed bathymetric data and subbottom profiler records acquired during two cruises of the MASS project in 2006 and 2007. Morphometric analysis reveals a variety of anomalous features, including: three large plateaus surrounded by moats, ruggedness and unevenness of slope morphology, and two translational submarine landslides. Two submarine landslides are studied from the detailed bathymetric data and subbottom profiler record covering the upper slope of the Andaman Sea shelf break within Thai EEZ. Maximum approximated volumes of both displaced masses are 4.8×107 m3 and 2.2×107 m3. Considering the data, there is no evidence that landslides have been the sources for tsunami hazard potential in recent geological time. These prerequisites will allow better study of slope failure events in the area. Further investigation is required to better understand obvious geotectonic phenomena.
Vertical microbial profiling of water column reveals prokaryotic communities and distribution features of Antarctic Peninsula
Jiang Li, Luying Zhao, Xiaoqian Gu, Chengxuan Li, Qian Zhang, Liping Fu, Ao Zhang
 doi: 10.1007/s13131-023-2160-3
[Abstract](40) [FullText HTML](18)
Prokaryotic diversity and community composition in the water column of eight stations (63 samples) around the Antarctic Peninsula of the Southern Ocean were investigated. Through pyrosequencing of the V3–V4 hypervariable regions of the 16S ribosomal RNA gene, we characterized 4 720 089 valid reads representing 48 188 operational taxonomic units (OTUs, 97% similarity). The community was dominated by the phyla Pseudomonadota (original name: Proteobacteria, 47%), Oxyphotobacteria (26%), and Bacteroidota (original name: Bacteroidetes, 18%), which comprised an average of 91% of the total OTUs in all samples. The prokaryotic community composition varied vertically within the water column. Water column prokaryotic communities exhibited a clear depth profile, with higher microbial richness and higher diversity observed with increasing water depth. Cluster analysis of the community composition of water column samples exhibited a similar trend with depth. Correlation with environmental factors suggested distinct variation in prokaryotic community composition with change in depth, salinity, temperature and dissolved oxygen (DO) levels. Functional prediction showed presence of active nitrogen, sulphur and methane metabolic cycles along the vertical transect of the studied region. These results will improve our knowledge of prokaryotic diversity and community composition at different depth water column for better understanding of the microbial ecology and nutrient cycles in Antarctic Peninsula region of the Southern Ocean.
Prokaryotic diversity and community composition in the surface sediments of the Changjiang River Estuary in Summer
Changfeng Qu, Xixi Wang, Liping Zhang, Huamao Yuan, Xuegang Li, Ning Li, Fushan Chen, Jinlai Miao
 doi: 10.1007/s13131-023-2153-2
[Abstract](42) [FullText HTML](19)
Microorganisms are fundamental for the functioning of marine ecosystems and are involved in the decomposition of organic matter, transformation of nutrients and circulation of biologically-important chemicals. Based on the complexity of the natural geographic characteristics of the Changjiang River Estuary, the geographic distribution of sedimentary microorganisms and the causes of this distribution are largely unexplored. In this work, the surface sediment samples from the adjacent sea area of the Changjiang River Estuary were collected. Their prokaryotic diversity was examined by high-throughput sequencing (HTS) technology, and the environmental factors of the bacterial community were investigated. The results indicated that the distribution of prokaryotic communities in the sediments of the study areas showed obvious spatial heterogeneity. The sampling sequences divided the sample regions into three distinct clusters. Each geographic region had a unique community structure, although Proteobacteria, Bacteroidota, Desulfobacterota, Acidobacteriota, and Actinobacteriota all existed in these three branches. Canonical correspondence analysis demonstrated that prokaryotic diversity and community distribution were significantly correlated with the geographic location of sediment, seawater depth, and in particular, nutrient content (e.g., total phosphorus, total organic carbon and dissolved oxygen). Moreover, it was found for the first time that the metal ions obviously affected the composition and distribution of the prokaryotic community in this area. In general, this work provides new insights into the structural characteristics and driving factors of prokaryotic communities under the background of the ever-changing Changjiang River Estuary.
Significant wave height forecasts integrating ensemble empirical mode decomposition with sequence-to-sequence model
Lina Wang, Yu Cao, Xilin Deng, Huitao Liu, and Changming Dong
 doi: 10.1007/s13131-023-2246-y
[Abstract](69) [FullText HTML](31)
As wave height is an important parameter in marine climate measurement, its accurate prediction is crucial in ocean engineering. It also plays an important role in marine disaster early warning and ship design, etc. However, challenges in the large demand for computing resources and the improvement of accuracy are currently encountered. To resolve the above mentioned problems, sequence-to-sequence deep learning model (Seq-to-Seq) is applied to intelligently explore the internal law between the continuous wave height data output by the model, so as to realize fast and accurate predictions on wave height data. Simultaneously, ensemble empirical mode decomposition (EEMD) is adopted to reduce the non-stationarity of wave height data and solve the problem of modal aliasing caused by empirical mode decomposition (EMD), and then improves the prediction accuracy. A significant wave height forecast method integrating EEMD with the Seq-to-Seq model (EEMD-Seq-to-Seq) is proposed in this paper, and the prediction models under different time spans are established. Compared with the long short-term memory model, the novel method demonstrates increased continuity for long-term prediction and reduces prediction errors. The experiments of wave height prediction on four buoys show that the EEMD-Seq-to-Seq algorithm effectively improves the prediction accuracy in short-term (3-, 6-, 12-, and 24-h forecast horizon) and long-term (48-, and 72-h forecast horizon) predictions.
Distribution pattern of macrobenthic assemblages along a salinity gradient in Hangzhou Bay and adjacent waters
Runxuan Yan, Xiaobo Wang, Songyao Peng, Qingxi Han
 doi: 10.1007/s13131-022-2119-9
[Abstract](58) [FullText HTML](28)
It is widely acknowledged that the distribution of macrobenthos is affected by salinity, but the degree of influence varies in different areas. To explore the distribution pattern of macrobenthic assemblages in Hangzhou Bay, 12 stations were sampled to collect macrobenthos and the corresponding bottom water. Changes in the general characteristics of macrobenthos along the salinity gradient in Hangzhou Bay and the adjacent waters were considered. Three dominant species were identified, including the polychaetes Sternaspis chinensis, the crustacea Oratosquilla oratoria and the echinoderm Ophiura kinbergi. And the macrobenthic assemblages showed a zonal distribution along with the salinity change. The correlation analyses showed that salinity, depth, temperature, suspended solids and dissolved oxygen had concurrent significant correlations with carnivorous group, Margalef species richness (d), Brillouin index (H) and Shannon-Wiener diversity index (H’). In light of the strong correlation between salinity and Changjiang diluted water, which produces considerable disturbances by freshwater inflows, the deposition of suspended solids and the resuspension of seabed sediments, the combined environmental disturbances, instead of salinity alone, should be adopted to explain the zonation distribution pattern of macrobenthic assemblages.
Predictability of the upper ocean heat content in a CESM ensemble prediction system
Ting Liu, Wenxiu Zhong
 doi: 10.1007/s13131-023-2239-x
[Abstract](67) [FullText HTML](29)
Upper ocean heat content (OHC) has been widely recognized as a crucial precursor to high-impact climate variability, especially for that being indispensable to the long-term memory of the ocean. Assessing the predictability of OHC using state-of-the-art climate models is invaluable for improving and advancing climate forecasts. Recently developed retrospective forecast experiments, based on a Community Earth System Model ensemble prediction system, offer a great opportunity to comprehensively explore OHC predictability. Our results indicate that the skill of actual OHC predictions varies across different oceans and diminishes as the lead time of prediction extends. The spatial distribution of the actual prediction skill closely resembles the corresponding persistence skill, indicating that the persistence of OHC serves as the primary predictive signal for its predictability. The decline in actual prediction skill is more pronounced in the Indian and Atlantic Oceans than in the Pacific Ocean, particularly within tropical regions. Additionally, notable seasonal variations in the actual prediction skills across different oceans align well with the phase-locking features of OHC variability. The potential predictability of OHC generally surpasses the actual prediction skill at all lead times, highlighting significant room for improvement in current OHC predictions, especially for the North Indian Ocean and the Atlantic Ocean. Achieving such improvements necessitates a collaborative effort to enhance the quality of ocean observations, develop effective data assimilation methods, and reduce model bias.
Coral records of Mid-Holocene sea-level highstands and climate responses in the northern South China Sea
Yuanfu Yue, Lichao Tang, Kefu Yu, Rongyong Huang
 doi: 10.1007/s13131-023-2264-9
[Abstract](1011) [FullText HTML](499)
High-resolution sea-level data and high-precision dating of corals in the northern South China Sea (SCS) during the Holocene provide a reference and historical background for current and future sea-level changes and a basis for scientific assessment of the evolutionary trend of coral reefs in the SCS. Although sporadic studies have been performed around Hainan Island in the northern SCS, the reconstructed sea level presents different values or is controversial because the indicative meaning of the sea-level indicators were neither quantified nor uniform criteria. Here, we determined the quantitative relationship between modern living coral and sea level by measuring the top surfaces of 27 live Porites corals from the inner reef flat along the east coast of Hainan Island and assessed the accuracy of results obtained using coral as sea-level indicators. Additionally, three in situ fossil Porites corals were analyzed based on elevation measurements, digital X-Ray radiography, and U-Th dating. The survey results showed that the indicative meanings for the modern live Porites corals is (−146.09 ± 8.35) cm below the mean tide level (MTL). It suggested that their upward growth limit is constrained by the sea level, and the lowest low water is the highest level of survival for the modern live Porites corals. Based on the newly defined indicative meanings, 6 new sea-level index points (SLIPs) were obtained and 19 published SLIPs were recalculated. Those SLIPs indicated a relative sea level fluctuation between (227.7 ± 9.8) cm to (154.88 ± 9.8) cm MTL between (5 393 ± 25) cal a BP and (3 390 ± 12) cal a BP, providing evidences of the Mid-Holocene sea-level highstand in the northern SCS. Besides that, our analysis demonstrated that different sea-level histories may be produced based on different indicative meanings or criteria. The dataset of 276 coral U-Th ages indicates that coral reef development in the northern SCS comprised the initial development, boom growth, decline, and flourishing development again. A comparison with regional records indicated that synergistic effects of climatic and environmental factors were involved in the development of coral reefs in the northern SCS. Thus, the cessation of coral reef development during the Holocene in the northern SCS was probably associated with the dry and cold climate in South China, as reflected in the synchronous weakening of the ENSO and East Asian summer monsoon induced by the reduction of the 65°N summer insolation, which forced the migration of the Intertropical Convergence Zone.
Geological context and vents morphology in the ultramafic-hosted Tianxiu field, Carlsberg Ridge
Jin Liang, Chunhui Tao, Xiangxin Wang, Cheng Su, Wei Gao, Yadong Zhou, Weikun Xu, Xiaohe Liu, Zhongjun Ding
 doi: 10.1007/s13131-023-2157-y
[Abstract](55) [FullText HTML](25)
The Tianxiu hydrothermal field (TXHF) located on Carlsberg Ridge is one of the few active ultramafic-hosted venting systems known in the Indian Ocean. Despite numerous investigations, there is limited understanding of its sulfide structure morphology, and the factors controlling the formation of TXHF are poorly understood. In this study, we conducted detailed seafloor mapping using visual data obtained by dives using the human-occupied vehicle Jiaolong. The TXHF is found to be an active, off-axis, ultramafic-hosted, high-temperature hydrothermal area in which serpentine peridotite is exposed. Two main hydrothermal sites were identified, i.e., P and Y, both of which feature a complex of chimneys and beehive diffusers constituting a “chimney jungle” and isolated large steep-sided structures developed on flat-lying sulfide mounds. In addition, some sporadic inactive chimneys and outcrops of hydrothermal deposits were noted. The chimneys are rich in Fe and Zn sulfide, and lack the central fluid channel formed by focused high-temperature fluid flow. Hydrothermal venting at TXHF is likely related to low-angle detachment faults that focus and transport hydrothermal fluids away from a heat source along the valley wall. Our results complement and expand upon previous works concerning sulfide chimney morphology and their corresponding mineral paragenesis in ultramafic-hosted hydrothermal systems in the Indian Ocean and further our understanding of modern seafloor hydrothermal systems.
Molecular quantification of copepod Acartia erythraea feeding on different algae preys
Simin Hu, Tao Li, Hui Huang, Sheng Liu
 doi: 10.1007/s13131-022-2115-0
[Abstract](20) [FullText HTML](8)
Quantitative evaluation of the copepod feeding process is critical for understanding the functioning of marine food webs, as this provides a major link between primary producers and higher trophic levels. In this study, a molecular protocol based on quantitative polymerase chain reaction (qPCR) targeting 18S rDNA was developed and used to investigate the feeding and digestion rates of the copepod Acartia erythraea in a laboratory experiment using microalgae Thalassiosira weissflogii, Prorocentrum shikokuense, and Alexandrium catenella as prey. Although offered an equal encounter rate based on biovolume, prey uptake varied substantially among the three algal species, with the ingestion rate (IR) and digestion rate (DR) of A. erythraea differing significantly (P<0.001) based on both cell counting and qPCR detection. Acartia erythraea showed the highest IR (2.79×104 cells/(ind·h)) and DR (2.43×104 cells/(ind·h)) on T. weissflogii, and the lowest amounts of ingested P. shikokuense were detected. The highest assimilation rate (~90.64%, IR/DR) was observed in copepods fed with P. shikokuense. The qPCR method used here can help determine the digestion rate and assimilation rate of copepods by detecting cells remaining in the gut hence providing the possibility to examine trophic links involving key species in the marine ecosystem. Our results indicate that A. erythraea has diet-specific feeding performance in different processes, and a quantitative assessment of copepod feeding is needed to accurately determine its functional role in the energy and matter uptake from marine food webs.
Effects of main ecological factors on the growth of marine green alga Caulerpa sertularioides using the response surface methodology
Bingxin Huang, Yue Chu, Rongjuan Wang, Yixiao Wang, Lanping Ding
 doi: 10.1007/s13131-023-2171-0
[Abstract](22) [FullText HTML](8)
Caulerpa sertularioides is an invasive potential blooming green alga in China but it remains poorly studied. We studied the effects of ecological factors on its growth. Optimum conditions of ecological factors, i.e., irradiance, temperature, and salinity, for the growth of its fragments were determined in the response surface methodology (RSM). The specific growth rates (SGR) of the fragments were determined in single-factor experiment. The results show that the SGR of C. sertularioides peaked under the conditions of irradiance 37.5 μmol/(m2·s), temperature 25℃, and salinity 30. Meanwhile, using the Box-Behnken design, the conditions were further optimized and verified to be: irradiance 39.03 μmol/(m2·s), temperature 25.29℃, and salinity 30.06, under which the SGR reached 4.66%. The results provide new theoretical data and solutions for the cultivation, invasion prediction, and monitoring of Caulerpa species in China and the world. The RSM method may have great potential applications in the environmental adaptation characteristics of new macroalgal cultivars, intensive orientation cultured germplasm, and environmental hazard analysis of cultivated species in the field.
Two-stage reproduction derived from cells of thallus could directly contribute to seeds for green tidal algal Enteromorpha(Ulva) prolifera/clathrata bloom, with disclosure of their ephemeral trait
Bingxin Huang, Lanping Ding, Yao Zhang, Youxuan Guo, Junxia Liang, Yanqi Xie, Yue Chu
 doi: 10.1007/s13131-023-2158-x
[Abstract](34) [FullText HTML](17)
Green tidal alga Enteromorpha species complete their life cycles by the isomorphic alternation of generations. The provenance of green tide caused by them in the western Yellow Sea has been disputed. The cell reproduction derived from adult thallus was observed on E. clathrata collected from Shantou, Guangdong Province in this study. Subsequently, it further found that E. proliferia collected from Qingdao, Shandong Province and Qinhuangdao, Hebei Province, produced reproductive cells by somatic cells of its early infantile thallus or branch. The latter is functionally similar to that the seedlings of red alga Porphyra yezoensis produce the monospores, and could exquisitely explain the ephemeral or opportunistic trait and environmental adaptation ability of Enteromorpha species. Changes in growth conditions may induce the two types of cell reproduction. They contribute to the bloom, and can effectively reveal the seasonally occurring large-scale and on-year and off-year phenomenon. The latter may have played a decisive role in its formation. This paper analyses the legal status of the species name, the type of generation during bloom, ephemeral traits, the role of microscopic propagule, the area of origin, on-year and off-year phenomenon, early warning and prevention and control of the species, and so on. On this basis, further study on the influence of environmental factors on cell reproduction of early infantile thalli or branches will achieve a positive effect for early warning and prevention and control of the green tidal algal bloom.
Sedimentary evolution and control factors of the Rizhao Canyons in the Zhongjiannan Basin, western South China Sea
Meijing Sun, Yongjian Yao, Weidong Luo, Jie Liu, Xiaosan Hu, Jiao Zhou, Dong Ju, Ziying Xu
 doi: 10.1007/s13131-022-2114-1
[Abstract](36) [FullText HTML](15)
Submarine Canyon is an important channel for long-distance sediment transport, and an important part of deep-water sedimentary system. The Large-scale Rizhao canyons have been discovered for the first time in 2015 in the continental slope area of the western South China Sea. Based on the interpretation and analysis of multi-beam bathymetry and two-dimensional multi-channel seismic data. The geology of the canyons has however not been studied yet. In this paper, the morphology and distribution characteristics of the canyon are carefully described, the sedimentary filling structure and its evolution process of the canyon are analyzed, and then its controlling factors are discussed. The results show that Rizhao Canyon group is a large slope restricted Canyon group composed of one east-west main and nine branches extending to the south. The canyon was formed from the late Miocene to the Quaternary. The east-west main Canyon is mainly formed by the scouring and erosion of the material source from the west to the transition zone between the northern bench belt and the south slope of Zhongjiannan along the slope direction. Its development and evolution is mainly controlled by sediment supply and topographic conditions, the development of 9 branch canyons is mainly controlled by gravity flow and collapse from the East-West main canyon. This understanding result is a supplement to the study of “source -channel –sink” sedimentary system in the west of the South China Sea, and has important guiding significance for the study of marine geological hazards.
Satellite-observed significant improvement in nearshore transparency of the Bohai Sea during past 20 years
Xuyan Li, Jinzhao Xiang, Liudi Zhu, Zhibin Yang, Ting Wei, Bing Mu, Xiaobo Zhang, Tingwei Cui
 doi: 10.1007/s13131-023-2180-z
[Abstract](194) [FullText HTML](76)
The Bohai Sea (BS) is the unique semi-closed inland sea of China, characterized by degraded water quality due to significant terrestrial pollution input. In order to improve its water quality, a dedicated action named “Uphill Battles for Integrated Bohai Sea Management” (UBIBSM, 2018–2020) was implemented by the Chinese government. To evaluate the action effectiveness toward water quality improvement, variability of the satellite-observed water transparency (Secchi disk depth, ZSD) was explored, with special emphasis on the nearshore waters (within 20 km from the coastline) prone to terrestrial influence. (1) Compared to the status before the action began (2011–2017), majority (87.3%) of the nearshore waters turned clear during the action implementation period (2018–2020), characterized by the elevated ZSD by 11.6%±12.1%. (2) Nevertheless, the improvement was not spatially uniform, with higher ZSD improvement in provinces of Hebei, Liaoning, and Shandong (13.2%±16.5%, 13.2%±11.6%, 10.8%±10.2%, respectively) followed by Tianjin (6.2%±4.7%). (3) Bayesian trend analysis found the abrupt ZSD improvement in April 2018, which coincided with the initiation of UBIBSM, implying the water quality response to pollution control. More importantly, the independent statistics of land-based pollutant discharge also indicated that the significant reduction of terrestrial pollutant input during the UBIBSM action was the main driver of observed ZSD improvement. (4) Compared with previous pollution control actions in the BS, UBIBSM was found to be the most successful one during the past 20 years, in terms of transparency improvement over nearshore waters. The presented results proved the UBIBSM-achieved remarkable water quality improvement, taking the advantage of long-term consistent and objective data record from satellite ocean color observation.
Prediction of seawater pH by bidirectional gated recurrent neural network with attention under phase space reconstruction: case study of the coastal waters of Beihai
Chongxuan Xu, Ying Chen, Xueliang Zhao, Wenyang Song, Xiao Li
[Abstract](37) [FullText HTML](15)
Marine life is very sensitive to changes in pH. Even slight changes can cause ecosystems to collapse. Therefore, understanding the future pH of seawater is of great significance for the protection of the marine environment. At present, the monitoring method of seawater pH has been matured. However, how to accurately predict future changes has been lacking effective solutions. Based on this, the model of bidirectional gated recurrent neural network with multi-headed self-attention based on improved complete ensemble empirical mode decomposition with adaptive noise combined with phase space reconstruction (ICPBGA) is proposed to achieve seawater pH prediction. To verify the validity of this model, pH data of two monitoring sites in the Beihai coastal sea area are selected to verify the effect. At the same time, the ICPBGA model is compared with other excellent models for predicting chaotic time series, and root mean square error (RMSE), mean absolute error (MAE), mean absolute percentage error (MAPE), and coefficient of determination (R2) are used as performance evaluation indicators. The R2 of the ICPBGA model at site 1 and site 2 are above 0.9, and the prediction errors are also the smallest. The results show that the ICPBGA model has a wide range of applicability and the most satisfactory prediction effect. The prediction method in this paper can be further expanded and used to predict other marine environmental indicators.
Wave hindcast under tropical cyclone conditions in the South China Sea: sensitivity to wind fields
Liqun Jia, Shimei Wu, Bo Han, Shuqun Cai, Renhao Wu
 doi: 10.1007/s13131-023-2227-1
[Abstract](246) [FullText HTML](111)
Reliable wave information is critical for marine engineering. Numerical wave models are useful tools to obtain wave information with continuous spatiotemporal distributions. However, the accuracy of model results highly depends on the quality of wind forcing. In this study, we utilize observations from five buoys deployed in the northern South China Sea from August to September 2017. Notably, these buoys successfully recorded wind field and wave information during the passage of five tropical cyclones of different intensities without sustaining any damage. Based on these unique observations, we evaluated the quality of four widely used wind products, namely CFSv2, ERA5, CCMP, and ERAI. Our analysis showed that in the northern South China Sea, ERA5 performed best compared to buoy observations, especially in terms of maximum wind speed values at 10 m height (U10), extreme U10 occurrence time, and overall statistical indicators. CFSv2 tended to overestimate non-extreme U10 values. CCMP showed favorable statistical performance at only three of the five buoys, but underestimated extreme U10 values at all buoys. ERAI had the worst performance under both normal and tropical cyclone conditions. In terms of wave hindcast accuracy, ERA5 outperformed the other reanalysis products, with CFSv2 and CCMP following closely. ERAI showed poor performance especially in the upper significant wave heights. Furthermore, we found that the wave hindcasts did not improve with increasing spatiotemporal resolution, with spatial resolution up to 0.5°. These findings would help in improving wave hindcasts under extreme conditions.
Exploring spatial non-stationarity of near-miss ship collisions from AIS data under the influence of sea fog using geographically weighted regression: A case study in the Bohai Sea, China
Yongtian Shen, Zhe Zeng, Dan Liu, Pei Du
 doi: 10.1007/s13131-022-2137-7
[Abstract](135) [FullText HTML](48)
Sea fog is a disastrous weather phenomenon, posing a risk to the safety of maritime transportation. Dense sea fogs reduce visibility at sea and have frequently caused ship collisions. This study used a geographically weighted regression (GWR) model to explore the spatial non-stationarity of near-miss collision risk, as detected by a vessel conflict ranking operator (VCRO) model from automatic identification system (AIS) data under the influence of sea fog in the Bohai Sea. Sea fog was identified by a machine learning method that was derived from Himawari-8 satellite data. The spatial distributions of near-miss collision risk, sea fog, and the parameters of GWR were mapped. The results showed that sea fog and near-miss collision risk have specific spatial distribution patterns in the Bohai Sea, in which near-miss collision risk in the fog season is significantly higher than that outside the fog season, especially in the northeast (the sea area near Yingkou Port and Bayuquan Port) and the southeast (the sea area near Yantai Port). GWR outputs further indicated a significant correlation between near-miss collision risk and sea fog in fog season, with higher R-squared (0.890 in fog season, 2018), than outside the fog season (0.723 in non-fog season, 2018). GWR results revealed spatial non-stationarity in the relationships between-near miss collision risk and sea fog and that the significance of these relationships varied locally. Dividing the specific navigation area made it possible to verify that sea fog has a positive impact on near-miss collision risk.
Retrieval of snow depth on Antarctic sea ice from the FY-3D MWRI data
Zhongnan Yan, Xiaoping Pang, Qing Ji, Yizhuo Chen, Chongxin Luo, Pei Fan, Zeyu Liang
 doi: 10.1007/s13131-023-2179-5
[Abstract](178) [FullText HTML](74)
The snow depth on sea ice is an extremely critical part of the cryosphere. Monitoring and understanding changes of snow depth on Antarctic sea ice is beneficial for research on sea ice and global climate change. The Microwave Radiation Imager (MWRI) sensor aboard the Chinese FengYun-3D (FY-3D) satellite has great potential for obtaining information of the spatial and temporal distribution of snow depth on the sea ice. By comparing in-situ snow depth measurements during the 35th Chinese Antarctic Research Expedition (CHINARE-35), we took advantage of the combination of multiple gradient ratio (GR (36V, 10V) and GR (36V, 18V)) derived from the measured brightness temperature of FY-3D MWRI to estimate the snow depth. This method could simultaneously introduce the advantages of high and low GR in the snow depth retrieval model and perform well in both deep and shallow snow layers. Based on this, we constructed a novel model to retrieve the FY-3D MWRI snow depth on Antarctic sea ice. The new model validated by the ship-based observational snow depth data from CHINARE-35 and the snow depth measured by snow buoys from the Alfred Wegener Institute (AWI) suggest that the model proposed in this study performs better than traditional models, with root mean square deviations (RMSDs) of 8.59 cm and 7.71 cm, respectively. A comparison with the snow depth measured from Operation IceBridge (OIB) project indicates that FY-3D MWRI snow depth was more accurate than the released snow depth product from the U.S. National Snow and Ice Data Center and the National Tibetan Plateau Data Center. The spatial distribution of the snow depth from FY-3D MWRI agrees basically with that from ICESat-2; this demonstrates its reliability for estimating Antarctic snow depth, and thus has great potential for understanding snow depth variations on Antarctic sea ice in the context of global climate change.
Record of hydrothermal activity in the Yuhuang hydrothermal field and its implications for the Southwest Indian Ridge: evidence from sulfide chronology
Weifang Yang, Chunhui Tao, Shili Liao, Jin Liang, Wei Li, Teng Ding, Ágata Alveirinho Dias, Xuefeng Wang, Lisheng Wang
 doi: 10.1007/s13131-023-2194-6
[Abstract](108) [FullText HTML](45)
The Yuhuang hydrothermal field (YHF) is located between the Indomed and Gallieni fracture zones near the top of the off-axis slope on the south rift wall of Segment 29 on the ultraslow Southwest Indian Ridge (SWIR). Previous studies have shown that sulfides in the YHF formed during different mineralization episodes and the YHF has the greatest potential for the formation of large-scale seafloor massive sulfide deposits. However, the sulfide chronology and hydrothermal activity of the YHF remain poorly constrained. In this study, mineralogical analyses and 230Th/U dating were performed. Hydrothermal activity may start about (35.9±2.3) kyrs from the southwest part of the YHF and may cease about 708±81 years ago from the northeast part of the YHF. The 74 nonzero chronological data from hydrothermal sulfide samples provide the first quantitative characterization of the spatial and temporal history along the SWIR. Hydrothermal activity in the SWIR has been relatively active over the past 20 kyrs. In contrast, between 40 kyrs and 100 kyrs, hydrothermal activity was relatively infrequently and short in duration. The maximum activity occurred at 15–11 kyrs, 9–7 kyrs, 6–0.2 kyrs. There was a slight positive correlation between the maximal age and estimated surface area or estimated tonnage. The minimum mass accumulation rate of YHF is about 278 t/a, which is higher than most HFs related to ultramafic systems. The ultraslow spreading SWIR have the greatest potential to form large-scale SMS deposits. The results of this study provide new insights into the metallogenic mechanism of hydrothermal sulfides along ultraslow-spreading ridges.
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
 doi: 10.1007/s13131-023-2175-9
[Abstract](96) [FullText HTML](38)
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 seconds 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.
The Connection of Phytoplankton Biomass in the Marguerite Bay Polynya of the Western Antarctic Peninsula to the Southern Annular Mode
Ning Jiang, Zhaoru Zhang, Ruifeng Zhang, Chuning Wang, Meng Zhou
 doi: 10.1007/s13131-023-2201-y
[Abstract](191) [FullText HTML](76)
Antarctic coastal polynyas are biological hotspots in the Southern Ocean that support the abundance of high-trophic-level predators and are important for carbon cycling in the high-latitude oceans. In this study, we examined the interannual variation of summertime phytoplankton biomass in the Marguerite Bay polynya (MBP) in the western Antarctic peninsula area, and linked such variability to the Southern Annular Mode (SAM) that dominated the southern hemisphere extratropical climate variability. Combining satellite data, atmosphere reanalysis products and numerical simulations, we found that the interannual variation of summer chlorophyll-a concentration (Chl-a) in the MBP is significantly and negatively correlated with the spring SAM index, and weakly correlated with the summer SAM index. The negative relation between summer Chl-a and spring SAM is due to weaker spring vertical mixing under a more positive SAM condition, which would inhibit the supply of iron from deep layers into the surface euphotic layer. The negative relation between spring mixing and spring SAM results from greater precipitation rate over the MBP region in positive SAM phase, which leads to lower salinity in the ocean surface layer. The coupled physical-biological mechanisms between SAM and phytoplankton biomass revealed in this study is important for us to predict the future variations of phytoplankton biomasses in Antarctic polynyas under climate change.
Modeling wave attenuation by vegetation with accompanying currents in SWAN
Hong Wang, Zhan Hu
 doi: 10.1007/s13131-023-2199-1
[Abstract](158) [FullText HTML](70)
Coastal wetlands such as salt marshes and mangroves provide important protection against stormy waves. Accurate assessments of wetlands’ capacity in wave attenuation are required to safely utilize their protection services. Recent studies have shown that tidal currents have a significant impact on wetlands’ wave attenuation capacity, but such impact has been rarely considered in numerical models, which may lead to overestimation of wave attenuation in wetlands. This study modified the SWAN (Simulating Waves Nearshore) model to account for the effect of accompanying currents on vegetation-induced wave dissipation. Furthermore, this model was extended to include automatically derived vegetation drag coefficients, spatially varying vegetation height, and Doppler Effect in combined current-wave flows. Model evaluation against an analytical model and flume data shows that the modified model can accurately simulate wave height change in combined current-wave flows. Subsequently, we applied the new model to a mangrove wetland on Hailing Island in China with a special focus on the effect of currents on wave dissipation. It is found that the currents can either increase or decrease wave attenuation depending on the ratio of current velocity to the amplitude of the horizontal wave orbital velocity, which is in good agreement with field observations. Lastly, we used Hailing Island site as an example to simulate wave attenuation by vegetation under hypothetical storm surge conditions. Model results indicate that when currents are 0.08–0.15 m/s and the incident wave height is 0.75–0.90 m, wetlands’ wave attenuation capacity can be reduced by nearly 10% compared with pure wave conditions, which provides implications for critical design conditions for coastal safety. The obtained results and the developed model are valuable for the design and implementation of wetland-based coastal defense. The code of the developed model has been made open source, in the hope to assist further research and coastal management.
A VGGNet-based correction for satellite altimetry-derived gravity anomalies to improve the accuracy of bathymetry to depths of 6 500 m
Xiaolun Chen, Xiaowen Luo, Ziyin Wu, Xiaoming Qin, Jihong Shang, Huajun Xu, Bin Li, Mingwei Wang, Hongyang Wan
 doi: 10.1007/s13131-023-2203-9
[Abstract](136) [FullText HTML](51)
Understanding the topographic patterns of the seafloor is a very important part of understanding our planet. Although the science involved in bathymetric surveying has advanced much over the decades, less than 20% of the seafloor has been precisely modeled to date, and there is an urgent need to improve the accuracy and reduce the uncertainty of underwater survey data. In this study, we introduce a pretrained VGGNet method based on deep learning. To apply this method, we input gravity anomaly data derived from ship measurements and satellite altimetry into the model and correct the latter, which has a larger spatial coverage, based on the former, which is considered the true value and is more accurate. After obtaining the corrected high-precision gravity model, it is inverted to the corresponding bathymetric model by applying the gravity-depth correlation. We choose four data pairs collected from different environments, i.e., the Southern Ocean, Pacific Ocean, Atlantic Ocean and Caribbean Sea, to evaluate the topographic correction results of the model. The experiments show that the R2 reaches 0.834 among the results of the four experimental groups, signifying a high correlation. The standard deviation (SD) and normalized root mean square error (NRMSE) are also evaluated, and the accuracy of their performance improved by up to 24.2% compared with similar research done in recent years. The evaluation of the R2 values at different water depths shows that our model can achieve performance results above 0.90 at certain water depths and can also significantly improve results from mid-water depths when compared to previous research. Finally, the bathymetry corrected by our model is able to show an accuracy improvement level of more than 21% within 1% of the total water depths, which is sufficient to prove that the VGGNet-based method has the ability to perform a gravity-bathymetry correction and achieve outstanding results.
Gravity anomalies determined from mean sea surface model data over the Gulf of Mexico
Xuyang Wei, Xin Liu, Zhen Li, Xiaotao Chang, Hongxin Luo, Chengcheng Zhu, Jinyun Guo
 doi: 10.1007/s13131-023-2178-6
[Abstract](160) [FullText HTML](57)
With the improvements in the density and quality of satellite altimetry data, a high-precision and high-resolution mean sea surface model containing abundant information regarding a marine gravity field can be calculated from long-time series multi-satellite altimeter data. Therefore, in this study, a method is proposed for determining marine gravity anomalies from a mean sea surface model. Taking the Gulf of Mexico (15°–32°N, 80°–100°W) as the study area and using a removal-recovery method, the residual gridded deflections of the vertical (DOVs) are calculated by combining the mean sea surface, mean dynamic topography, and XGM2019e_2159 geoid, and then using the inverse Vening-Meinesz method to determine the residual marine gravity anomalies from the residual gridded DOVs. Finally, residual gravity anomalies are added to the XGM2019e_2159 gravity anomalies to derive marine gravity anomaly models. In this study, the marine gravity anomalies are estimated with mean sea surface models CNES_CLS15MSS, DTU21MSS, and SDUST2020MSS and the mean dynamic topography models CNES_CLS18MDT and DTU22MDT. The accuracy of the marine gravity anomalies derived by the mean sea surface model is assessed based on ship-borne gravity data. The results show that the difference between the gravity anomalies derived by DTU21MSS and CNES_CLS18MDT and those of the ship-borne gravity data is optimal. With an increase in the distance from the coast, the difference between the gravity anomalies derived by mean sea surface models and ship-borne gravity data gradually decreases. The accuracy of the difference between the gravity anomalies derived by mean sea surface models and those from ship-borne gravity data is optimal at a depth of 3–4 km. The accuracy of the gravity anomalies derived by the mean sea surface model is high.
Three-dimensional constrained gravity inversion of Moho depth and crustal structural characteristics at Mozambique continental margin
Shihao Yang, Zhaocai Wu, Yinxia Fang, Mingju Xu, Jialing Zhang, Fanlin Yang
 doi: 10.1007/s13131-023-2220-8
[Abstract](148) [FullText HTML](37)
Mozambique’s continental margin in East Africa was formed during the break-off stage of the east and west Gondwana lands. Studying the geological structure and division of continent-ocean boundary (COB) in Mozambique’s continental margin is considered of great significance to rebuild Gondwana land and understand its movement mode. Along these lines, in this work, the initial Moho was fit using the known Moho depth from reflection seismic profiles, and a 3D multi-point constrained gravity inversion was carried out. Thus, high-accuracy Moho depth and crustal thickness in the study area were acquired. According to the crustal structure distribution based on the inversion results, the continental crust at the narrowest position of the Mozambique Channel was detected. According to the analysis of the crustal thickness, the Mozambique ridge is generally oceanic crust and the COB of the whole Mozambique continental margin is divided.
Differences in Spring Precipitation over Southern China associated with Multiyear La Niña Events
Guangliang Li, Licheng Feng, Wei Zhuang, Fei Liu, Ronghua Zhang, Cuijuan Sui
 doi: 10.1007/s13131-023-2147-0
[Abstract](352) [FullText HTML](140)
Composite analyses were performed in this study to reveal the differences in spring precipitation over southern China during multiyear La Niña events from 1901-2015. It was found that there is significantly below normal precipitation in the first boreal spring, but above normal in the second year. The differences in spring precipitation over southern China are correlative to the changes in anomalous atmospheric circulations over the northwest Pacific, which can in turn be attributed to different anomalous sea surface temperatures (SSTs) over the tropical Pacific. During multiyear La Niña events, anomalous SSTs were stronger in the first spring than those in the second spring. As a result, the intensity of abnormal cyclones (WNPC) in the western North Pacific Ocean (WNP) in the first year is stronger, which is more likely to reduce moisture transport, leading to prolonged precipitation deficits over southern China. In contrast, the tropical SST signal is too weak to induce appreciable changes in the WNPC and precipitation over South China in the second year. The difference in SST signals in two consecutive springs leads to different spatial patterns of precipitation in southern China by causing different WNPC.
Forty-Year Investigation of Wave Power in Energetic Region of Persian Gulf in Iranian Territorial Waters by Using Short-Term and New Long-Term Stability Assessment Parameters
Fouad Salimi, Cyrus Ershadi, Vahid Chegini
 doi: 10.1007/s13131-022-2110-5
[Abstract](212) [FullText HTML](47)
The wave power in high potential area of the northern Persian Gulf (near to Iranian coastal areas) is assessed by taking into account the temporal and spatial distributions of wave power for a period of forty years. For this purpose, assimilated wind data of European Centre for Medium-Range Weather Forecasts (ECMWF) Interim Reanalysis (ERA-Interim), and hydrography data of GEBCO are used as SWAN model. Seven locations are investigated in the study area by considering the amount of Cv (Coefficient of variation), the amount of average annual power, and the short-term (MVI and SVI) and a new long-term (DVI) power stability assessment parameters. The results showed more stability in the eastern parts of the study area and concluded that a narrow line between the point which is in the middle and another point which is in the eastern middle part of the study area may be the best locations for more investigation and the feasibility study for energy converter farms. Also, it is found that the middle part of the study region with about 2.5 kW/m power is the most energetic area. It is concluded that the dominant direction of wave power distribution in all points is the north east and this dominant direction has not changed during the forty-year period. It is observed that the mean annual energy increases with a slight slope in the total 40 years and this increasing trend is more obvious in the fourth decade. Although it is observed that the wave power of the second decade has the most stability and the least variation, the wave power in the fourth decade has the most variation. Moreover, the results showed that the study region's wave power increase by approximately a mean change rate of 0.027 (kW/m.year) and the maximum change rate of wave power was in the northwest part and the minimum change rate of wave power was in the southeast part which were about 0.036 (kW/m.year) and 0.014 (kW/m.year) respectively.
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](151) [FullText HTML](47)
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](273) [FullText HTML](95)
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](600) [FullText HTML](175)
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.
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2023-8 Cover
2023, 42(8).  
[Abstract](42) [PDF 4047KB](8)
2023-8 Contents
2023, 42(8): .  
[Abstract](30) [FullText HTML](14) [PDF 62KB](3)
Distinguishing the main components of submarine groundwater and estimating the corresponding fluxes based on radium tracing method—taking the Maowei Sea for example
Linwei Li, Jinzhou Du, Xilong Wang, Yanling Lao
2023, 42(8): 1-23.   doi: 10.1007/s13131-023-2211-9
[Abstract](146) [FullText HTML](69) [PDF 2460KB](26)
Submarine groundwater discharge (SGD) is an important part in the land-sea interactions, which mainly contains three components: submarine fresh groundwater discharge (SFGD), tidal flat recirculated saline groundwater discharge (tidal flat RSGD) and subtidal recirculated saline groundwater discharge (subtidal RSGD). In order to make a more accurate assessment of the impact of SGD on coastal ecological environment, it is necessary to distinguish the main components of SGD. In this study, the Maowei Sea, located in the northern part of the Beibu Gulf, was selected as the study area. Based on the radium (Ra) tracing method, we present a new analytical method for distinguishing the three main components of SGD in this area combined with field data. The average daily flow along the coastline of the Maowei Sea of tidal flat RSGD was slightly higher than that of SFGD, and both two were on the magnitude of 1×105 m3/d. The average daily flow for the subtidal RSGD of the entire subtidal zone of the Maowei Sea reached to the magnitude of 1×106–1×107 m3/d. The long-term variation trend of terrestrial SGD is a valuable information for the study of the influence of terrigenous material on the coastal ecological environment. Based on the results of four sampling periods, it is found that the fluxes of SFGD and tidal flat RSGD in the Maowei Sea had good linear correlation with the net precipitation. As an example, January 2015 to August 2022 were selected as the study periods, and the variation trends of SFGD and tidal flat RSGD were calculated by linear function with net precipitation as the independent variable. The results showed that the flux of tidal flat RSGD was slightly higher than that of SFGD, and the difference between the two is larger in flood season while smaller in dry season. In general, in the coastal range of China, the total SGD flux in the Maowei Sea area is at a high level, and the SFGD flux is at a medium level.
Using radium isotopes to evaluate the uncertainty of submarine groundwater discharge in the northeast and entirety of Daya Bay
Hequan Gu, Feng Zhao, Zhixin Ni, Meigui Wu, Li Zhao, Aicui Dang, Dongmei Li, Minxia Zhang, Qin Hu
2023, 42(8): 24-31.   doi: 10.1007/s13131-023-2181-y
[Abstract](117) [FullText HTML](50) [PDF 1065KB](13)
Submarine groundwater discharge (SGD), which can be traced using naturally occurring radium isotopes, has been recognized as a significant nutrient source and land-ocean interaction passage for the coastal waters of the Daya Bay, China. However, uncertainties in assessing SGD fluxes must still be discussed in detail. In this study, we attempted to utilize the Monte Carlo method to evaluate the uncertainties of radium-derived SGD flux in the northeast and entirety of the Daya Bay. The results show that the uncertainties of the SGD estimate in the northeast bay are very sensitive to variations in excess radium inventories as well as radium inputs from bottom sediments, while the uncertainties of the SGD estimate for the entire bay are strongly affected by fluctuations in radium inputs from bottom sediments and radium end-members of SGD. This study will help to distinguish the key factors controlling the accuracy of SGD estimates in similar coastal waters.
Using radium isotopes to quantify submarine groundwater discharge at different scales in the Huanghe River Estuary, China
Haowei Xu, Disong Yang, Xiaoyi Guo, Maosheng Gao, Guangquan Chen, Diansheng Ji, Shengtao Chen, Huaming Yu, Bochao Xu
2023, 42(8): 32-39.   doi: 10.1007/s13131-023-2236-0
[Abstract](103) [FullText HTML](47) [PDF 741KB](16)
As an important land-ocean interaction process, submarine groundwater discharge (SGD) is composed of multiple dynamical processes at different scales and plays an important role in the study of coastal ocean geochemical budgets. However, most of the existing studies focus on the quantification of the total groundwater discharge, few studies are about the differentiation and quantification of groundwater discharge processes at different scales (i.e., short-scale SGD and long-scale SGD). As a world-class river, the Huanghe River is highly turbid and heavily regulated by humans. These natural and anthropogenic factors have a significant impact on groundwater discharge processes in the Huanghe River Estuary (HRE). In this study, the distribution patterns of the natural geochemical tracer radium isotopes (224Ra and 223Ra) and other hydrological parameters in the HRE were investigated during four cruises. By solving the mass balance of 224Ra and 223Ra in the HRE, the long-scale SGD flux was quantified as 0.01−0.19 m/d, and the short-scale SGD flux was 0.03−0.04 m/d. The rate of short-scale SGD remained essentially constant among seasons, while the rate of long-scale SGD varied considerably at different periods and showed a synchronous trend with the variation of river discharge. The results of this study are significant for understanding the SGD dynamics in the HRE and the contribution of SGD to the ocean geochemical budgets.
Simulation of transport mechanism of radium isotopes in aquifer on the southern coast of Laizhou Bay
Yancheng Wang, Guangquan Chen, Hongjun Yu, Xingyong Xu, Yinqiao Zou, Wenqing Zhao, Weitao Han, Wenzhe Lyu, Zhen Cui, Runtian Ding
2023, 42(8): 40-48.   doi: 10.1007/s13131-022-2096-z
[Abstract](270) [FullText HTML](119) [PDF 1175KB](22)
Naturally occurring radium (223Ra, 224Ra, 226Ra, and 228Ra) isotopes have been widely applied as geochemical tracers in marine environments, especially when estimating the submarine groundwater discharge (SGD). In this sense, the influencing factors and transport mechanism of radium isotope activity in aquifers can be key information for SGD estimation. This work evaluates the adsorption/desorption behavior of 224Ra and 226Ra in the solid-liquid phase through a leaching experiment and analysis of field data. The results suggested that radium isotope activity was positively correlated with salinity and grain size, in the case of abundant sediments. Through ion analysis, we found that the ions (Na+, Ca2+, Mg2+, and Ba2+) exchanged with radium isotopes in the process of transport. A 1-D reactive transport model was established to simulate the transport process of radium isotope in aquifers. The model successfully simulated the variation of radium isotope desorption activity with salinity and was subsequently verified in the field. This study contributes to the understanding of the geochemical behavior of radium isotopes in aquifers and provides guidance for selecting a suitable groundwater endmember in SGD estimation.
Combined effect of subsurface dam and layered heterogeneity on groundwater flow and salinity distribution in stratified coastal aquifers
Chao Gao, Jun Kong, Jun Wang, Tong Zhou, Yuncheng Wen
2023, 42(8): 49-60.   doi: 10.1007/s13131-023-2255-x
[Abstract](42) [FullText HTML](16) [PDF 1636KB](4)
In this paper, for the first time, we investigated the combined effect of subsurface dams and a typical stratified aquifer (two high-permeability layers with a low-permeability layer between them) on groundwater flow and salinity distribution in a tidally influenced coastal unconfined aquifer. Subsurface dams can inhibit the invasion of saltwater, and the low-permeability layer (LPL) and tide action can increase the effect of subsurface dams and the removal rate of residual saltwater. Through sensitivity analysis, it was discovered that shifting the dam location towards the inland resulted in a reduction in the effective heights of the dam. The upper saline plume contracted with increasing dam height, and the upper boundary of LPL was moved to shallower regions. And the natural removal time increased significantly with increasing dam height and the bottom boundary of LPL was moved to deeper regions. In addition, if the dam location was close to the sea boundary and the bottom boundary of LPL was moved to deeper regions, we could increase the subsurface dam height to reduce the risks of control of saltwater intrusion. This study provides us a comprehensive understanding of the complex hydrodynamics of saltwater intrusion and provides guides for the design of subsurface dams aimed at saltwater intrusion control in stratified coastal aquifers.
The fate of carbon resulting from pore water exchange in a mangrove and Spartina alterniflora ecozone
Weizhen Jiang, Guizhi Wang, Qing Li, Manab Kumar Dutta, Shilei Jin, Guiyuan Dai, Yi Xu
2023, 42(8): 61-76.   doi: 10.1007/s13131-023-2234-2
[Abstract](160) [FullText HTML](71) [PDF 1585KB](22)
Mangrove and salt-marsh wetlands are important coastal carbon sinks. In order to quantify carbon export via pore water exchange and to evaluate subsequent fate of the exported carbon, we carried out continuous observations in a mangrove-Spartina alterniflora ecozone in the Zhangjiang River Estuary, China. The carbon fluxes via pore water exchange were estimated using 222Rn and 228Ra as tracers to be (2.15 ± 0.63) mol/(m2∙d) for dissolved inorganic carbon (DIC) and (–0.008 ± 0.07) mol/(m2∙d) for dissolved organic carbon (DOC) in the wet season and (3.02 ± 0.65) mol/(m2∙d) for DIC and (–0.15 ± 0.007) mol/(m2∙d) for DOC in the dry season in the mangrove-dominated creek (M-creek), while (2.52 ± 0.82) mol/(m2∙d) for DIC and (0.02 ± 0.09) mol/(m2∙d) for DOC in the dry season in the S. alterniflora-dominated creek (SA-creek). The negative value means that pore water was a sink of DOC in the creek. The total carbon via pore water exchange in the tidal creeks in the mangroves accounted for 41%–55% of the net carbon fixed by mangrove vegetation and was 3–4 times as much as the soil carbon accretion in the mangroves. The exported carbon in the form of DIC contributed all of the carbon outwelling from the M-creek and 79% of the carbon outwelling from the SA-creek, implying effective fixation of carbon by the wetland ecosystem. Moreover, it resulted in 54% in the dry season, 75% in the wet season of the carbon dioxide released from the M-creek to the atmosphere, and 84% of the release from the SA-creek. Therefore, quantification of pore water exchange and related soil carbon loss is essential to trace the fate of carbon fixed in intertidal wetlands.
Spatial distribution and export of nutrients and metal elements in the subterranean estuary of Daya Bay
Zhaoxi Liu, Mingchen Ge, Qianqian Wang, Xuejing Wang, Kai Xiao, Gang Li, Hailong Li
2023, 42(8): 77-86.   doi: 10.1007/s13131-023-2212-8
[Abstract](156) [FullText HTML](64) [PDF 2709KB](31)
Subterranean estuaries (STE) are important seawater-groundwater mixing zones with complex biogeochemical processes, which play a vital role in the migration and transformation of dissolved materials. In this study, we first investigated the spatial distributions of dissolved inorganic nitrogen (DIN), dissolved inorganic phosphorous (DIP), dissolved inorganic silicon (DSi) and metal elements (As, Ba, Cr, Cu, Fe, Mn, Ni, Pb, and Zn) in STE including upper intertidal, seepage face and subtidal zones. We then estimated submarine groundwater discharge (SGD) and associated nutrient and metal element fluxes. From the generalized Darcy’s law method, SGD was estimated to be 30.13 cm/d, which was about 7 times larger than the inflow (4.16 cm/d). The nutrient and metal fluxes from SGD were estimated to be (5.33 ± 4.99) mmol/(m2·d) for DIN, (0.22 ± 0.03) mmol/(m2·d) for DIP, (16.20 ± 2.05) mmol/(m2·d) for DSi, (1325.06 ± 99.10) μmol/(m2·d) for Fe, (143.41 ± 25.13) μmol/(m2·d) for Mn, (304.06 ± 81.07) μmol/(m2·d) for Zn, (140.21 ± 13.33) μmol/(m2·d) for Cu, (84.49 ± 2.94) μmol/(m2·d) for Pb, (37.38 ± 5.51) μmol/(m2·d) for Ba, (27.88 ± 3.89) μmol/(m2·d) for Cr, (10.10 ± 6.33) μmol/(m2·d) for Ni, and (6.25 ± 3.45) μmol/(m2·d) for As. The nutrient and metal fluxes from SGD were relatively higher than those from the inflow, suggesting that nearshore groundwater acted as the sources of nutrients and metal elements discharging into the sea. The environmental potential pollution of coastal seawater was evaluated by pollution factor index (Pi), comprehensive water quality index (CWQI), and ecological risk index (ERI). Pb mainly caused potential danger of nearshore environment with considerable contamination (Pi = 5.78 ± 0.19), heavy pollution (CWQI = 4.09) and high ecological risk (ERI = 18.00). This study contributed to better understanding the behavior of nutrients and metal elements and improving the sustainable management of STE under the pressure of anthropogenic activities and climate change.
Tracing surface seawater mixing and nutrient transport by 222Rn on the northern coast of Beibu Gulf, China
Hao Wang, Qiangqiang Zhong, Fule Zhang, Suiyuan Chen, Hongyan Bao, Jing Lin, Dekun Huang, Tao Yu
2023, 42(8): 87-98.   doi: 10.1007/s13131-023-2233-3
[Abstract](63) [FullText HTML](28) [PDF 1725KB](8)
The transport and diffusion of substances in seawater are limited by the mixing motion of water bodies, while the main forms of mixing in offshore water bodies are advection and eddy diffusion. The eddy diffusion process of water indicates the possible transport direction of dissolved substances. However, the complex environment in the coastal zone makes it difficult to quantitatively assess the water diffusion process. 222Rn is a useful tool to trace the diffusion process of water bodies. However, studies on the 222Rn distribution and its behavior in the Beibu Gulf are scarce. In this study, the activity distribution characteristics of 222Rn in surface seawater of the Guangxi shelf area of the Beibu Gulf were measured. Based on the one-dimensional, steady-state model, the vorticity diffusion coefficient of 222Rn in the horizontal direction was calculated as (0.42−2.13) × 108 m2/d, and the offshore fluxes of 222Rn under the influence of water mixing were calculated as 2.00 × 1012 Bq/d. Correspondingly, the horizontal transport fluxes of silicate, phosphate, nitrite and nitrate were 6.28 × 10−3 mol/(m2·d), 0.10 × 10−3 mol/(m2·d), 0.20 × 10−3 mol/(m2·d) and 4.15 × 10−3 mol/(m2·d), respectively. These results indicate that the study of eddy current diffusion in offshore marine water facilitates a deeper understanding of the water mixing process and nutrient transport and migration.
Phosphorus speciation, transformation and benthic processes with implications for environmental impacts in the aquaculture area of Rushan Bay
Yao Feng, Jun Liu, Aijun Zhang, Yibin Wang, Lu Wang, Zongqing Lv, Xiangbin Ran
2023, 42(8): 99-112.   doi: 10.1007/s13131-023-2235-1
[Abstract](59) [FullText HTML](23) [PDF 1055KB](3)
Phosphorus (P) is an essential nutrient for many organisms in the ocean, which plays a central role in the stability of ecosystems and the evolution of the environment. The distribution, occurrence and source-sink process of P in offshore waters are highly influenced by mariculture activities. P transformation in water-sediment system is the key process in P cycling, however, the mechanism is poorly documented in the coastal sea which is influenced by human activities. Based on the comprehensive surveys in the adjacent waters outside Rushan Bay in May, July and August 2014 and February 2015, the form and transformation of P in the suspended particulate matter (SPM) and surface sediment were analyzed. The results showed that contents of total P, authigenic P and organic P of SPM increased with the increase in distance from the shoreline off Rushan Bay, and the detrital-P decreased. The partition coefficient of P between water and SPM was related to the chemical activity of different forms of P, and a higher reactivity of inorganic P associated with SPM was observed. Hypoxia induced by mariculture changes the distribution and morphological composition of P in SPM and sediment in this typical aquaculture area, which can result in a conversion of sink to source of P in the sediment, thereby having a significant impact on the regional nutrient budget and associated with eutrophication.
Seasonal metal fluxes derived by the interaction of surface water and groundwater in an aquaculture estuary
Xiaoxiong Wang, Jordi Garcia-Orellana, Xiaogang Chen, Jianan Liu, Fenfen Zhang, Jianguo Qu, Zhuoyi Zhu, Jinzhou Du
2023, 42(8): 113-124.   doi: 10.1007/s13131-023-2232-4
[Abstract](89) [FullText HTML](40) [PDF 1039KB](8)
Submarine groundwater discharge (SGD) plays a major role as a conveyor of metals to coastal waters. However, the seasonal change of metal fluxes derived through SGD is unclear. Here, we evaluated the behaviours and fluxes of trace metals (Mn, Fe, Ba, Pb, U, Cr, Zn, Cu) in an estuary under different seasonal conditions. The behaviours of trace metals revealed that SGD was the source of Mn (3.51 mmol/(m2·d)), Fe (0.174 mmol/(m2·d)) and Ba (0.024 mmol/(m2·d)), but the Cu sink (−0.55 μmol/(m2·d)) and other metals exhibited a seasonal source‒sink conversion. The seasonal variation of dissolved organic matter and the fresh groundwater proportion in subterranean estuaries may have an important effect on metals fluxes especially for the Fe, Mn and Ba. Our result shows that the single seasonal metal fluxes estimation applied to the annual scale will cause a large deviation, up to 3.6 times for Fe, 5.5 times for Mn, and 15 times for Ba. Therefore, the influence of seasonal fluctuations on SGD-derived metal fluxes cannot be ignored, and our findings will be important for comprehending the metal budget and cycle in nearshore environment.
Submarine groundwater discharge and seasonal hypoxia off the Changjiang River Estuary
Tianyi Zhu, Bochao Xu, Xiaoyi Guo, Qinsheng Wei, Ergang Lian, Pengxia Liu, William C. Burnett, Qingzhen Yao, Zhigang Yu
2023, 42(8): 125-133.   doi: 10.1007/s13131-023-2256-9
[Abstract](177) [FullText HTML](81) [PDF 1056KB](12)
Hypoxia is a common phenomenon in the sea adjacent to the Changjiang River Estuary (CJE), one of the global major estuaries. Submarine groundwater discharge (SGD) is a widely recognized pathway for terrestrial materials entering the sea, and has been found to be significant off the CJE. We used a 222Rn mass balance model to estimate the SGD fluxes off the CJE and showed that it is linked to seasonal dissolved oxygen (DO) variations. Average SGD fluxes were estimated to be (0.012 ± 0.010) m3/(m2·d) in winter, (0.034 ± 0.015) m3/(m2·d) in summer, and (0.020 ± 0.010) m3/(m2·d) in autumn. We found a significant negative correlation between DO concentrations and SGD rates with groundwater discharge being highest in the summer flood season. In addition, distribution patterns of SGD and hypoxia zones in summer are spatially overlapped, indicating that SGD is an important contributor to summer hypoxia in this region.
Features and factors of radium isotopes in Tianjin’s typical estuaries
Zhe Zhang, Yingchun Dong, Lixin Yi, Xin Hao, Yajie Zheng, Tianxue Lü
2023, 42(8): 134-146.   doi: 10.1007/s13131-023-2146-1
[Abstract](264) [FullText HTML](105) [PDF 1474KB](25)
In order to characterize the features of radium isotopes in estuaries of Tianjin, a continuous survey and sampling of typical estuaries were conducted from 2013 to 2017 in this study. The activities of natural radioactive radium isotopes (223Ra, 224Ra, and 228Ra) in groundwater and surface water were measured by the radium-delayed coincidence counting (RaDeCC) system. The non-conservative behavior of the radium isotopes was investigated under hydrogeochemical conditions and urbanization. The results indicated that in terms of horizontal distribution, the activities of radium in groundwater (Hangu, Tanggu, and Dagang) showed an upward trend from north to south and demonstrated a higher figure than surface water (Haihe River and Duliujian River). Concerning the vertical distribution, the activitives of radium at a 15 m burial depth was higher than that at a 30 m burial depth in all measurements. The activities of radium isotopes in the study area increased with the increase of total dissolved solids, and their desorption behavior on Fe-Mn oxides was constrained by the redox intensity. Different hydrogeological conditions resulted in variations in the vertical profile of radium activities. The activity of radium was regulated by seasonal variation and precipitation in groundwater and surface water. In addition, the rapid urbanization has caused a significant impact on the features of radium isotopes in typical estuaries of Tianjin. Meanwhile, radium isotopes can be applied to reflect the impact of urbanization on surface water-groundwater systems. Clarifying and cleverly utilizing the relationship between behavior of radium isotopes and urbanization will promote the development of the Tianjin Binhai New Area in a healthy way.
Microbiota of a seepage face at the mouth of a subterranean estuary: diversity, distribution and substrate dependence
Yueming Wu, Yongjun Wei, Juan Severino Pino Ibánhez, Danqing Sun, Kaiqi Lu, Qianqian Wang, Jian Li, Shan Jiang
2023, 42(8): 147-157.   doi: 10.1007/s13131-023-2257-8
[Abstract](10) [FullText HTML](4) [PDF 11622KB](3)
Subterranean estuaries, i.e., the mixing zone between terrestrial groundwater and recirculated seawater, host a wide range of microbiota. Here, field campaigns were conducted at the mouth of the subterranean estuary at the Sanggou Bay (Shandong Province, China) over four consecutive seasons at a seepage face (0−20 cm depth). The diversity of benthic microbiome was characterized via 16S rRNA gene sequencing and metagenomics, combined with physic-chemical parameters, e.g., organic carbon, total nitrogen and sulfate contents in sediments. During spring, the dominant species were assigned to the phylum Proteobacteria. Important opportunistic species was assigned to Acidobacteria, Actinobacteria and Bacteroidetes. The key components were identified to be species of the genera Pseudoalteromonas, Colwellia and Sphingobium, indicating the involvement of sediment microbiota in the degradation of sedimentary organic carbon, particularly that of pelagic origin, e.g., phytoplankton detritus and bivalve pseudo-feces. During spring, the microbial community was statistically similar along the depth profiles and among the three sampled stations. Similar spatial distributions were obtained in the remaining seasons. By contrast, the dominant species assemblages varied significantly among seasons, with key genera being Thioprofundum and Nitrosopumilus during summer and autumn and Thioprofundum and Ilumatobacter during winter. Network analysis revealed a seasonal shift in benthic nitrogen and sulfur metabolism associated with these variations in microbial community composition. Overall, our findings suggested that macro elements derived from pelagic inputs, particularly detrital phytoplankton, shaped the microbial community compositions at the seepage face, resulting in significant seasonal variations, while the influence of terrestrial materials transported by groundwater on the sediment microbiota at the seepage face found to be minor.
Linking bacterial and archaeal community dynamics to related hydrological, geochemical and environmental characteristics between surface water and groundwater in a karstic estuary
Xiaogang Chen, Qi Ye, Jinzhou Du, Neven Cukrov, Nuša Cukrov, Yan Zhang, Ling Li, Jing Zhang
2023, 42(8): 158-170.   doi: 10.1007/s13131-023-2185-7
[Abstract](147) [FullText HTML](69) [PDF 2052KB](17)
Subterranean estuaries (STEs) are characterized by the mixing of terrestrial fresh groundwater and seawater in coastal aquifers. Although microorganisms are important components of coastal groundwater ecosystems and play critical roles in biogeochemical transformations in STEs, limited information is available about how their community dynamics interact with hydrological, geochemical and environmental characteristics in STEs. Here, we studied bacterial and archaeal diversities and distributions with 16S rRNA-based Illumina MiSeq sequencing technology between surface water and groundwater in a karstic STE. Principal-coordinate analysis found that the bacterial and archaeal communities in the areas where algal blooms occurred were significantly separated from those in other stations without algal bloom occurrence. Canonical correspondence analysis showed that nutrients and salinity can explain the patterns of bacterial and archaeal community dynamics. The results suggest that hydrological, geochemical and environmental characteristics between surface water and groundwater likely control the bacterial and archaeal diversities and distributions in STEs. Furthermore, we found that some key species can utilize terrestrial pollutants such as nitrate and ammonia in STEs, indicating that these species (e.g., Nitrosopumilus maritimus, Limnohabitans parvus and Simplicispira limi) may be excellent candidates for in situ degradation/remediation of coastal groundwater contaminations concerned with the nitrate and ammonia. Overall, this study reveals the coupling relationship between the microbial communities and hydrochemical environments in STEs, and provides a perspective of in situ degradation/remediation for coastal groundwater quality management.
Optimization of enrichment and pretreatment of low-activity radium isotopes in the open ocean
Guiyuan Dai, Guizhi Wang, Qing Li, Weizhen Jiang, Fei Zhang
2023, 42(8): 171-177.   doi: 10.1007/s13131-023-2152-3
[Abstract](111) [FullText HTML](45) [PDF 602KB](11)
In the open ocean, radium isotopes are useful tracers of residence time and water-mass mixing. However, limited by the measurement resolution of commonly used gamma counters, the low activity of radium in the open ocean makes it necessary to enrich radium from large volumes of seawater and pretreat radium-enriched carriers prior to measurements. The commonly applied method of radium enrichment and pretreatment, however, has limitations of uneven coating of MnO2 on cartridges, relatively expensive cartridges, time-consuming issues during cartridge-ashing, ash loss during transfer, and changes of gamma counters efficiency caused by different ash weights. To address these issues, in this study we optimized the enrichment and pretreatment of low-activity radium prior to measurements. Firstly, we replaced commonly used acrylic cartridges with cheaper polypropylene cartridges, which took 6 h to be ashed, 42 h shorter than for acrylic cartridges. Secondly, MnO2-coated cartridges were prepared with a circulating hot acidic KMnO4 solution to ensure homogeneous coating. The radium extraction efficiency of this MnO2-coated cartridge was 20%–61% higher than that prepared by directly immersing cartridges in the solution. The radium delayed coincidence counter efficiency for MnO2-coated cartridge was stable with a moisture content of 0.05–1. Lastly, after ashing cartridges, instead of directly transferring the ash to a measurement vial, a mixture of hydroxylamine hydrochloride and hydrochloric acid was used to completely leach the ash for long-lived radium, followed by coprecipitation by BaSO4, to avoid potential loss of ash during transfer and variations in measurement geometry due to different ash weights. And the recovery of long-lived radium pretreatment was 94%–102%, which improved by 11% compared with the common method. In addition, the radium extraction efficiency of the MnO2-coated cartridge varied from 3% to 4% within the in situ pump working flow rate of 4–7 L/min, which fell within the measurement errors.
In-situ detection equipment for radon-in-water: unattended operation and monthly investigations
Chunqian Li, Meng Li, Guangquan Chen, Huaming Yu, Chenglun Zhang, Wen Liu, Jinjia Guo, Shibin Zhao, Lijun Song, Xiliang Cui, Ying Chai, Lu Cao, Diansheng Ji, Bochao Xu
2023, 42(8): 178-184.   doi: 10.1007/s13131-023-2238-y
[Abstract](72) [FullText HTML](29) [PDF 2447KB](7)
Radon is recognized as a powerful tracer of certain geophysical processes in marine and aquatic environments. In the past few decades, the instruments and methods for measuring radon concentration in water have been developed to some extent but still lack underwater in-situ measurements. Here we present an in-situ detection equipment for radon-in-water (pulsed ionization chamber (PIC)-radon) to measure dissolved radon in ocean and groundwater settings. The equipment has been successfully deployed in the Jiaozhou Bay in July 2022 and has achieved 14 d of unattended underwater in-situ observation. Then it was successfully placed in a groundwater monitoring well in the Laizhou Bay in November 2022 and monitored radon activities for over 30 d. The results showed that this instrument had a good indication of submarine groundwater discharge. The PIC-radon detector takes advantage of smaller size, lower power consumption, and is barely influenced by humidity, making it particularly suitable for long-term in-situ measurement, especially in harsh environments with limited human care or deployment spaces.
Measuring 222Rn in aquatic environment via Pulsed Ionization Chamber Radon Detector
Lijun Song, Wen Liu, Shibin Zhao, Chunqian Li, Jinjia Guo, Natasha Dimova, Bochao Xu
2023, 42(8): 185-189.   doi: 10.1007/s13131-023-2183-9
[Abstract](236) [FullText HTML](95) [PDF 1561KB](13)
Radon (Rn) is a naturally occurring radioactive inert gas in nature, and 222Rn has been routinely used as a powerful tracer in various aquatic environmental research on timescales of hours to days, such as submarine groundwater discharge. Here we developed a new approach to measure 222Rn in discrete water samples with a wide range of 222Rn concentrations using a Pulsed Ionization Chamber (PIC) Radon Detector. The sensitivity of the new PIC system is evaluated at 6.06 counts per minute for 1 Bq/L when a 500 mL water sample volume is used. A robust logarithmic correlation between sample volumes, ranging from 250 mL to 5000 mL, and system sensitivity obtained in this study strongly suggests that this approach is suitable for measuring radon concentration levels in various natural waters. Compared to the currently available methods for measuring radon in grab samples, the PIC system is cheaper, easier to operate and does not require extra accessories (e.g., drying tubes etc.) to maintain stable measurements throughout the counting procedure.

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