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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](0) [FullText HTML](0)
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.
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/s13131-022-2096-z
[Abstract](91) [FullText HTML](29)
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.
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](20) [FullText HTML](8)
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.
Petrographical and mineral chemistry evidence to delineate the source/s of the Central Indian Ocean Basin pumices
Niyati G. Kalangutkar, Sridhar D. Iyer
 doi: 10.1007/s13131-022-2062-9
[Abstract](119) [FullText HTML](32) [PDF 3912KB](6)
We present data pertaining to mineral assemblages and composition of the Central Indian Ocean Basin (CIOB) pumices. Eight groups of pumices were identified considering the presence of phenocrysts of plagioclase, clinopyroxene, orthopyroxene, hornblende and biotite together with the occurrence of quartz and glass. Pigeonite, fayalite and ulvospinelare reported for the first time from these pumices. In the eight groups the modal percentage of the constituents are phenocrysts 3% to 19% (avg 9.6%), silicic glass 33% to 54% (avg 43%) and the rest is vesicles. Based on the above factors we have identified the possible sources of the CIOB pumices. The mineral compositions of plagioclase, pyroxenes, and biotite of the CIOB pumices were compared with those of Krakatau and Toba. Most of the plagioclase and pyroxene compositions resemble the Haranggoal Dacite Tuff of Toba and Krakatau. Considering the mineral assemblages and compositions there are pumices which do not correlate to any of the above eruptions and are probably from yet unidentified source/s. These sources could either be from nearby terrestrial volcanoes or intraplate seamounts present in the CIOB. In a global context, it is viable that petrological characteristics could be used as initial criteria to determine the source of pumices that occur at abyssal depths in the world ocean.
Mineralogy and geochemistry of hydrothermal sulphide from a submarine volcanic high at 18°36.4'S Central Lau Spreading Center, Southwest Pacific
Durbar Ray, Anil L. Paropkari
 doi: 10.1007/s13131-022-2121-2
[Abstract](105) [FullText HTML](25) [PDF 2366KB](8)
We report the mineralogy and geochemistry of hydrothermal sulphide from the crater of a volcanic high near 18°36.4′S of the Central Lau Spreading Center. During 1990s, that volcanic structure was reported active and sulphide samples were collected by MIR submersible. A section of a chimney-like structure from the crater-floor was studied here. The Fe-depleted sphalerites, and Co-depleted pyrites in that chimney were similar to those commonly found in low to moderate temperature (<300℃) sulphides from sediment-starved hydrothermal systems. Bulk analyses of three parts of that chimney section showed substantial enrichment of Zn (18%–20%) and Fe (14%–27%) but depletion of Cu (0.8%–1.3%). In chondrite-normalized rare earth element-patterns, the significant negative Ce-anomalies (Ce/Ce*=0.27–0.39) and weakly positive Eu-anomalies (Eu/Eu*=1.6–1.68) suggested sulphide mineralisation took place from reduced low-temperature fluid. The depleted concentration of lithophiles in this sulphide indicates restricted contribution of sub-ducting plate in genesis of source fluid as compared to those from other parts of Lau Spreading Centre. Uniform mineralogy and bulk composition of subsamples across the chimney section suggests barely any alteration of fluid composition and/or mode of mineralisation occurred during its growth.
Classification of ice and water in the Arctic using radar altimeter and microwave radiometer data from HY-2B satellite
Chengfei Jiang, Mingsen Lin, Ruixue Cao, Hao Wei, Lijian Shi, Bin Cheng, Yongjun Jia, Qimao Wang
 doi: 10.1007/s13131-022-2067-4
[Abstract](73) [FullText HTML](24) [PDF 5842KB](2)
Several Chinese marine satellites have been launched in recent years. Monitoring sea ice and the ocean in the Arctic is of great importance for climate research. Sea ice in the Arctic has changed rapidly during the past few decades with respect to the extent and thickness. In this study, we applied combined passive and active microwave data from the Chinese HaiYang-2B (HY-2B) satellite to classify ice and sea water in the Arctic. We use data from a radar altimeter (RA) and a microwave radiometer for atmospheric correction (CMR) to discriminate between ice and water by applying several approaches (1) the single parameter threshold criteria, (2) the multi-parameters linear segmentations and (3) the K-means clustering. The results yielded by these methods were in good agreement (classification accuracy >95%) with the ocean and sea ice-satellite application facility products between November and April. For other months (May–October), however, the agreement was less good (lowest classification accuracy approximate 85% in summer). A hybrid approach combined with graphical ice edges detection and microwave radar waveform analysis is therefore developed. A visual comparison with SAR images suggested the hybrid approach results greatly improved the ice water discrimination in summer. This study demonstrated that multi-sensors (RA and CMR) configurations from HY satellites can offer comparable polar earth observation to the European Space Agency and NOAA satellite products.
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](28) [FullText HTML](8)
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](185) [FullText HTML](76)
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.
Using radium isotopes to evaluate the uncertainty of submarine groundwater discharge in the northeast and entirety of the Daya Bay
GU Hequan, ZHAO Feng, NI Zhixin, WU Meigui, ZHAO Li, DANG Aicui, LI Dongmei, ZHANG Minxia, HU Qin
[Abstract](45) [FullText HTML](18)
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.
Features and factors of radium isotopes in Tianjin’s typical estuaries
Zhe Zhang, Yingchun Dong, Lixin Yi, Xin Hao, Yajie Zheng, Tianxue Lv
 doi: 10.1007/s13131-023-2146-1
[Abstract](72) [FullText HTML](28)
In order to characterize the features of radium isotopes in estuaries of Tianjin, a continuous survey and sampling of typical estuaries was 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.
Simulation of the transport mechanism of radium isotopes in the 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
[Abstract](71) [FullText HTML](32)
Naturally occurring Ra (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.
Subthermocline eddies carrying the Indonesian Throughflow water observed in the southeastern tropical Indian Ocean
Guangbing Yang, Quanan Zheng, Xuejun Xiong
 doi: 10.1007/s13131-022-2085-2
[Abstract](117) [FullText HTML](39)
We observed a subthermocline eddy (STE) with a cold and fresh core during an observation cruise along a transect of 10°S in the southeastern tropical Indian Ocean (SETIO) in December 2017. The vertical scale, speed radius, and maximum swirl velocity of the STE were about 200 m, 55 km, and 0.5 m/s, respectively. The mean Rossby number and Burger umber of the STE were then estimated to be about −0.7 and 2.4, indicating the STE was a submesoscale coherent vortex. The STE core water had characteristics of the Indonesian Throughflow (ITF) water and was distinct from that of surrounding areas. By examining Argo float data, another STE was well captured by five successive profiles of the same Argo float. Both STEs showed significant temperature and salinity anomalies at the σ0=26.0–26.5 kg/m3 surfaces. With the assumption that the low-salinity ITF water parcels could be carried only by surface eddies and the STEs, the Argo profiles, which detected low-salinity ITF water and were located outside a surface eddy, were believed to be inside an STE and were used to analyze the distribution, origin, and generation mechanism of the STE. The results suggested that the STEs carrying ITF water may be generated under topography-current interaction at the eastern coastal waters or under front-induced subduction in the area away from coastal waters. Those STEs may be widely distributed in the SETIO and may play a role in ITF water parcel transport.
Sea spray induced air-sea heat and salt fluxes based on the wave-steepness-dependent sea spray model
Xingkun Xu, Joey J. Voermans, Changlong Guan, Alexander V. Babanin
 doi: 10.1007/s13131-022-2073-6
[Abstract](128) [FullText HTML](46)
Sea spray, which comprises amounts of small ocean droplets, plays a significant role in the air-sea coupling, atmospheric and oceanic dynamics, and climate. However, it remains arduous to arrive at estimates for the efficiency and accuracy of the sea spray induced air-sea heat and salt fluxes. This is because the microphysical process of sea spray evolution in the air is of extreme complexity. In this study, we iteratively calculated the sea spray induced air-sea heat and salt fluxes at various weather condition. To do so, we implemented one novel wave-steepness-dependent sea spray model into a bulk air-sea fluxes algorithm and utilized other sea spray models as comparisons. Based on the improved wave-dependent bulk turbulent algorithm, we observed that despite the negative contribution of sea spray to the sensible heat fluxes, the sea spray positively contributes to the air-sea latent heat fluxes, leading to an overall increase in the total air-sea heat fluxes. The additional heat fluxes caused by sea spray may be the missing critical process that can clarify the discrepancies observed between measured and modelled Tropical Cyclone’s development and intensification. In addition to heat fluxes, we observed that sea spray has significant impacts on the air-sea salt fluxes. As the sea salt particles are one of the main sources of the atmosphere aerosol, our results imply that sea spray could impact global and regional climate. Thus, given the significance of sea spray on the air-sea boundary layer, sea spray effects need to be considered in studies of air-sea interaction, dynamics of atmosphere and ocean.
Genesis, evolution and reservoir identification of a Neogene submarine channel in the southwestern Qiongdongnan Basin, South China Sea
Shuo Chen, Donghui Jiang, Renhai Pu, Yunwen Guan, Xiaochuan Wu, Tianyu Ji, Chuang Liu
 doi: 10.1007/s13131-022-2071-8
[Abstract](149) [FullText HTML](43) [PDF 14435KB](7)
A rarely reported middle−late Miocene−Pliocene channel (incised valley fill), the Huaguang Channel (HGC), has been found in the deep-water area of the southwestern Qiongdongnan Basin (QDNB). This channel is almost perpendicular to the orientation of another well-known, large, and nearly coeval submarine channel in this area. Based on the interpretation of high-resolution 3D seismic data, this study describes and analyzes the stratigraphy, tectonics, sedimentation, morphology, structure and evolution of HGC by means of well-seismic synthetic calibration, one- and two-dimensional forward modeling, attribute interpretation, tectonic interpretation, and gas detection. The HGC is located on the downthrown side of an earlier activated normal fault and grew northwestward along the fault strike. The channel is part of a slope that extends from the western Huaguang Sag to the eastern Beijiao Uplift. The HGC underwent four developmental stages: the (1) incubation (late Sanya Formation, 20.4–15.5 Ma), (2) embryonic (Meishan Formation, 15.5–10.5 Ma), (3) peak (Huangliu Formation, 10.5–5.5 Ma) and (4) decline (Yinggehai Formation, 5.5–1.9 Ma) stages. The channel sandstones have a provenance from the southern Yongle Uplift and filled the channel via multistage vertical amalgamation and lateral migration. The channel extended 42.5 km in an approximately straight pattern in the peak stage. At 10.5 Ma, sea level fell relative to its lowest level, and three oblique progradation turbidite sand bodies filled the channel from south to north. A channel sandstone isopach map demonstrated a narrow distribution in the early stages and a fan-shaped distribution in the late stage. The formation and evolution of the HGC were controlled mainly by background tectonics, fault strike, relative sea level change, and mass supply from the Yongle Uplift. The HGC sandstone reservoir is near the Huaguangjiao Sag, where hydrocarbons were generated. Channel-bounding faults and underlying faults link the source rock with the reservoir. A regionally extensive mudstone caprock overlies the channel sandstone. Two traps likely containing gas were recognized in a structural high upstream of the channel from seismic attenuation anomalies. The HGC will likely become an important oil and gas accumulation setting in the QDNB deep-water area.
Dramatical hydro-sedimentary changes induced by bamboo fences over mangrove tidal flat of the largest delta in Beibu Gulf, Southwest China
Zuming Huang, Zhijun Dai, Riming Wang, Xiaoyan Zhou, Wenhong Pang, Jiejun Luo, Bingbin Feng, Baoqing Hu
 doi: 10.1007/s13131-022-2117-y
[Abstract](56) [FullText HTML](18)
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 (A. 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 SSC 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.
Impacts of human activities on morphological evolution in the Modaomen Estuary, China
Tiehan Liao, Haigang Zhan, Xing Wei, Weikang Zhan
 doi: 10.1007/s13131-022-2064-7
[Abstract](92) [FullText HTML](25) [PDF 4727KB](6)
The morphology of the Modaomen Estuary (ME) has undergone drastic changes in recent decades, and quantifying the contribution of human activities and natural processes is crucial for estuary management. Using Landsat images, chart data, and hydrological and meteorological data, this study analyzed the evolution of the shoreline and subaqueous topography of the ME and attempted to quantify the extent of the contributions of human activities. The results show that local human activities dominated morphological evolution in some periods. From 1973 to 2003, the shoreline advanced rapidly seaward, resulting in approximately half of the water area being converted into land. Human activity is critical to this process, with the direct contribution of local land reclamation projects reaching more than 85%. After 2003, the shoreline remained relatively stable, probably due to a decrease in land reclamation projects. Regarding the evolution of subaqueous topography, the shoals in the estuary were heavily silted and gradually disappeared during 1983–2003, and the waterways narrowed and deepened. The average siltation rate decreased from 15.43 mm/a to −1.02 mm/a, indicating that the ME changed from sedimentation to slight erosion. By detecting variations of sediment load, we found that upstream human activities reduced river sediment, while downstream human activities significantly increased sediment input to the ME, leaving little change in the actual sediment input to the ME for a relatively long period. In addition, based on the empirical relationship between the sediment input and siltation rate, local human activities influenced the shift in the siltation state more than upstream and downstream human activities did. These findings suggest that more attention should be paid to local human activities to improve the estuarine management in the ME.
Arctic sea ice volume export through the Fram Strait: variation and its effect factors
Haili Li, Changqing Ke, Qinghui Zhu, Xiaoyi Shen
 doi: 10.1007/s13131-022-2075-4
[Abstract](88) [FullText HTML](31)
Arctic sea ice export is important for the redistribution of freshwater and sea ice mass. Here, we use the sea ice thickness, sea ice velocity, and sea ice concentration (SIC) to estimate the exported sea ice volume through the Fram Strait from 2011 to 2018. We further analyse the contributions of the sea ice thickness, velocity and concentration to sea ice volume export. Then, the relationships between atmospheric circulation indices (Arctic Oscillation (AO), North Atlantic Oscillation (NAO), and Arctic Dipole (AD)) and the sea ice volume export are discussed. Finally, we analyse the impact of wind-driven oceanic circulation indices (Ekman transport (ET)) on the sea ice volume export. The sea ice volume export rapidly increases in winter and decreases in spring. The exported sea ice volume in winter is likely to exceed that in spring in the future. Among sea ice thickness, velocity and SIC, the greatest contribution to sea ice export comes from the ice velocity. The exported sea ice volume through the zonal gate of the Fram Strait (which contributes 97% to the total sea ice volume export of the Fram Strait) is much higher than that through the meridional gate (3%) because the sea ice flowing out of the zonal gate has the characteristics of a high thickness (mainly thicker than 1 m), a high velocity (mainly faster than 0.06 m/s) and a high concentration (mainly higher than 80%). The AD and ET explain 53.86% and 38.37% of the variation in sea ice volume export, respectively.
Physical-mechanical properties of sediments and their correlation with near seafloor seismic amplitude in the Liwan canyon area, northern South China Sea
Jie Liu, Lejun Liu, Ping Li
 doi: 10.1007/s13131-022-2069-2
[Abstract](99) [FullText HTML](26) [PDF 1077KB](16)
Before the implementation of offshore oil and gas exploitation, it is essential to understand the various factors that influence the stability of submarine sediments surrounding the project. Considering the factors such as cost and operability, it is not feasible to assess the physical-mechanical properties of sediments covering the entire region by borehole sampling. In this study, the correlation between near seafloor seismic amplitude and the mean shear strength of shallow sediments was explored using seismic and core testing data from the northern continental slope area of the South China Sea. Results showed that the mean water content of sediments in the layer up to 12 m below the seafloor (mbsf) gradually increased with increasing water depth, and the mean shear strength tended to decrease rapidly near the 1 000 m depth contour. The near seafloor seismic amplitude could reflect the mean shear strength of sediments in the 12 mbsf layer under seismic frequency of 65 Hz and wave velocity of 1 600 m/s. When the mean shear strength was greater than 10 kPa or the water depth was less than 1 000 m, there was a significant linear positive correlation between mean shear strength and near seafloor seismic amplitude. Otherwise, there was a significant linear negative correlation between mean shear strength and near seafloor seismic amplitude. On the basis of these correlations, the pattern of shear strength was estimated from near seafloor seismic amplitude and mapped. The mean shear strength of sediments above 12 mbsf gradually decreased with increasing water depth in the continental slope area, whereas little change occurred in the continental shelf and the end of the canyon. Within the canyon area, the mean shear strength of sediments was characterized by larger values in both sides of the canyon walls and smaller values in the canyon bottom, which was consistent with the infinite slope stability theory. The study provides a method for using near seafloor seismic amplitude data to guide sediment sampling design, and presents a continuous dataset of sediment strength for the simulation of regional sediment stability.
Shallow water bathymetry based on a back propagation neural network and ensemble learning using multispectral satellite imagery
Sensen Chu, Liang Cheng, Jian Cheng, Xuedong Zhang, Jie Zhang, Jiabing Chen, Jinming Liu
 doi: 10.1007/s13131-022-2065-6
[Abstract](126) [FullText HTML](48)
The back propagation (BP) neural network method is widely used in bathymetry based on multispectral satellite imagery. However, the classical BP neural network method faces a potential problem because it easily falls into a local minimum, leading to model training failure. This study confirmed that the local minimum problem of the BP neural network method exists in the bathymetry field and cannot be ignored. Furthermore, to solve the local minimum problem of the BP neural network method, a bathymetry method based on a BP neural network and ensemble learning (BPEL) is proposed. First, the remote sensing imagery and training sample were used as input datasets, and the BP method was used as the base learner to produce multiple water depth inversion results. Then, a new ensemble strategy, namely the minimum outlying degree method, was proposed and used to integrate the water depth inversion results. Finally, an ensemble bathymetric map was acquired. Anda Reef, northeastern Jiuzhang Atoll, and Pingtan coastal zone were selected as test cases to validate the proposed method. Compared with the BP neural network method, the root-mean-square error and the average relative error of the BPEL method can reduce by 0.65–2.84 m and 16%–46% in the three test cases at most. The results showed that the proposed BPEL method could solve the local minimum problem of the BP neural network method and obtain highly robust and accurate bathymetric maps.
Characteristics and mechanisms of the intraseasonal variability of sea surface salinity in the southeastern Arabian Sea during 2015–2020
Hui Teng, Yun Qiu, Xinyu Lin, Xiwu Zhou
 doi: 10.1007/s13131-022-2074-5
[Abstract](124) [FullText HTML](37) [PDF 3735KB](13)
Based on Soil Moisture Active Passive sea surface salinity (SSS) data from April 2015 to August 2020, combined with Objectively Analyzed Air-Sea Heat Flux and other observational data and Hybrid Coordinate Ocean Model (HYCOM) model data, this work explores the characteristics and mechanisms of the intraseasonal variability of SSS in the southeastern Arabian Sea (SEAS). The results show that the intraseasonal variability of SSS in the SEAS is very significant, especially the strongest intraseasonal signal in SSS, which is located along the northeast monsoon current (NMC) path south of the Indian Peninsula. There are remarkable seasonal differences in intraseasonal SSS variability, which is very weak in spring and summer and much stronger in autumn and winter. This strong intraseasonal variability in autumn and winter is closely related to the Madden-Julian Oscillation (MJO) event during this period. The northeast wind anomaly in the Bay of Bengal (BOB) associated with the active MJO phase strengthens the East India Coastal Current and NMC and consequently induces more BOB low-salinity water to enter the SEAS, causing strong SSS fluctuations. In addition, MJO-related precipitation further amplifies the intraseasonal variability of SSS in SEAS. Based on budget analysis of the mixed layer salinity using HYCOM data, it is shown that horizontal salinity advection (especially zonal advection) dominates the intraseasonal variability of mixed layer salinity and that surface freshwater flux has a secondary role.
Quantitative morphometric analysis of a deep-water channel in the Taranaki Basin, New Zealand
Wei Wu, Guangxu Wang, Changsong Lin, Weiqing Liu, Quan Li, Zhendong Feng, Shuyuan Ning
 doi: 10.1007/s13131-022-2024-2
[Abstract](151) [FullText HTML](36) [PDF 4248KB](12)
The morphological changes of deep-water channels have an important influence on the distributions of channel sand reservoirs, so it is important to explore the morphological change process of deep-water channel for the exploration and development of deep-water oil and gas. Based on a typical sinuous Quaternary channel (Channel I) in the Taranaki Basin, New Zealand, a variety of seismic interpretation techniques were applied to quantitatively characterize the morphological characteristics of the Channel I, and the relationships between the quantitative parameters and the morphological changes of the Channel I, as well as the controlling factors affecting those morphological changes, were discussed. The results are as follows: (1) in the quantitative analysis, six parameters were selected: the channel depth, width, sinuosity, and aspect ratio (width/depth), the channel swing amplitude (λ) and the channel bend frequency (ω); (2) according to the quantitative morphological parameters of the channel (mainly including three parameters such as channel sinuosity, ω and λ), the Channel I was divided into three types: the low-sinuous channel (LSC), the high-sinuous channel (HSC), the moderate-sinuous channel (MSC). U-shaped channel cross-sections developed in the LSC, V-shaped channel cross-sections developed in the HSC, including inclined-V and symmetric-V cross-sections, and dish-shaped channel cross-sections developed in the MSC; (3) the morphological characteristics of the LSC and MSC were related to their widths and depths, while the morphology of the HSC was greatly affected by the channel width, a change in depth did not affect the HSC morphology; (4) the morphological changes of the Channel I were controlled mainly by the slope gradient, the restricted capacity of the channel and the differential in fluid properties.
Evaluation of the submarine debris-flow hazard risks to planned subsea pipeline systems: case study in the Qiongdongnan Basin, South China Sea
Mingquan Huang, Xuesheng Qian, Jingping Xu, Xuecheng Li
[Abstract](69) [FullText HTML](26)
The ever-increasing deepwater oil and gas development in the Qiongdongnan Basin, South China Sea has initiated the need to evaluate submarine debris-flow hazard risks to seafloor infrastructures. This paper presents a case study on evaluating the debris-flow hazard risks to the planned pipeline systems in this region. We used a numerical model to perform simulations to support this quantitative evaluation. First, one relict failure interpreted across the development site was simulated. The back-analysis modeling was used to validate the applicability of the rheological parameters. Then, this model was applied to forecast the runout behaviors of future debris flows originating from the unstable upslope regions considered to be the most critical to the pipeline systems surrounding the manifolds A and B. The model results showed that the potential debris-flow hazard risks rely on the location of structures and the selection of rheological parameters. For the manifold B and connected pipeline systems, because of their remote distances away from unstable canyon flanks, the potential debris flows impose few risks. However, the pipeline systems around the manifold A are exposed to significant hazard risks from future debris flows with selected rheological parameters. These results are beneficial for the design of a more resilient pipeline route in consideration of future debris-flow hazard risks.
Seasonal variation of the shape and location of the Luzon cold eddy
Ruili Sun, Peiliang Li, Yanzhen Gu, Chaojie Zhou, Cong Liu, Lin Zhang
 doi: 10.1007/s13131-022-2084-3
[Abstract](55) [FullText HTML](12)
Using observational data from multiple satellites, we studied seasonal variations of the shape and location of the Luzon cold eddy (LCE) northwest of Luzon Island. The shape and location of the LCE have obvious seasonal variations. The LCE occurs, develops, and disappears from December-April of the next year. During this period, the shape of the LCE changed from a flat ellipse to a circular ellipse, and the change in shape can be reflected by the increase of the ellipticity of the LCE from 0.16 to 0.82. The latitude of center location of the LCE changes from 17.4°N to 19°N, and the change in latitude can reach 1.6°. Further study showed that seasonal variation of the northeast monsoon intensity leads to the change in the shape and location of the LCE. The seasonal variation of the LCE shape can significantly alter the spatial distribution of the thermal front and chlorophyll-a northwest of the Luzon Island by geostrophic advection.
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](67) [FullText HTML](27)
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](102) [FullText HTML](16)
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.
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
 doi: 10.1007/s13131-022-2126-x
[Abstract](118) [FullText HTML](32)
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.
Epipelagic mesozooplankton communities in the northeastern Indian Ocean off Myanmar during the winter monsoon
Ping Du, Dingyong Zeng, Feilong Lin, Sanda Naing, Zhibing Jiang, Jingjing Zhang, Di Tian, Qinghe Liu, Yuanli Zhu, Soe Moe Lwin, Wenqi Ye, Chenggang Liu, Lu Shou, Feng Zhou
 doi: 10.1007/s13131-022-2090-5
[Abstract](107) [FullText HTML](29)
The northern Andaman Sea off Myanmar is one of the relatively high productive regions in the Indian Ocean. The abundance, biomass and species composition of mesozooplankton and their relationships with environmental variables in the epipelagic zone (~200 m) were studied for the first time during the Sino-Myanmar joint cruise (February 2020). The mean abundance and biomass of mesozooplankton were 1916.7±1192.9 ind/m3 and 17.8±7.9 mg/m3, respectively. A total of 213 species (taxa) were identified from all samples. The omnivorous Cyclopoida Oncaea venusta and Oithona spp. were the top two dominant taxa. Three mesozooplankton communities were determined via cluster analysis: the open ocean in the Andaman Sea and the Bay of Bengal (BOB) (group A), the transition zone across the Preparis Strait (group B), and nearshore water off the Ayeyarwady Delta and along the Tanintharyi Coast (group C). Variation partitioning analysis (VPA) revealed that the interaction of physical and biological factors explained 98.8% of mesozooplankton community spatial variation, and redundancy analysis (RDA) revealed that column mean chlorophyll a (CMCHLA) was the most important explanatory variable (43.1%). The abundance and biomass were significantly higher in group C, the same as CMCHLA and column mean temperature (CMT) and in contrast to salinity, and CMT was the dominant factor. Significant taxon spatial variations were controlled by CMCHLA, salinity and temperature. This study suggested that mesozooplankton spatial variation was mainly regulated by physical processes through their effects on CMCHLA. The physical processes were simultaneously affected by heat loss differences, freshwater influx, eddies and depth.
Ecological evaluation of marine macroalgal communities on five Islands of Korea in the Yellow Sea
Su Jin Han, Jae-Gil Jang, Hyun-Jung Kim, Tae-Ho Seo, Joo Myun Park
 doi: 10.1007/s13131-022-2089-y
[Abstract](169) [FullText HTML](44)
Macroalgae have long been used as biological indicators of marine ecosystem health worldwide due to their ecological importance and sensitivity to environmental stress. A number of previous studies have utilized macroalgal communities in monitoring surveys of environmental conditions. This study examined the characteristics and patterns of marine macroalgal communities in the Yellow Sea off the western coast of Korea. Macroalgae were analyzed for the number of species, biomass, and coverage ratio (%) by macroalgal type. During the study period, 82 macroalgal species (ten green algae, 17 brown algae, and 55 red algae) were identified at the five study sites, with the highest number of species found at Gwanrido and Uido (both containing 41 species) and the lowest at Daeijakdo (27 species). The average biomass (via dry weight) was 98.63 g/m2, consisting of green algae (8.39 g/m2), brown algae (35.08 g/m2), and red algae (55.16 g/m2). The dominant macroalgae species in terms of biomass (g/m2) were Sargassum thunbergii, Corallina pilulifera, and Chondria atropurpurea in the intertidal zones, and Gelidium elegans and Sargassum miyabei in the subtidal zones. Richness, evenness, and diversity indices based on the biomass of abundant species were 5.08, 0.65, and 2.30, respectively, over the entire study area. Based on the evaluation of the environmental states by the community indices, overall, the ecological evaluation index (EEI-c) of macroalgae communities in the study area was marked as “Good-Moderate”, but was determined as “Moderate-Low” at several sites during summer. The results can be a direct approach in the assessment of coastal habitats in which anthropogenic as well as climate change influences persist.
Assessment of prediction model of the CPUE of neon flying squid with different sources of remote sensing data
Liang Chang, Yanli Yang, Xinjun Chen, Wei Yu, Yangdong Li, Guiping Feng, Yang Zhang
 doi: 10.1007/s13131-022-2049-6
[Abstract](171) [FullText HTML](58)
Accurately building the relationship between the oceanographic environment and the distribution of neon flying squid (Ommastrephes bartramii) is very important to understand the potential habitat pattern of O. bartramii. However, when building the prediction model of O. bartramii with traditional oceanographic variables (e.g., chlorophyll-a concentration (Chl-a) and sea surface temperature (SST)) from space-borne observations, part of the important spectrum characteristics of the oceanic surface could be masked by using the satellite data products directly. In this study, the neglected remote sensing information (i.e., spectral remote sensing reflectance (Rrs) and brightness temperature (BT)) is firstly incorporated to build the prediction model of catch per unit effort (CPUE) of O. bartramii from July to December during 2014–2018 in the Northwest Pacific Ocean. Results show that both the conventional oceanographic variables and the neglected remote sensing data are suitable for building the prediction model, whereas the overall root mean square error (RMSE) of the predicted CPUE of O. bartramii with the former is typically less accurate than that with the latter. Hence, the Rrs and BT could be a more suitable data source than the Chl-a and SST to predict the distribution of O. bartramii, highlighting that the potential value of the neglected variables in understading the habitat suitability of O. bartramii.
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](121) [FullText HTML](37)
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](190) [FullText HTML](55)
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](511) [FullText HTML](143)
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(4).  
[Abstract](42) [PDF 2045KB](7)
2023, 42(4).  
[Abstract](33) [FullText HTML](13) [PDF 65KB](7)
Articles$Physical Oceanography, Marine Meteorology and Marine Physics
Study of coexisting upstream solitary wave packet and downstream wakes induced by Diaoyu Dao and its affiliated islands detected by satellite sun glitter
Lina Cai, Xiaoqi Jiang, Xiaojun Yan, Yan Bai, Jianqiang Liu, Menghan Yu, Rong Tang, Jingjing Jiang
2023, 42(4): 1-15.   doi: 10.1007/s13131-022-2099-9
[Abstract](354) [FullText HTML](147) [PDF 7468KB](34)
Taking the advantage of sun glitter (SG) observed from high-resolution satellites Gaofen-1 (GF-1) and Gaofen-6 (GF-6), a new method named Shield and Vortex 1-2 (SAV1-2) for extracting spatial texture information from sun glitter was established. Sea surface texture detail information around Diaoyu Dao and its affiliated islands was extracted using SAV1-2. Meanwhile, the dynamic characteristics of the water environment were analyzed by combining the water color, temperature and dynamic data. The results show the following information. (1) Stable westward shield effect and eastward Karman vortex streets, extracted from SG, appear upstream (westward) and downstream (eastward) of the Diaoyu Dao and its affiliated islands respectively. (2) The dominant direction of the Kuroshio Current in the Diaoyu Dao and its affiliated islands area is east, the Diaoyu Dao and its affiliated islands interacting with Kuroshio, inducing western shield and eastern shelter and wake. Furthermore, wave intervals of the shield in front of the island range from hundreds to thousands of metres, and extend wider than the island itself. (3) Combining with high-resolution sea surface temperature (SST) and chlorophyll a (Chl a) concentration, the directional changes of water color elements are mutually supported and proved with the stable shield (wave packet) effect in the west and vortex street effect in the east. The change of SST upstream of the island (western shield area) is not significant, the temperature in the downstream shelter area decreases slightly, and the SST in the downstream wake area shows a general trend of obvious decrease. The wake area is dominated by Karman vortex streets in shape, supplementing by vortices. The concentration of Chl a in the west shield of island is as low as that in downstream shelter area, while it increases significantly in the downstream wake area with shape in eddy or ribbon. (4) The SAV methods of extracting sea surface texture detail using SG can be widely used in different sea areas and water quality. This paper can provide reference for the protection and development of Diaoyu Dao and its affiliated islands and its surrounding waters. It is suggested that some kind of current buffer, such as marine wind farm, should be established in the western waters of Diaoyu Dao and its affiliated islands to protect the islands, and marine pasture should be developed in the downstream of eastern waters of Diaoyu Dao and its affiliated islands.
Articles$Marine Chemistry
Sources and transformations of nitrite in the Amundsen Sea in summer 2019 and 2020 as revealed by nitrogen and oxygen isotopes
Yangjun Chen, Jinxu Chen, Yi Wang, You Jiang, Minfang Zheng, Yusheng Qiu, Min Chen
2023, 42(4): 16-24.   doi: 10.1007/s13131-022-2111-4
[Abstract](213) [FullText HTML](83) [PDF 1415KB](22)
In this study, the nitrogen and oxygen isotope compositions of nitrite in the upper 150 m water column of the Amundsen Sea in the summer of 2019 and 2020 were measured to reveal the distribution and transformation of nitrite in the euphotic zone of the Southern Ocean. We found that primary nitrite maxima (PNMs) are widely present in the Amundsen Sea, where the depth of occurrence deepens from east to west and nitrite concentrations increases. Evidence from dual isotopes suggests that the formation of PNMs in all regions of the Amundsen Sea is dominated by ammonia oxidation. More importantly, the nitrogen and oxygen isotope compositions of nitrite in the Amundsen Sea mixed layer are abnormal, and their depth profiles are mirror symmetrical. Isotopic anomalies exhibit spatial variations, with central surface water having the lowest nitrogen isotope composition (−89.9‰±0.2‰) and western surface water having the highest oxygen isotope composition (63.3‰±0.3‰). Isotopic exchange reaction between nitrate and nitrite is responsible for these isotope anomalies, as both nitrogen and oxygen isotopes have large isotopic fractionation and opposite enrichment effects. This proves that isotopic exchange reaction operates extensively in different regions of the Amundsen Sea. Our study highlights the unique role of dual isotopes of nitrite in deepening the understanding of nitrogen cycle. Further studies on ammonia oxidation and isotopic exchange between nitrate and nitrite are warranted in the future to understand their roles in the nitrogen cycle in the Southern Ocean.
Potential effects of sea level rise on the soil-atmosphere greenhouse gas emissions in Kandelia obovata mangrove forests
Jiahui Chen, Shichen Zeng, Min Gao, Guangcheng Chen, Heng Zhu, Yong Ye
2023, 42(4): 25-32.   doi: 10.1007/s13131-022-2087-0
[Abstract](124) [FullText HTML](35) [PDF 505KB](9)
Mangrove forests are under the stress of sea level rise (SLR) which would affect mangrove soil biogeochemistry. Mangrove soils are important sources of soil-atmosphere greenhouse gas (GHG) emissions, including carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O). Understanding how SLR influences GHG emissions is critical for evaluating mangrove blue carbon capability. In this study, potential effects of SLR on the GHG emissions were quantified through static closed chamber technique among three sites under different intertidal elevations, representing tidal flooding situation of SLR values of 0 cm, 40 cm and 80 cm, respectively. Compared with Site SLR 0 cm, annual CO2 and N2O fluxes decreased by approximately 75.0% and 27.3% due to higher soil water content, lower salinity and soil nutrient environments at Site SLR 80 cm. However, CH4 fluxes increased by approximately 13.7% at Site SLR 40 cm and 8.8% at Site SLR 80 cm because of lower salinity, higher soil water content and soil pH. CO2-equivalent fluxes were 396.61 g/(m2·a), 1423.29 g/(m2·a) and 1420.21 g/(m2·a) at Sites SLR 80 cm, SLR 40 cm and SLR 0 cm, respectively. From Site SLR 0 cm to Site SLR 80 cm, contribution rate of N2O and CH4 increased by approximately 7.42% and 3.02%, while contribution rate of CO2 decreased by approximately 10.44%. The results indicated that warming potential of trace CH4 and N2O was non-negligible with SLR. Potential effects of SLR on the mangrove blue carbon capability should warrant attention due to changes of all three greenhouse gas fluxes with SLR.
Sedimentary nitrogen dynamics in a coastal reef area with relatively high nitrogen concentration
Zhiming Ning, Ronglin Xia, Bin Yang, Cao Fang, Wei Jiang, Guodong Song
2023, 42(4): 33-40.   doi: 10.1007/s13131-022-2088-z
[Abstract](275) [FullText HTML](110) [PDF 725KB](25)
The migration and transformation of nitrogen (N) in sediments play an important role in regulating the N concentration and nutrient structures in shallow seas. However, studies of sedimentary N dynamics are rarely focused on carbonate sediments, although these account for about 40% of the continental shelf area. Thus, the regulation mechanisms of the N dynamics in the carbonate sands of coral reefs are not clear. Taking the coral reef area of Weizhou Island, which has a relatively high N concentration, as the research object, we conducted a series of flow-through reactor experiments to investigate the fluxes of different N forms at the interface of sediment and seawater and their regulation mechanism by environmental factors. The fluxes of dissolved inorganic and organic N (DIN and DON) at different stations were −0.39–0.12 mmol/(m2·h) and −0.18–0.39 mmol/(m2·h), respectively. Denitrification (0.11–0.25 mmol/(m2·h)) was closely coupled to nitrification, which was limited by the availability of organic matter and its degradation product (i.e., \begin{document}${\rm{NH}}_4^+ $\end{document}). Thus, the excessive \begin{document}${\rm{NO}}_3^– $\end{document} might be reduced to \begin{document}${\rm{NH}}_4^+ $\end{document} by dissimilatory nitrate reduction to ammonium, rather than to N2 by denitrification. \begin{document}${\rm{NO}}_3^– $\end{document} reduction peaked at intermediate advection rates (96 L/(m2·h)) and flow path lengths (10 cm), but the release of DON also peaked at the same condition. In addition, climate warming would significantly affect sedimentary N dynamics at Weizhou Island. These results may help address the broader issue of the N cycle in coral reef ecosystems under the dual pressure of climate warming and anthropogenic activities, and these results are beneficial to coral reef protection and local ecological management.
A comparison between high temperature catalytic and persulfate oxidation for the determination of total dissolved nitrogen in natural waters
Tiantian Ge, Xue Yang, Shan Jiang, Liju Tan
2023, 42(4): 41-49.   doi: 10.1007/s13131-022-2035-z
[Abstract](139) [FullText HTML](42) [PDF 1222KB](6)
Total dissolved nitrogen (TDN) is an important parameter for assessing the nutrient cycling and status of natural waters. The accurate determination of TDN in natural waters is essential for assessing its contents and distinguishing different forms of nitrogen in the water. The TDN in various systems has been largely documented, and the concentrations of TDN are usually obtained using high-temperature catalytic (HTC) or persulfate oxidation (PO). However, the accuracy of these methods and their suitability for all types of natural waters are still unclear. To explore both methods in-depth, assorted samples were tested, including eight solutions composed of nitrogen-containing compounds (3 dissolved inorganic nitrogen fractions: \begin{document}${{\rm {NO}}_3^-}$\end{document}, \begin{document}${{\rm {NO}}_2^-} $\end{document} and \begin{document}${{\rm {NH}}_4^+} $\end{document}; 5 organic compounds: EDTA-2Na, vitamin B1, vitamin B12, amino acids, and urea) and 105 natural waters which were collected from an open ocean (Northwest Pacific Ocean, 28), a marginal sea (Yellow Sea, 34), an estuary (Huanghe River mouth, 31), rivers (Huanghe River, 4; Licun River, 4), and precipitations (4 samples). The results showed that heterocycles and molecular dimensions had certain effects on the oxidation efficiency of the PO method but had little effect on HTC. There was no significant difference between the two methods for natural waters, but HTC was more suitable for deep-sea samples with low TDN concentrations (less than 10 μmol/L) and low organic activity. Overall, HTC has a relatively simple measurement process, a high degree of automation, and low error. Therefore, HTC can be recommended to determine the TDN of samples in freshwater and seawater.
The impacts of ambiguity in preparation of 80% sulfuric acid solution and shaking time control of calibration solution on the determination of transparent exopolymer particles
Congcong Guo, Guicheng Zhang, Shan Jian, Wei Ma, Jun Sun
2023, 42(4): 50-58.   doi: 10.1007/s13131-023-2182-x
[Abstract](116) [FullText HTML](34) [PDF 883KB](7)
The quantification of transparent exopolymer particles (TEP) by colorimetric method is of large error and low repeatability, one major reason of which is related to the absence of clear definition and evaluation for part steps of the original method. It is obscure that the 80% sulfuric acid solution, acted as the extraction solution in the determination of TEP, is prepared based on a volume ratio or mass ratio. Furthermore, the change of solubility of recently available Gum Xanthan (GX) from the market means that the original protocol is no longer applicable, and the grinding of GX stock solution with a tissue grinder is replaced by shaking with a rotating shaker in the study to prevent the excessive dissolution of GX. We found that different preparation techniques could result in the varied concentrations of 80% H2SO4. The duration of shaking during the preparation of standard solution significantly affected the slope of the calibration curve, which caused different correction results of TEP. The impacts of different extraction solution concentrations and shaking time of GX solution on the quantification of TEP were investigated based on the field sampling and laboratory analysis. The extraction capacities of H2SO4 with different concentrations for Alcian Blue were distinct, but had limited effect on the final measuring result of TEP. The change of the standard curve slope came along with the variation of shaking time, which markedly altered the detection limit and calibration result, and the extended shaking time was in favor of the determination of low-concentration TEP. It was suggested that the extraction solution concentration, shaking time and filtration volume of standard solution are required to be well controlled and selected to obtain more accurate results for TEP with different concentrations.
Articles$Marine Biology
Impact of climate change on potential habitat distribution of Sciaenidae in the coastal waters of China
Wen Yang, Wenjia Hu, Bin Chen, Hongjian Tan, Shangke Su, Like Ding, Peng Dong, Weiwei Yu, Jianguo Du
2023, 42(4): 59-71.   doi: 10.1007/s13131-022-2053-x
[Abstract](211) [FullText HTML](64) [PDF 4410KB](29)
Climate change has affected and will continue to affect the spatial distribution patterns of marine organisms. To understand the impact of climate change on the distribution patterns and species richness of the Sciaenidae in China’s coastal waters, the maximum entropy model was used to combine six environmental factors and predict the potential distribution of 12 major species of Sciaenidae by 2050s under Representative Concentration Pathways (RCPs) 2.6 and 8.5. The results showed that the average area under the receiver operating characteristic curve of the model was 0.917, indicating that the model predictions were accurate and reliable. The main driving factors affecting the potential distribution of these fishes were dissolved oxygen, salinity, and sea surface temperature (SST). There was an overall northward shift in the potential habitat areas of these fishes under the two climate scenarios. The total potential habitat areas of Larimichthys polyactis, Pennahia argentata, and Pennahia pawak decreased under both climate scenarios, while the total habitat area of Johnius belengerii, Pennahia anea, Miichthys miiuy, Collichthys lucidus, and Collichthys niveatus increased, suggesting that these might be loser and winner species, respectively. The expansion rate, contraction rate, degree of centroid change, and species richness in the potential habitats were generally more significant under RCP8.5 than RCP2.6. The mean shift rates of the potential distribution were 41.50 km/(10 a) and 29.20 km/(10 a) under RCP8.5 and RCP2.6, respectively. The changes in Sciaenidae species richness under climate change were bounded by the Changjiang River Estuary waters, with obvious north-south differences. Some waters with increased species richness may become refuges for Sciaenidae fishes under climate change. The richness and habitat area change rate of some aquatic germplasm resources will decrease, meanings that these reserves are more sensitive to climate change, and more attention should be paid to the potential challenges and opportunities for fishery managers. This study may provide a scientific basis for the management and conservation of Sciaenidae in China under climate change.
Discordant patterns of genetic variation between mitochondrial and microsatellite markers in Acanthogobius ommaturus across the coastal areas of China
Chenyu Song, Zhong Tu, Na Song
2023, 42(4): 72-80.   doi: 10.1007/s13131-022-2042-0
[Abstract](169) [FullText HTML](48) [PDF 1006KB](9)
Acanthogobius ommaturus, which belongs to the family Gobiidae, is a euryhaline and demersal fish that is widely distributed in the coastal areas, harbors, and estuaries of China, D. P. R. Korea and Japan. In this study, the genetic diversity and genetic structure of five geographical populations of A. ommaturus was assessed using the mitochondrial hypervariable region gene and microsatellite markers. The results of the two genetic markers indicated that the A. ommaturus populations had a high level of genetic diversity. The mitochondrial marker detected weak genetic differentiation among populations, and the Neighbor-Joining tree showed that there was no obvious pedigree branches and geographic structure as well. However, population of Zhoushan showed significant genetic differentiation with other populations by microsatellite markers. The population of A. ommaturus has not experienced bottleneck effect recently. We speculated that the Pleistocene climate change and juvenile fish dispersal played an important role in the population differentiation of A. ommaturus.
Two complete mitogenomes of Ocypodoidea (Decapoda: Brachyura), Cleistostoma dilatatum (Camptandriidae) and Euplax sp. (Macrophthalmidae) and its phylogenetic implications
Ying Zhang, Liming Wei, Bingjian Liu, Liqin Liu, Zhenming Lü, Li Gong
2023, 42(4): 81-92.   doi: 10.1007/s13131-022-2054-9
[Abstract](189) [FullText HTML](58) [PDF 1332KB](10)
Complete mitochondrial genomes (mitogenomes) can provide useful information for phylogenetic relationships, gene rearrangement, and molecular evolution. In the present study, two newly sequenced mitogenomes of Ocypodoidea (Cleistostoma dilatatum and Euplax sp.) were reported for the first time, which are 15 444 bp and 16 129 bp in length, respectively. Cleistostoma dilatatum is the first species in the family Camptandriidae whose complete mitogenome was sequenced. Each mitogenome contains an entire set of 37 genes and a putative control region, but their gene arrangements are largely different. Tandem duplication and random loss model is proposed to account for their gene arrangements. Comparative genomic analyses of 19 mitogenomes clustering in one branch reveal that 18 of them shared the same gene rearrangement, while that of C. dilatatum mitogenome was consistent with the ancestral gene arrangement of Brachyura. The dN/dS ratio analysis shows that all PCGs are evolving under purifying selection. Phylogenetic analyses show that all Macrophalmidae species cluster together as a group, and then form a sister clade with Camptandriidae. Moreover, the polyphyly of three superfamilies (Ocypodoidea, Eriphioidea, and Grapsoidea) is reconfirmed. These findings help to confirm the phylogenetic position of Camptandriidae, as well as provide new insights into the phylogeny of Brachyura.
Ensemble habitat suitability modeling of stomatopods with Oratosquilla oratoria as an example
Lisha Guan, Xianshi Jin, Tao Yang, Xiujuan Shan
2023, 42(4): 93-102.   doi: 10.1007/s13131-022-2051-z
[Abstract](93) [FullText HTML](35) [PDF 2144KB](3)
Stomatopods are better known as mantis shrimp with considerable ecological importance in wide coastal waters globally. Some stomatopod species are exploited commercially, including Oratosquilla oratoria in the Northwest Pacific. Yet, few studies have published to promote accurate habitat identification of stomatopods, obstructing scientific management and conservation of these valuable organisms. This study provides an ensemble modeling framework for habitat suitability modeling of stomatopods, utilizing the O. oratoria stock in the Bohai Sea as an example. Two modeling techniques (i.e., generalized additive model (GAM) and geographical weighted regression (GWR)) were applied to select environmental predictors (especially the selection between two types of sediment metrics) that better characterize O. oratoria distribution and build separate habitat suitability models (HSM). The performance of the individual HSMs were compared on interpolation accuracy and transferability. Then, they were integrated to check whether the ensemble model outperforms either individual model, according to fishers’ knowledge and scientific survey data. As a result, grain-size metrics of sediment outperformed sediment content metrics in modeling O. oratoria habitat, possibly because grain-size metrics not only reflect the effect of substrates on burrow development, but also link to sediment heat capacity which influences individual thermoregulation. Moreover, the GWR-based HSM outperformed the GAM-based HSM in interpolation accuracy, while the latter one displayed better transferability. On balance, the ensemble HSM appeared to improve the predictive performance overall, as it could avoid dependence on a single model type and successfully identified fisher-recognized and survey-indicated suitable habitats in either sparsely sampled or well investigated areas.
Phytoplanktonic biogeography in the subtropical coastal waters, East China Sea along intensive anthropogenic stresses: roles of environmental versus spatial factors
Ran Ye, Haibo Zhang, Yige Yu, Qing Xu, Dandi Shen, Min Ren, Lian Liu, Yanhong Cai
2023, 42(4): 103-113.   doi: 10.1007/s13131-022-2086-1
[Abstract](92) [FullText HTML](24) [PDF 3053KB](4)
Understanding the relative roles of local environmental effects and spatial effects on phytoplankton community is of essential importance to study the biogeography of them at regional scale. However, the determinants that driving the biogeography of phytoplankton communities in the coastal area of northern Zhejiang still remained unclear. We surveyed phytoplankton community compositions in water columns associated with environmental and spatial influences across five subzones that geographically covering this region over four seasons. Diatoms and dinoflagellates were recorded as the main dominant groups and Coscinodiscus oculs-iridis, Coscinodiscus jonesianus, and Skeletonema costatum, were identified as the major abundant species existing in all seasons. Spatially structured environmental conditions, rather than pure spatial or environmental factors, substantially shaped the biogeography of phytoplankton community, with the former mainly comprised of water temperature, dissolved oxygen, phosphate, pH, and salinity, and the latter referring to a non-negligible factor. This study was the first integrated research that combining environmental filtering with spatial factors in structuring phytoplankton communities at a complete tempo-spatial scale. Our results may facilitate to the further study of harmful algal blooms early-warning in this region.
Comparison of growth and nutrient uptake capacities of three dominant species of Qinhuangdao green tides
Hongbin Han, Ruobing Wen, Hui Wang, Sheng Zhao
2023, 42(4): 114-123.   doi: 10.1007/s13131-022-2100-7
[Abstract](141) [FullText HTML](45) [PDF 1401KB](12)
Since 2015, green tides have been blooming in offshore waters of Qinhuangdao, with serious impacts on the local ecological environment and tourism. Ulva australis, Bryopsis plumosa, and U. prolifera are the dominant species of Qinhuangdao green tides, following a sequential succession pattern. Ulva prolifera is the dominant species, with the highest biomass and the greatest influence on the local ecological environment. To study the reason of green tide dominant species succession and U. profilera became the dominant species with the largest biomass, we compared and analyzed the growth and nutrient uptake capacity of the three algae. The results showed that temperature significantly affects the growth of the three species. Within the temperature range of the experimental setup, the optimum temperature for the growth of U. australis, B. plumosa and U. profilera is 10℃, 15℃, and 20–25℃, respectively. Combined with the temperature variation trend during green tide bloom development, we believe that temperature is the key environmental factor for the succession of the dominant species. Ulva prolifera has a higher growth rate than U. australis and B. plumosa under the same nitrate, ammonium, and phosphate levels. Significant differences in the maximum absorption rate (Rmax) and Rmax/Ks (the relationship between uptake rate and substrate concentration) values indicated that U. prolifera had an apparent competitive advantage over U. australis and B. plumosa regarding nutrient uptake. Therefore, the strong growth and nutrient uptake capacities of U. prolifera might be the main reason for becoming the dominant species with the largest biomass in Qinhuangdao green tides.

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