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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](0) [FullText HTML](0)
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.
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
 doi: 10.1007/s13131-023-2211-9
[Abstract](7) [FullText HTML](3) [PDF 2547KB](0)
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.
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
 doi: 10.1007/s13131-023-2255-x
[Abstract](14) [FullText HTML](6)
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 (USP) contracted with increasing dam height, and the upper boundary of LPL was moved to shallower regions. And the natural removal time (tr) 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.
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
 doi: 10.1007/s13131-023-2256-9
[Abstract](23) [FullText HTML](10)
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.
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](6) [FullText HTML](2)
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.
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](77) [FullText HTML](38)
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.
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
 doi: 10.1007/s13131-023-2182-x
[Abstract](93) [FullText HTML](39) [PDF 1145KB](9)
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.
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
 doi: 10.1007/s13131-023-2233-3
[Abstract](29) [FullText HTML](13) [PDF 1799KB](4)
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.
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
 doi: 10.1007/s13131-023-2236-0
[Abstract](46) [FullText HTML](20) [PDF 824KB](4)
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.
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
 doi: 10.1007/s13131-023-2238-y
[Abstract](34) [FullText HTML](13) [PDF 1884KB](4)
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.
The influence of bioturbation on sandy reservoirs: the delta front sand of the lower Zhujiang Formation, Baiyun Sag, Zhujiang River Mouth Basin
Zhifeng Xing, Wei Wu, Juncheng Liu, Yongan Qi, Wei Zheng
 doi: 10.1007/s13131-022-2116-z
[Abstract](13) [FullText HTML](5)
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.
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](11) [FullText HTML](5)
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](12) [FullText HTML](4)
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.
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
 doi: 10.1007/s13131-023-2232-4
[Abstract](32) [FullText HTML](13)
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.
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
 doi: 10.1007/s13131-023-2234-2
[Abstract](63) [FullText HTML](26) [PDF 1115KB](12)
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.
Multi-proxy reconstructions of hydrological changes from continental shelf sediments in the northern South China Sea during the interval 9 200–6 200 cal yr BP
Chao Huang, Xiaoxu Qu, Lihui Wang, Yuhan Xie, YongYi Luo, Fajin Chen, Yin Yang
 doi: 10.1007/s13131-023-2155-0
[Abstract](44) [FullText HTML](15)
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 from 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 yr BP, followed by a cold and dry climate from 7 600 cal yr BP to 6 500 cal yr BP, and progressive humidification during the period 6 500–6 200 cal yr BP. A prominent hydrological anomaly occurred during 7 600–6 500 cal yr 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.
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
 doi: 10.1007/s13131-023-2235-1
[Abstract](36) [FullText HTML](14)
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.
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](153) [FullText HTML](58)
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.
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
 doi: 10.1007/s13131-023-2212-8
[Abstract](128) [FullText HTML](52)
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.
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
 doi: 10.1007/s13131-023-2183-9
[Abstract](185) [FullText HTML](70) [PDF 1119KB](11)
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.
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](25) [FullText HTML](9)
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](192) [FullText HTML](87)
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](96) [FullText HTML](30)
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](121) [FullText HTML](49)
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](68) [FullText HTML](25)
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](67) [FullText HTML](25)
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](117) [FullText HTML](42)
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.
The effect of Typhoon Kalmaegi on the modal energy and period of internal waves near the Dongsha Islands (South China Sea)
Rong-Wei Zhai, Gui-Ying Chen, Chenjing Shang, Xiao-Dong Shang, Youren Zheng
 doi: 10.1007/s13131-023-2206-6
[Abstract](83) [FullText HTML](34)
The influence of typhoon Kalmaegi on internal waves near the Dongsha Islands in the northeastern South China Sea was investigated using mooring observation data. We observed, for the first time, that the phenomenon of regular variation characteristics of the 14-d spring-neap cycle of diurnal internal tides (ITs) can be regulated by typhoons. The diurnal ITs lost the regular variation characteristics of the 14-d spring-neap cycle during the typhoon period owing to the weakening of diurnal coherent ITs, represented by \begin{document}$ {O}_{1} $\end{document} and \begin{document}$ {K}_{1} $\end{document}, and the strengthening of diurnal incoherent ITs. Results of quantitative analysis showed that during the pre-typhoon period, time-averaged modal kinetic energy (sum of modes 1–5) of near-inertial internal waves (NIWs) and diurnal and semidiurnal ITs were 0.62, 5.66, and 1.48 \begin{document}$ \mathrm{k}\mathrm{J}/{\mathrm{m}}^{2} $\end{document}, respectively. However, during the typhoon period, the modal kinetic energy of NIWs increased 5.11 times, mainly due to the increase in high-mode kinetic energy. At the same time, the modal kinetic energy of diurnal and semidiurnal ITs was reduced by 68.9 % and 20 %, respectively, mainly due to the decrease in low-mode kinetic energy. The significantly reduced diurnal ITs during the typhoon period could be due to: (1) strong nonlinear interaction between diurnal ITs and NIWs, and (2) a higher proportion of high-mode diurnal ITs during the typhoon period, leading to more energy dissipation.
Modeling wave attenuation by vegetation with accompanying currents in SWAN
Hong Wang, Zhan Hu
 doi: 10.1007/s13131-023-2199-1
[Abstract](75) [FullText HTML](32)
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](95) [FullText HTML](33)
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.
Technical development of operational in-situ marine monitoring and research on its key generic technologies in China
Yunzhou Li, Juncheng Wang
[Abstract](26) [FullText HTML](8)
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 C-MAN station, ocean data buoy and VOS measuring 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.
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
 doi: 10.1007/s13131-022-2096-z
[Abstract](233) [FullText HTML](103)
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.
Features and factors of radium isotopes in Tianjin’s typical estuaries
Zhe Zhang, Yingchun Dong, Lixin Yi, Xin Hao, Yajie Zheng, Tianxue Lü
 doi: 10.1007/s13131-023-2146-1
[Abstract](234) [FullText HTML](94)
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 activity of natural radioactive radium isotopes (223Ra, 224Ra, and 228Ra) in groundwater and surface water was measured by the radium-delayed coincidence counting (RaDeCC) system. The non-conservative behavior of the radium isotope was investigated under hydrogeochemical conditions and urbanization. The results indicated that in terms of horizontal distribution, the activity 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 and Duliujianhe). Concerning the vertical distribution, the activity of radium at a 15 m burial depth was higher than that at a 30 m burial depth in all measurements. The activity 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 activity. 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.
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
[Abstract](107) [FullText HTML](50)
Subterranean estuaries (STEs) are characterized by the mixing of terrestrial fresh groundwater and seawater in a coastal aquifer. 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.
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](113) [FullText HTML](39)
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](110) [FullText HTML](25)
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.
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 ZHANF, Jing WANG
 doi: 10.1007/s13131-023-2186-6
[Abstract](163) [FullText HTML](64)
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.
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](303) [FullText HTML](120)
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.
Optimization of enrichment and pretreatment of low-activity radium isotopes in the open ocean
Guiyuan Dai, Guizhi Wang, Qing Li, Weizhen Jiang, Fei Zhang
[Abstract](97) [FullText HTML](40)
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%–4% within the in situ pump working flow rate of 4–7 L/min, which fell within the measurement errors.
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](182) [FullText HTML](40)
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](139) [FullText HTML](42)
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](253) [FullText HTML](86)
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](579) [FullText HTML](165)
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.
2023, 42(7).  
[Abstract](24) [PDF 8874KB](11)
2023, 42(7).  
[Abstract](17) [FullText HTML](6) [PDF 60KB](3)
Beach Protection and Restoration around the South China Sea
Using video imagery to reconstruct the 3D intertidal terrain along a beach with multiple cusps
Feng Cai, Hang Yin, Hongshuai Qi, Jixiang Zheng, Yuwu Jiang, Zhubin Cao, Yanyu He
2023, 42(7): 1-9.   doi: 10.1007/s13131-023-2174-x
[Abstract](205) [FullText HTML](93) [PDF 7306KB](22)
A high-frequency, high-resolution shore-based video monitoring system (VMS) was installed on a macrotidal (tidal amplitude >4 m) beach with multiple cusps along the Quanzhou coast, China. Herein, we propose a video imagery-based method that is coupled with waterline and water level observations to reconstruct the terrain of the intertidal zone over one tidal cycle. Furthermore, the beach cusp system (BCS) was precisely processed and embedded into the digital elevation model (DEM) to more effectively express the microrelief and detailed characteristics of the intertidal zone. During a field experiment conducted in January 2022, the reconstructed DEM was deemed satisfactory. The DEM was verified by RTK-GPS and had an average vertical root mean square error along corresponding RTK-GPS-derived intertidal profiles and corresponding BCS points of 0.134 m and 0.065 m, respectively. The results suggest that VMSs are an effective tool for investigating coastal geomorphic processes.
Sediment source-to-sink process variations of sandy-muddy transitional beaches and their morphological indications
Shaohua Zhao, Feng Cai, Hongshuai Qi, Jianhui Liu, Chao Cao, Gen Liu, Gang Lei
2023, 42(7): 10-24.   doi: 10.1007/s13131-022-2077-2
[Abstract](283) [FullText HTML](135) [PDF 4237KB](23)
The clay mineralogy of 28 sandy-muddy transitional beach (SMT-Beach) sediments and surrounding mountain river sediments along the coasts of southeastern China was systematically investigated to reveal the sediment source-to-sink process variations of such beaches and their morphological indications. The results show that the clay mineral assemblages of these SMT-Beaches mainly comprise of almost equal illite (~30%), kaolinite (~28%), chlorite (~22%), and smectite (~20%) contents. From the surrounding mountain rivers to the SMT-Beaches, clay mineral assemblages show distinct spatial changes characterized by a large decrease (~40%) in kaolinite, whereas the other three clay minerals present relative increases, especially clear for smectite. The muddy sediment sources of SMT-Beaches inferred from the clay mineralogy are mainly derived from nearby mountain rivers coupled with long-distance transport and penetration of the Changjiang River. The sandy sediments of these beaches are predominantly sourced from nearby mountain rivers, the weathering products of surrounding rocks in both mainland and island environments, and erosion of the “Old Red Sand” and “Red Soil Platform”. However, the sandy sediment sources of the SMT-Beaches are largely reduced because of the remarkable decrease in the river fluvial supply associated with intensive human activities such as dam construction and coastal reclamation. Subsequently, the sandy sections of SMT-Beaches present clear erosion and have revealed by both time series remote sensing images and a compilation of published literature. In contrast, the muddy sediment supply of SMT-Beaches is temporarily stable and relatively constant, resulting in the landward migration of the mudflats with relative transgression or accumulation. These findings highlight that the natural evolution processes of SMT-Beaches have been greatly reshaped by intensive human activities.
Typhoon vs. cold wave: a comparative assessment of geomorphic response and boulder displacement using RFID technology
Lingbo Li, Feng Cai, Hongshuai Qi, Lulu Qiao, Shaohua Zhao, Gen Liu, Jianhui Liu
2023, 42(7): 25-40.   doi: 10.1007/s13131-022-2083-4
[Abstract](86) [FullText HTML](36) [PDF 8190KB](21)
Extreme storm events in coastal zones play significant roles in shaping the morphology of boulder beaches. However, boulder displacement and the geomorphological evolution of boulder beaches driven by different extreme storm events, especially typhoon events, remain poorly understood. Thus, boulder displacement and the geomorphic response on a boulder beach in Fujian, southeastern China, were explored before, during and after a cold wave event (Dec. 1–7, 2020) and before and after Typhoon In-Fa (Jul. 19–27, 2021), a large tropical storm. This was achieved by tracking 42 tagged boulders distributed in the intertidal and supratidal zones using Radio Frequency Identification (RFID) and topographic surveys using real-time kinematic techniques, respectively. The results showed obvious disparities in boulder displacement in different geomorphic zones due to cold wave and typhoon events that were mainly characterized by migration magnitude, range, direction, and mode of transport. The typhoon event led to rapid and substantial changes in the overall morphology of the boulder beach, while the cold wave event impacted the intertidal morphology of the boulder beach to only a small extent. The surrounding structure of boulders, beach slope and beach elevation had a combined dominant effect on boulder displacement under the same extreme event. Hydrodynamic factors (effective wave energy fluxes, incident wave direction, storm surge and water level) had dominant effects on boulder displacement during different extreme events. In terms of a single event, the magnitude of the boulder displacement driven by the typhoon was much greater than that driven by the cold wave. However, considering the frequency and duration of cold waves in winter, the impact of multiple consecutive cold waves on the geomorphology of the boulder beach cannot be ignored in this study area. Alternating and repeated interactions between these two processes constitute the complete geomorphic evolution of the boulder beach. This study contributes to improved predictions of the morphodynamic response of boulder beaches to future storms, especially large tropical storms, and facilitates better coastal management.
An investigation of the morphodynamic change of reef islands under monochromatic waves
Yu Yao, Baobao Zhou, Zhongwei Zhao, Xianjin Chen, Long Chen
2023, 42(7): 41-50.   doi: 10.1007/s13131-023-2156-z
[Abstract](148) [FullText HTML](63) [PDF 1845KB](16)
The persistence and habitability of coral reef islands in future extreme oceanographic conditions has received increasing attention in the recent decade, concerning that the sea level rise (SLR) and more frequent and intense storms in the context of global climate change are expected to destabilize those islands. Here, we conduct a set of wave-flume laboratory experiments focusing on the morphodynamic change of reef islands to varying ocean forcing conditions (wave height and SLR). Subsequently, a phase-resolving XBeach numerical model is adopted to simulate the monochromatic wave process and its associated sediment dynamics. The adopted model is also firstly validated by laboratory experimental results as reported in this study. It is then used to examine the impacts of island morphological factors (island width, island height, island location and island side slope) on the island migration. The combined laboratory/physical and numerical experiment outputs suggest that reef islands can accrete vertically in response to the sea level rise and the increased storminess.
Morphodynamic response of an embayed beach to different typhoon events with varying intensities
Lianqiang Shi, Junli Guo, Shenliang Chen, Yang Chang, Daheng Zhang, Zhaohui Gong
2023, 42(7): 51-63.   doi: 10.1007/s13131-023-2164-z
[Abstract](96) [FullText HTML](40) [PDF 2151KB](9)
Beach erosion has occurred globally in recent decades due to frequent and severe storms. Dongsha beach, located in Zhujiajian Island, Zhejiang Province, China, is a typical embayed sandy beach. This study focused on the morphodynamic response of Dongsha beach to typhoon events, based on beach topographies and surficial sediment characteristics acquired before and after four typhoon events with varying intensities. The four typhoons had different effects on the topography and sediment characteristics of Dongsha beach. Typhoons Ampil and Danas caused the largest (−51.72 m3/m) and the smallest erosion (−8.01 m3/m), respectively. Remarkable alongshore patterns of beach profile volumetric changes were found after the four typhoon events, with more erosion in the southern and central parts of the beach and few changes in the northern part. Grain size coarsening and poor sorting were the main sediment patterns on the beach influenced by different typhoons. Typhoons that occurred in the same year after another typhoon enhanced the effect of the previous typhoon on sediment coarsening and sorting variability, but this cumulative effect was not found between typhoons that occurred during different years. A comparison of the collected data revealed that the topographic state of the beach before the typhoon, typhoon characteristics, and tidal conditions were possible reasons for the difference in the responses of Dongsha beach to typhoon events. More severe beach erosion was caused by typhoons with higher intensity levels and longer durations, and high tide levels during typhoons can determine the upper limit of the beach profile erosion site. Taken together, these results can be used to improve beach management for storm prevention.
Dynamic geomorphology and storm response characteristics of the promontory-straight beach—a case of Gulei Beach, Fujian
Chao Cao, Zijian Mao, Feng Cai, Hongshuai Qi, Jianhui Liu, Gang Lei, Shaohua Zhao, Gen Liu
2023, 42(7): 64-78.   doi: 10.1007/s13131-023-2225-3
[Abstract](104) [FullText HTML](45) [PDF 4442KB](11)
As one of the main areas of tropical storm action in the northwestern Pacific Ocean, South China experiences several typhoons each year, and coastal erosion is a problem, making the area a natural testing ground for studying the dynamic geomorphological processes and storm response of promontory-straight coasts. This study is based on three years of topographic data and remote sensing imagery of Gulei Beach and uses topographic profile morphology, single width erosion-accretion and mean change, combined with the Coastsat model to quantify the seasonal and interannual variability and storm response of the beach and to explain the evolution of shoreline change and beach dynamics geomorphology in the last decade. Gulei Beach has been in a state of overall erosion and local accretion for a long time, with relatively obvious cyclical changes; seasonal changes are also obvious, which are mainly characterized by summer accretion and winter erosion, with accretion at the top of the bay and accretion and erosion on the north and south sides of the bay corner, respectively; the seasonal erosion-accretion volume of the beach profile ranges from −80 m3/m to 95.52 m3/m, and the interannual erosion-accretion volume ranges from −69.09 m3/m to 87.31 m3/m. The response of beaches to typhoons with different paths varies greatly depending on the length, slope, orientation and scale of beach development. The large and gently developing Futou beach is less responsive to storms, while the less developed headlands in the southern Gulei Peninsula are more susceptible to disturbance by external factors and respond more strongly to typhoons. Storm distance is more influential than storm intensity. Under the influence of human activities, obvious erosion hotspots develop during normal weather, but storm processes produce redistribution of beach material patterns, and erosion hotspots disappear after storms. The results of this study enrich the theory of beach dynamics geomorphology and provide technical support for disaster prevention and mitigation, as well as ecological restoration of coastal zones.
Coastal erosion risk assessment of Hainan Island, China
Qianxin Su, Zhiqiang Li, Gaocong Li, Daoheng Zhu, Pengpeng Hu
2023, 42(7): 79-90.   doi: 10.1007/s13131-022-2122-1
[Abstract](120) [FullText HTML](51) [PDF 4589KB](13)
Coastal erosion on islands is increasing due to sea level rise, frequent extreme events, and anthropogenic activities. However, studies on the multifactorial coastal erosion risk and the vulnerability of islands are limited. In this study, the Coastal Erosion Risk Assessment (CERA) method was applied for the first time to the study area in China to assess the erosion risk on the coast of Hainan Island; to explore the effects of coastal ocean dynamics, sediment movement characteristics, and anthropogenic construction; and to discuss the suitability of the method and countermeasures for coastal protection. The results show that the coast of Hainan Island shows high sensitivity, high value, low exposure, and moderate erosion. The whole island showed high vulnerability but low erosion risk, with the eastern region being more affected by erosion, particularly the eastern side of Wulong Port and Yalin Bay in Wenchang, and the shore section of Yalong Bay in Sanya, having a very high risk of coastal erosion. In addition, Monte Carlo simulation was used to check the applicability of the CERA method, and it was found that the rate of shoreline change, population density, and number of storms significantly contributed to coastal erosion, but only the short-term effects of sea level rise were considered. The effects of sea level rise and sediment grain size were primarily analyzed as influencing factors. The effects of sea level rise continue to strengthen, with coastal retreat expected to be greater than 2 m by the mid-21st century. Moreover, Hainan Island is primarily composed of the fine and medium sand types, which have little resistance to coastal erosion. Currently, the impact of sediment grain size is rarely considered in coastal erosion risk assessment studies. However, it can be incorporated into the indicator system in the future, and the spatial variation of indicators can be fully considered to strengthen the refinement study.
Erosion hotspot identified along the sandy coast of Shanwei: characteristics and origin
Jitao Yu, Yuanting Ding, Lin Zhang, Pei Liu, Renfu Fan
2023, 42(7): 91-102.   doi: 10.1007/s13131-022-2124-z
[Abstract](126) [FullText HTML](56) [PDF 3179KB](11)
Based on the measured beach profile data of Sanzhou Bay from 2015 to 2019, an erosion hotspot was identified along the Shanwei coastline of eastern Guangdong, where the maximum retreat distance of the shoreline exceeded 80 m and the erosion rate was more than 20 m/a. To determine the time at which the erosion hotspot started and the potential causes of its formation, this study used 63 Landsat satellite images from 1986 to 2019 to construct a time series of shoreline positions over the past 30 years by extracting their high-tide shorelines. Next, the M-K trend test method was introduced to evaluate the non-linear shoreline behavior based on the single-transect method. The results showed that the time of approximately 2013 marked the start of the erosion hotspot, the erosion hotspot was characterized by erosion rates of more than 2 m/a (a maximum rate of 31.6 m/a), and the affected shoreline more than 4.3 km from 2013 to 2019. Furthermore, this erosion hotspot was proved to be caused by artificial sand mining in the nearshore zone, which destroyed the original beach’s morphodynamic equilibrium. With the aid of storm events, soil cliffs composed of loose sediment on the backshore were sacrificed to achieve a new equilibrium, resulting in an extremely significant retreat parallel to the coast on the west side of the study area, which reflects the combined effect of human and natural processes. This study provides a concrete example of the rapid response of shorelines to artificial sand mining activities, and the associated finding is a stark warning about the cautious development and utilization of coastal zones and the strict regulation of human activities.
Dramatical hydro-sedimentary changes induced by bamboo fences over mangrove tidal flat of the largest delta in Beibu Gulf, southwestern China
Zuming Huang, Zhijun Dai, Riming Wang, Xiaoyan Zhou, Wenhong Pang, Jiejun Luo, Bingbin Feng, Baoqing Hu
2023, 42(7): 103-115.   doi: 10.1007/s13131-022-2117-y
[Abstract](195) [FullText HTML](66) [PDF 2207KB](19)
Mangrove forest is one of the most important ecological and environmental resources by effectively promoting tidal flat deposition and preventing the coastal region from typhoon. However, there have been mass loss of mangrove forests due to anthropogenic activities. It is an urgent need to explore an effective way for mangrove restoration. Here, three rows of bamboo fences with hydro-sedimentary observation set over Aegiceras corniculatum mangrove tidal flat of the Nanliu Delta, the largest delta of Beibu Gulf, China, were conducted to analyze the hydro-sedimentary variations induced by bamboo fences. Results identified that the mean horizontal velocity Um per burst (20 min) decreased by as much as 71% and 40% in comparison with those without bamboo fences in March and November, respectively, when the tidal current entering the bamboo area during flood. The maximum of mean horizontal flow velocity Um-max at bamboo area was 50%–75% of that without bamboo fences during ebb tide. The suspended sediment concentration of bamboo area suggested a maximum reduction of 57% relative to bare flat during flood, and was 80% lower than bare flat at ebb peak. Moreover, the turbulent kinetic dissipation ε at flood tide was significantly higher than that at ebb tide, while the bamboo fences greatly increased the turbulent kinetic dissipation ε by 2 to 5 times relative to bare flat, resulting in an increase of the bed elevation by inhibiting the sediment incipient motion and intercepting suspended sediment. The siltation rate at the bamboo area was 140% and 29.3% higher than that at the bare flat and the region covered with A. corniculatum, respectively. These results highlight that bamboo fences can effectively attenuate tidal current and thus promote siltation over mangrove flat, which contribute great benefit to mangrove survival.
Dramatic changes in the horizontal structure of mangrove forests in the largest delta of the northern Beibu Gulf, China
Riming Wang, Zhijun Dai, Hu Huang, Xixing Liang, Xiaoyan Zhou, Zhenming Ge, Baoqing Hu
2023, 42(7): 116-123.   doi: 10.1007/s13131-022-2126-x
[Abstract](250) [FullText HTML](90) [PDF 1908KB](9)
The horizontal structure of mangrove forests is an important characteristic that reflects a significant signal for coupling between mangroves and external drivers. While the loss and gain of mangroves has received much attention, little information about how the horizontal structure of mangrove forests develops from the seedling stage to maturity has been presented. Here, remote sensing images taken over approximately 15 years, UVA images, nutrient elements, sediments, and Aegiceras corniculatum vegetation parameters of the ecological quadrats along the Nanliu Delta, the largest delta of the northern Beibu Gulf in China, are analyzed to reveal changes in the horizontal structure of mangroves and their associated driving factors. The results show that both discrete structures and agglomerated structures can often be found in A. corniculatum seedlings and saplings. However, the combination of seedlings growing into maturity and new seedlings filling in available gaps causes the discrete structure of A. corniculatum to gradually vanish and the agglomerate structure to become stable. The aggregated structure of seedlings, compared to the discrete structure, can enhance the elevation beneath mangroves by trapping significantly more sediments, providing available spaces and conditions for seedlings to continue growing. Furthermore, by catching fine sediments with enriched nutrients, the survival rate of A. corniculatum seedlings in the agglomerated structure can be much higher than that in the discrete structure. Our results highlight the significance of the agglomeration of A. corniculatum, which can be beneficial to coastal mangrove restoration and management.
Experimental study on the mitigation effect of mangroves during tsunami wave propagation
Cheng Chen, Chen Peng, Hui Yan, Minjian Wei, Tingyu Wang
2023, 42(7): 124-137.   doi: 10.1007/s13131-023-2161-2
[Abstract](72) [FullText HTML](30) [PDF 5801KB](7)
Mangroves are crucial for protecting coastal areas against extreme disasters such as tsunamis and storm surges. An experimental study was conducted to determine how mangroves can mitigate the tsunami wave propagation. The test was performed in a flume, where mangrove models were installed on a slope, and dam-burst waves were used to simulate tsunami waves. To study how mangrove forests reduce the impact of tsunamis, this paper measured the heights of the incoming waves under different initial conditions (tsunami wave intensity and initial water depth) and plant factors (arrangement and distribution density) and described the reduction process. The results show that, after passing through the mangrove, the tsunami bore height will decrease within a certain range as the initial water depth increases. However, there is no correlation between the increase of inundation level and the drop of water level. The bore height attenuation is more significant at higher density of mangroves, but after tsunami passing through the mangroves, the relative bore height will decrease. When the distribution density of mangroves is constant, the wave attenuation at different locations (before, on and after the slope) shows different relationships with the initial water depth and wave height for different models. The transmission coefficient (\begin{document}$ {K }_{i} $\end{document}) shows a parabolic correlation with its density. The proportion of the energy loss caused by the mangrove resistance to the total energy (\begin{document}$ {E }_{b} $\end{document}) is defined as \begin{document}$ {C}_{m2} $\end{document}. The variation trend of \begin{document}$ {C}_{m2} $\end{document} corresponds to the tsunami wave energy attenuation rate (\begin{document}$ {C}_{a} $\end{document}) and \begin{document}$ {K }_{i} $\end{document}.
Nourishment and disaster mitigation efficiency of feeding sand on the dry section of a dissipative beach
Yazhuang Zhao, Hongshuai Qi, Shaohua Zhao, Feng Cai, Jianhui Liu, Pu Xu, Zheyu Xiao, Yanyu He, Zhiyong Zhang
2023, 42(7): 138-148.   doi: 10.1007/s13131-023-2193-7
[Abstract](53) [FullText HTML](18) [PDF 1491KB](6)
To explore the nourishment effect and disaster reduction efficiency of a fully dissipative dry beach under the impact of storms, this paper uses the measured topography and hydrodynamic data to establish a one-dimensional numerical model of the XBeach beach profile. By numerically modeling the change in the nourished profile for different dry beach widths under normal waves and storm conditions and the recovery process of the profile after the storm, the degree of response in dry beach nourishment for the fully dissipative beach is analyzed. The results show that under normal wave conditions, the response of the nourished dry beach is obvious. Sediment on the dry beach erodes heavily, and the shoreline moves landward over a long distance. With the increase in the width and size of the dry beach, the wave height at the bottom of the backshore profile decreases, the wave height attenuation rate increases continuously, and the wave elimination effect is remarkable. When the storm incident wave intensifies, the wave height attenuation rate of the nourished dry beach decreases, indicating that the smaller the storm intensity is, the more significant the wave reduction effect of the nourished dry beach is. At the same time, different profile arrangements of nourished dry beaches suffer from different degrees of erosion under storm conditions, with significant changes in profile morphology. With intensified storm action, the intensity of sediment erosion in the nourished dry beach increases, the nourishment is weakened, and the recovery effect of the profile after the storm is not obvious. The results of the numerical modeling highlight that the dry beach nourishment method can resist storms to a certain extent, but the overall effect is relatively limited.
Variation in cross-shore wind speeds influenced by the morphology of nourished beach
Xu Chen, Jianhui Liu, Feng Cai, Yanyu He, Bailiang Li, Hongshuai Qi, Shaohua Zhao, Gen Liu
2023, 42(7): 149-159.   doi: 10.1007/s13131-023-2224-4
[Abstract](107) [FullText HTML](48) [PDF 1379KB](8)
The cross-shore variation in wind speeds influenced by beach nourishment, especially the dramatic changes at the nourished berm, is important for understanding the aeolian sand transport processes that occur after beach nourishment, which will contribute to better beach nourishment project design on windy coasts. In this paper, the influencing factors and potential mechanism of wind speed variation at the edge of a nourished berm were studied. Field observations, together with the Duna model, were used to study the cross-shore wind speed distribution for different nourishment schemes. The results show that the nourished berm elevation and beachface slope are the main factors controlling the increase in wind speed at the berm edge. When the upper beach slope is constant, the wind speed at the berm edge has a positive linear correlation with the berm elevation. When the berm elevation remains constant, the wind speed at the berm edge is also proportional to the upper beach slope. Considering the coupling effects of nourished berm elevation and beachface slope, a model for predicting the wind speed amplification rate at the nourished berm edge was established, and the underlying coupling mechanism was illustrated.
Vulnerability assessment of coastal wetlands in Minjiang River Estuary based on cloud model under sea level rise
Xiaohe Lai, Chuqing Zeng, Yan Su, Shaoxiang Huang, Jianping Jia, Cheng Chen, Jun Jiang
2023, 42(7): 160-174.   doi: 10.1007/s13131-023-2169-7
[Abstract](194) [FullText HTML](88) [PDF 3691KB](13)
The change of coastal wetland vulnerability affects the ecological environment and the economic development of the estuary area. In the past, most of the assessment studies on the vulnerability of coastal ecosystems stayed in static qualitative research, lacking predictability, and the qualitative and quantitative relationship was not objective enough. In this study, the “Source-Pathway-Receptor-Consequence” model and the Intergovernmental Panel on Climate Change vulnerability definition were used to analyze the main impact of sea level rise caused by climate change on coastal wetland ecosystem in Minjiang River Estuary. The results show that: (1) With the increase of time and carbon emission, the area of high vulnerability and the higher vulnerability increased continuously, and the area of low vulnerability and the lower vulnerability decreased. (2) The eastern and northeastern part of the Culu Island in the Minjiang River Estuary of Fujian Province and the eastern coastal wetland of Meihua Town in Changle District are areas with high vulnerability risk. The area of high vulnerability area of coastal wetland under high emission scenario is wider than that under low emission scenario. (3) Under different sea level rise scenarios, elevation has the greatest impact on the vulnerability of coastal wetlands, and slope has less impact. The impact of sea level rise caused by climate change on the coastal wetland ecosystem in the Minjiang River Estuary is mainly manifested in the sea level rise, which changes the habitat elevation and daily flooding time of coastal wetlands, and then affects the survival and distribution of coastal wetland ecosystems.
Analysis of wave shoaling and shore-breakers on a low tide terrace beach based on in-situ measurements at Xisha Bay on South China coast
Yuan Li, Chi Zhang, Hongshuai Qi, Jiacheng Song, Weiqi Dai, Shanhang Chi, Jian Shi, Dake Chen
2023, 42(7): 175-184.   doi: 10.1007/s13131-023-2188-4
[Abstract](120) [FullText HTML](51) [PDF 3119KB](12)
Low tide terrace beach is a main beach type along South China coasts with strong tidal actions. How strong tides affect wave transformations on low tide terrace beach still remains unclear. In this study, in-situ measurements are conducted on the low terrace beach at Xisha Bay to provide quantitative descriptions of wave shoaling and shore-breaker phenomena under the tidal effects. It is found that wave breaking is unsaturated on the low tide terrace beach at Xisha Bay. Magnitudes of wave skewness and asymmetry increase as wave shoals and achieve the maximum value at the shore-breaker, and then decrease rapidly. Mean energy dissipation rates of shore-breakers are tide-modulated since the bottom slope changes at the shoreward boundary of wave propagation in a tidal cycle. The remaining wave energy flux at the initialization of the shore-breaker is 1%–12% of offshore wave energy flux, and the energy flux ratio decreases with increasing offshore wave heights. Wave attenuation at shore-breakers can be estimated directly from offshore wave conditions based on findings in this study, favoring designs of seawalls or beach nourishment projects. Field datasets on wave transformations can also be used for verifications of wave numerical models.
Effect of fence opening configurations on dune development
Qingqian Ning, Bailiang Li, Changmao Zhou, Yanyu He, Jianhui Liu
2023, 42(7): 185-193.   doi: 10.1007/s13131-023-2192-8
[Abstract](111) [FullText HTML](49) [PDF 1417KB](15)
Fences have been widely used in coastal protection engineering for their low cost, simple deployment, and easy integration with ecosystems. The effects of fence porosity and height on dune development have been investigated while not much attention has been paid to the effects of fence opening configurations, such as opening size and geometry, and porosity distributions. In this study, we deployed eight fences with same height and similar porosity, but different opening configurations on a sandy beach in Pingtan, Fujian Province. Results indicate that there is a similar two-dune-one-trough pattern for all fences at the beginning of dune development, and opening size, orientation, and geometry, and porosity distribution control the leeward dune peak locations. Fences with small openings and non-uniform porosity have high trapping efficiency, and upper denser porosity may be the optimal design as these fences have the highest trapping efficiency and capacity. The conclusions from this study can provide guidance on practical fence design.

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