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[Abstract](44) [FullText HTML](13)
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Qilianyu Islands coral reefs (QICR), located in the northeastern part of the South China Sea, has been affected by human activities and natural disturbance. To characterize the trophic structure, ecosystem properties and keystone species of this region, a food-web model for the QICR is developed using methods involving a mass-balance approach with Ecopath with Ecosim software. Trophic levels range from 1.00 for detritus and primary producers to 3.80 for chondrichthyes. The mean trophic transfer efficiency for the entire ecosystem is 13.15%, with 55% of total energy flow originating from primary producers. A mixed trophic impact analysis indicates that coral strongly impacts most components of this ecosystem. A comparison of our QICR model with that for other coral reef ecosystems suggests that the QICR ecosystem is immature and/or is degraded.
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The flux of settling particles in the ocean has been widely explored since 1980s due to its important role in biogenic elements cycling, especially in the transport of particulate organic carbon (POC) in the deep sea. However, research in the seamount area of the oligotrophic subtropical Northwest Pacific Ocean is lacking. In this work, two sediment traps were deployed at the foot and another two at the hillside of Niulang Guyot from August 2017 to July 2018. The magnitude and composition of particle fluxes were measured. The main factors influencing the spatial variations of the fluxes were evaluated. Our results indicated a low particulate flux from Niulang Guyot Area in the Northwest Pacific Ocean, reflecting low primary productivity of the oligotrophic ocean. The total mass flux (TMF) decreased from 2.57 g/(m2·a) to 0.56 g/(m2·a) with increasing depth from 600 m to 4 850 m. A clear seasonal pattern of TMF was observed, with higher flux in summer than that in winter. The peak flux of 26.52 mg/(m2·d) occurred in August at 600 m, while the lowest value of 0.07 mg/(m2·d) was shown in February at 4 850 m. The settling particles at the deep layers had similar biochemical composition, with calcium carbonate (CaCO3) accounting for up to 90%, followed by organic matter and opal, characteristics of Carbonate Ocean. The POC flux decreased more rapidly in the twilight layer because of faster decomposition, remineralization, and higher temperature. A small fraction of POC was transported into the deep ocean by biological pump. Particle fluxes were mainly controlled by the calcareous ballasts besides the primary productivity of the surface water. The advection may be another important factor affecting the flux in the seamount area. The combination of settled matters rich in foraminiferal tests with topography and currents may be the reason for regulating the local abundance of benthos on seamounts. Our results will fill in the knowledge gap of sedimentation flux, improve the understanding of ecosystem in Niulang Guyot area, and eventually provide data support for the optimization of regional ecological modeling.
[Abstract](53) [FullText HTML](11) [PDF 3380KB](0)
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The hydrographic and bio-optical properties of the Bering Sea shelf were analyzed based on in-situ measurements obtained during four cruises from 2007 to 2009. According to the temperature and salinity of the seawater, the spring water masses on the Bering Shelf were classified as the Alaskan Coast Water, Bering Sea Shelf Water, Anadyr Water, Spring Mixed Layer Water, Remnant Winter Water, and Winter Water, each of which had varying chlorophyll a concentrations. Among them, the highest chlorophyll a concentration occurred in the nutrient-rich Anadyr Water ((7.57±6.16) mg/m3 in spring). The spectrum-dependent diffuse attenuation coefficient (\begin{document}${K}_{\mathrm{d}}\left(\lambda \right)$\end{document}) of the water column for downwelling irradiance was also calculated, exhibiting a decrease at 412–555 nm and then an increase within the range of 0.17–0.48 m–1 in spring. Furthermore, a strong correlation between the chlorophyll a concentration and the attenuation coefficient was found at visible wavelengths on the Bering Shelf. Spatially, the chlorophyll a concentration was higher on the northern shelf ((5.18±3.78) mg/m3) than on the southern shelf ((3.64±2.51) mg/m3), which was consistent with the distribution of the attenuation coefficient. Seasonally, the consumption of nutrients by blooms resulted in minimum chlorophyll a concentration ((0.78±0.51) mg/m3) and attenuation coefficient values in summer. In terms of the vertical structure, both the attenuation coefficient and the chlorophyll a concentration tended to reach maximum values at the same depth, and the depth of the maximum values increased as the surface temperature increased in summer. Moreover, an empirical model was fitted with a power function based on the correlation between the chlorophyll a concentration and the attenuation coefficient at 412–555 nm. In addition, a spectral model was constructed according to the relationship between the attenuation coefficients at 490 nm and at other wavelengths, which provides a method for estimating the bio-optical properties of the Bering Shelf.
[Abstract](28) [FullText HTML](4)
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The abundance and health of scleractinian coral communities of Hormuz Island was investigated. For this purpose, we employed 20 m line intercept transects-12 in the intertidal zone and 15 subtidally to evaluate coral cover and community composition. The estimated dead coral coverage was 6.21%±0.81%, while live coral coverage was 16.93%±1.81%, considered as very poor. Totally, 12 genera were recorded, of which Porites with 11.9%±1.4% live cover was the dominant, while Goniopora had the least cover (0.07%±0.08%). Based on Mann-Whitney U-test, live coral coverage, dead coral coverage, algal coverage, cover of other benthic organisms and abiotic components showed significant univariate differences between zones (p<0.05). The Spearman correlation test between the abundance of biotic and abiotic components indicated significant negative correlation of live coral and sand with zoantharian and significant positive correlation of algae and other benthic organisms with rubble. The reef health indices used for the corals indicated that, in general, the environmental conditions were not suitable, which could be attributed to both natural and anthropogenic factors, the most important of which was zoantharian’ overgrowth on the scleractinian corals in this region.
[Abstract](38) [FullText HTML](7)
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The aim of this study was to evaluate the genetic parameters of the growth performance of Takifugu rubripes. Heritabilities and genetic correlations were estimated for body weight (BW), body length (BL), total length (TL), chest measurement (CM) and trunk length (TKL) of T. rubripes from measurements of progeny at 6 months and 12 months. The results showed that the heritability was 0.37 for BW6, 0.19 for BL6, 0.35 for TL6, 0.29 for CM6, 0.26 for TKL6, 0.36 for BW12, 0.26 for BL12, 0.25 for TL12, 0.31 for CM12 and 0.15 for TKL12. The range of genetic correlations estimated at 6 months was 0.025–0.725 and −0.002–0.706 at 12 months. The results indicated that genetic improvement for faster growth rate or increased body weight in cultured T. rubripes was effective. Based on selection theory, the selection strategy for traits with medium heritability is flexible. Considering that these growth traits do not reach the high level of heritability, family selection should be expected. Given positive genetic correlations among BW, BL, TL, CM, and TKL at 6 months, the five traits could be improved simultaneously through selective breeding. As there was high genetic correlation only between BW12, BL12 and TL12, and negative correlations between TKL12 and BL12 as well as between CM12 and TL12, and only BW, BL and TL at 12 months could be improved simultaneously.
[Abstract](54) [FullText HTML](13)
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Bathing beaches are usually the first to suffer disasters when tsunamis occur, owing to their proximity to the sea. Several large seismic fault zones are located off the coast of China. The impact of each tsunami scenario on Chinese bathing beaches is different. In this study, numerical models of the worst tsunami scenarios associated with seismic fault zones were considered to assess the tsunami hazard of bathing beaches in China. Numerical results show that tsunami waves from the Pacific Ocean could affect the East China Sea coast through gaps between the Ryukyu Trench Islands. The Zhejiang and Shanghai coasts would be threatened by a tsunami from Ryukyu Trench, and the coasts of Hainan and Guangdong provinces would be threatened by a tsunami from the Manila Trench. The tsunami hazard associated with the Philippine trench scenario needs particular attention. Owing to China’s offshore topography, the sequential order of tsunami arrival times to coastal provinces in several tsunami scenarios is almost the same. According to the tsunami hazard analysis results, Yalongwan Beach and eight other bathing beaches are at the highest hazard level. A high-resolution numerical calculation model was established to analyze the tsunami physical characteristics for the high-risk bathing beaches. To explore mitigating effects of a tsunami disaster, this study simulated tsunami propagation with the addition of seawalls. The experimental results show that the tsunami prevention seawalls constructed in an appropriate shallow water location have some effect on reducing tsunami hazard. Seawalls separated by a certain distance work even better. The analysis results can provide a scientific reference for subsequent preventive measures such as facility construction and evacuation.
[Abstract](42) [FullText HTML](8)
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Marine macroalgal sulfated fucose-containing polysaccharides, like fucoidan, have drawn significant attention due to their biotechnological potentials, such as anti-cancer, antioxidant, and anti-cholinesterase activities. The fucoidan derived from brown macroalgae Sargassum angustifolium species (FSA) was investigated for its cytotoxic effects and alterations in cell proliferation, and cell cycle-related gene expression in the present study occur on NB4 cell line. The results showed that FSA would induce p53, p21, pro-apoptotic genes and increase expression of the p15 gene as a cell arrest marker. Also, FSA inhibited the anti-apoptotic effect of the Bcl-2 gene and decreased dnmt-1 gene expression. FSA significantly exhibited potent 2, 2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity (p<0.05) with an IC50 value of 0.157 mg/mL and showed moderate anti-acetylcholinesterase activity with an IC50 value of 1.20 μg/mL. These results indicated the potential of FSA for the development of therapeutic or preventive agents of cancer and Alzheimer’s disease mainly through cytotoxic effect and AChE (acetylcholinesterase) inhibition as well as additional antioxidant capacities.
[Abstract](20) [FullText HTML](5)
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Studies in the northern South China Sea (SCS) basement remain important for understanding the evolution of the Southeast Asian continental margin. Due to a thick cover of sediments and scarce borehole penetration, little is known about the age and tectonic affinity of this basement. In this study, an integrated study of Zircon U-Pb geochronology, Hf isotopes, and whole-rock major and trace elements on seven basement granitoids from seven boreholes of Qiongdongnan Basin has been carried out. New zircon U-Pb results for these granitoids present Middle-Late Permian ((270.0±1.2) Ma; (253±3.4) Ma), Middle to Late Triassic ((246.2±3.4) Ma; (239.3±0.96) Ma; (237.9±0.99) Ma; (228.9±1.0) Ma) and Late Cretaceous ages ((120.6±0.6) Ma). New data from this study, in combination with the previous dataset, indicates that granitoid ages in northern SCS basement vary from 270 Ma to 70.5 Ma, with three age groups of 270–196 Ma, 162–142 Ma, and 137–71 Ma, respectively. Except for the Late Paleozoic-Mesozoic rocks in the basement of the northern SCS, a few old zircon grains with the age of (2708.1±17) Ma to (2166.6±19) Ma provide clues to the existence of the pre-Proterozoic components. The geochemical signatures indicate that the Middle Permian-Early Cretaceous granitoids from the Qiongdongnan Basin are I-type granites formed in a volcanic arc environment, which were probably related to the subduction of the Paleo-Pacific plate.
[Abstract](47) [FullText HTML](13) [PDF 988KB](6)
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The most important marine coastal ecosystem in the Chilean coast are kelp forests. This review is based on ecological studies regarding different aspects of subtidal kelp ecosystems along the Chilean coast. It highlights the most interesting findings in (1) biology of subtidal kelp in Chile, with particular reference to (2) habitats formed by kelp, and considered the successful examples and promising results in the (3) kelp as an industrial resource (Biotechnological approach of kelps and aquaculture). The impact caused by (4) El Niño-Southern Oscillation (ENSO) is discussed as an important climatic event that could help to forecast the future of the kelp ecosystem. In addition, this literature review outlines the knowledge gaps on subtidal kelp along the South East Pacific Coast of Chile, so that research can be strengthened in the future.
[Abstract](94) [FullText HTML](32) [PDF 9367KB](7)
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A wave-current-sediment coupled numerical model is employed to study the responses of suspended sediment transport in the wet season to changes in shoreline and bathymetry in the Zhujiang (Pearl) River Estuary (ZRE) from 1971 to 2012. It is shown that, during the wavy period, the large wave-induced bottom stress enhances sediment resuspension, resulting in an increase in the area of suspended sediment concentration (SSC) greater than 100 mg/L by 183.4%. On one hand, in spring tide, the change in shoreline reduces the area of SSC greater than 100 mg/L by 17.8% in the west shoal (WS) but increases the SSC, owing to the closer sediment source to the offshore and the stronger residual current at the Hengmeng (HEM) and Hongqili (HQL) outlets. The eastward Eulerian transport is enhanced in the WS and west channel (WC), resulting in a higher SSC there. The reclamation of Longxue Island (LXI) increases SSC on its east side and east shoal (ES) but decreases the SSC on its west and south sides. Moreover, in the WC, the estuarine turbidity maximum (ETM) is located near the saltwater wedge and moves southward, which is caused by the southward movement of the maximum longitudinal Eulerian transport. In neap tide, the changes are similar but relatively weaker. On the other hand, in spring tide, the change in bathymetry makes the SSC in the WS increase, and the area of SSC greater than 100 mg/L increases by 11.4% and expands eastward and southward, which is caused by the increases in wave-induced bottom stress and eastward Eulerian transport. On the east side of the WC, the eastward Eulerian transport decreases significantly, resulting in a smaller SSC in the middle shoal (MS). In addition, in the WC, the maximum SSC is reduced, which is caused by the smaller wave-induced bottom stress and a significant increase of 109.88% in southward Eulerian transport. The results in neap tide are similar to those in spring tide but with smaller changes, and the sediment transports northward in the WC owing to the northward Eulerian transport and vertical shear transport. This study may provide some references for marine ecological environment security and coastal management in the ZRE and other estuaries worldwide affected by strong human interventions.
[Abstract](32) [FullText HTML](6)
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Assessments of phytoplankton diversity in Sabah waters, North Borneo, have primarily relied on morphology-based identification, which has inherent biases and can be time-consuming. Next-Generation Sequencing (NGS) technology has been shown to be capable of overcoming several limitations of morphology-based methods. Samples were collected from Sepanggar Bay over the course of the year 2018 in different monsoon seasons. Morphology-based identification and NGS sequencing of the V8–V9 region of the 18S LSU rDNA were used to investigate the diversity of the phytoplankton community. Microscopy and NGS showed complementary results with more diatom taxa detected by microscopy whereas NGS detected smaller and rarer taxa. The harmful algal genera in the study site comprised of Skeletonema, Margalefidinium, Pyrodinium, Takayama, and Alexandrium as detected by NGS. This study showed that that an integrative approach of both morphological and molecular techniques could provide more comprehensive information about the phytoplankton community as the approach captured quantitative variability as well as the diversity of phytoplankton species.
[Abstract](27) [FullText HTML](8)
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The geochemical signatures of fifty-four rock samples and three supplementary drill stem test (DST) oils from the Yacheng-Sanya formations in the central Qiongdongnan Basin (CQB) were analysed. Reconstruction of the early Oligocene-early Miocene (36–16 Ma) palaeovegetation and source analyses of organic matter (OM) were conducted using aliphatic biomarkers in ancient sediments and DST oils. Both the interpreted aquatic and terrigenous OM contributed to the CQB source rocks (SRs) but have varying relative proportions. The four distribution patterns derived from n-alkanes, terpanes, and steranes are representative of four OM composition models of the Yacheng-Sanya SRs, including model A, model B, model C, and model D, which were classified based on the increasing contribution from terrigenous OM relative to aquatic OM. Some terrigenous higher plant-derived biomarkers, including oleanane, des-A-oleanane, C29 ααα 20R sterane, bicadinanes, the C19/(C19 + C23) tricyclic terpane ratio, and other n-alkane-derived ratios suggest that angiosperms had increased proportions in the palaeoflora from early Oligocene to early Miocene, and the bloom of terrigenous higher plants was observed during deposition of Upper Lingshui Formation to Lower Sanya Formation. These findings are consistent with the incremental total organic carbon and free hydrocarbons + potential hydrocarbons (S1 + S2) in the lower Lingshui-lower Sanya strata with a significant enrichment of OM in the E3l1-N1s2 shales. The maturity- and environment-sensitive aliphatic parameters of the CQB SRs and DST oils suggest that all the samples have predominantly reached their early oil-generation windows but have not exceeded the peak oil windows, except for some immature Sanya Formation shales. In addition, most of the OM in the analysed samples was characterised by mixed OM contributions under anoxic to sub-anoxic conditions. Furthermore, terrestrial-dominant SRs were interpreted to have developed mainly in the Lingshui-Sanya formations and were deposited in sub-oxic to oxic environments, compared to the anoxic to sub-anoxic conditions of the Yacheng Formation.
[Abstract](46) [FullText HTML](9)
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This study investigated the seasonal variation in the atmospheric response to oceanic mesoscale eddies in the North Pacific Subtropical Countercurrent (STCC) and its mechanism, based on satellite altimetric and reanalysis datasets. Although mesoscale eddy in the study area is more active in summer, the sea surface temperature (SST) anomaly associated with mesoscale eddies is more intense and dipolar in winter, which is largely due to the larger background SST gradient. Similarly, the impact of the oceanic eddy on sea surface wind speed and heat flux is strongest in winter, whereas its effect on precipitation rate is more significant in summer. The study revealed that the SST gradient in STCC could impact the atmosphere layer by up to 800 hPa (900 hPa) in boreal winter (summer) through the dominant vertical mixing mechanism. Moreover, the intensity of the SST gradient causes such seasonal variation in mesoscale air-sea coupling in the study region. In brief, a stronger (weaker) background SST gradient field in wintertime (summertime) leads to a larger (smaller) eddy-induced SST anomaly, thus differently impacting atmosphere instability and transitional kinetic energy flux over oceanic eddies, leading to seasonal variation in mesoscale air-sea coupling intensity.
[Abstract](39) [FullText HTML](7)
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High-resolution multi-beam/single-beam bathymetric data and seismic profiling data from the latest surveys are used to map and interpret the detailed seafloor geomorphology of the western region of the North Yellow Sea (NYS), China. The mapping area covers 156 410 km2, and incorporates a flat shelf plain, subaqueous accumulation shoals, tidal scouring troughs, and tidal sand ridge groups. Offshore areas with water depths <50 m in the western region of the NYS are mainly covered by thick, loose sediments, forming wide spread accumulation geomorphological features; these include the Liaodong Peninsula subaqueous accumulation system containing shoals and rugged scouring troughs, and the large mud wedge of the Shandong Peninsula. In the central part of the NYS, there is a relatively flat residual shelf plain with coarser sediment deposits. This flat shelf plain has a water depth >50 m and a thin layer of sediment, on which there is a large pockmark field caused by seafloor seepage. These geomorphological structures indicate that modern sedimentary processes are the main driving force controlling the sculpture of the current seafloor surface landform. Extensive strong tidal current systems and abundant sediment sources provide the critical external forces and essential conditions for the formation of seafloor geomorphology. The tectonic basement controls the macroscopic morphological shape of the NYS, but is reflected very little in the seafloor geomorphic elements. Our results provide a detailed seafloor geomorphological map of the western region of the NYS, an area that has not previously mapped and also provide a scientific framework for further research into offshore seafloor geomorphology, shelf sedimentary processes, and submarine engineering construction in this region.
[Abstract](16) [FullText HTML](4)
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The Clarion-Clipperton Zone (CCZ) hosts one of the largest known oceanic nodule fields worldwide and is regulated by the International Seabed Authority. A baseline assessment of diversity and distribution patterns is essential for reliable predictions of disturbed ecosystem response scenarios for sustained commercial activities in the future. In the present study, the spatial patterns and diversity of phytoplankton communities were analyzed along with upper ocean biogeochemistry, in the licensed China Ocean Mineral Resources R&D Association (COMRA) contract area and the surrounding western CCZ between August 21 and October 8, 2017. Results indicated this was a typical low-nutrient low-chlorophyll a (Chl a) environment, characterized by low levels of phytoplankton abundance and diversity. In total 112 species belonging to 4 phyla were recorded (>10 μm), with species counts including 82 diatoms, 27 dinoflagellates, 1 cyanobacteria and 2 chrysophyte. Dominant taxa in successive order of descending abundance and occurrence included Nizschia marina, Cyclotella stylorum, Dactyliosolen mediterraneus, Rhizosolenia setigera, Pseudo-nitzschia delicatissima, Thalassiothrix frauenfeldii, Synedra sp., Chaetoceros simplex and Pseudo-nitzschia circumphora. The depth-averaged abundance and Chl a concentrations were (265±233) cells/L and (0.27±0.30) μg/L, respectively. Diatoms accounted for 90.94% of the community with (241±223) cells/L, while dinoflagellates accounted for 5.67% and (15±13) cells/L. The distribution pattern exhibited the same trend as abundance, Chl a and species richness, showing subsurface maximum levels at around 100 m, with stations near 10°N having higher levels than in the north. Cluster analysis was performed in two assemblages, relating to geographic locations to the south and north of 12°N. The subsurface maximum of abundance, Chl a, species richness, dissolved oxygen and nitrite were generally corresponding to the presence of high salinity North Pacific Central Water at depths of 50-120 m. Higher availability of nitrate, phosphate and silicic acid in the subsurface may account for the shift in phytoplankton distribution, as shown by redundancy correspondence and spearman correlation analysis. Diel variation in an anchor station demonstrated prominent species succession without significant differences in oceanographic variables, among which diatoms succession resulted from the light limitation, while dinoflagellate diel variation mainly related to lateral transport of water masses. The observed patchiness in spatial phytoplankton distributional patterns was attributed to upper ocean environmental gradients in the CCZ. The baseline generated in this study could be analyzed using current conservation strategy programs associated with deep-sea mining.
[Abstract](17) [FullText HTML](3)
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Based upon cruise observations broadly covering the tropical North Pacific during July-November 2017, together with data obtained from the World Ocean Circulation Experiment Hydrographic Program, this study examined the distribution of dissolved inorganic nitrogen (DIN, nitrate (NO3-)+nitrite (\begin{document}${{\rm {NO}}_2^-}$\end{document})), dissolved inorganic phosphorus (DIP) and related N* (nitrogen-anomaly, N*=N−16P+2.9, where N and P are the concentrations of DIN (>1.0 μmol/L) and DIP (>0.1 μmol/L)), used as an index of N2 fixation, in the upper 1 000 m of the water column. Nutrient concentrations displayed distinct spatial variability in the upper ocean but became relatively constant at a depth of 1 000 m: they were high at low latitudes and in the eastern region, with an obvious nutricline at ~150 m (DIN, ~32.0 μmol/L; DIP, ~2.4 μmol/L) and then generally increased with depth; they decreased markedly (DIN, ~1.2 μmol/L; DIP, ~0.1 μmol/L; at ~150 m) at high latitudes and in the western region, where a nutricline was not apparent. The N* index showed significant meridional and zonal variation, with the most negative values located at low latitudes and in the eastern region (~10°N, ~170°−150°E), while becoming positive towards the northwest (the north of ~18°N, ~160°E westward). A N* concentration larger than 2 μmol/L often used as an indicator of N2[1]fixation, which was observed between 155°E and 165°E; N* values were 2.0 μmol/L to 6.0 μmol/L at ~15°−28°N, i.e., much higher than those in the southern sector (0−2.0 μmol/L at ~5°−10°N). Zonally, N* decreased gradually from west (−2.0 μmol/L to 4.0 μmol/L, ~145°−165°E) to east (−2.0 μmol/L to −8.0 μmol/L, ~155°W) along ~10°N, which was consistent with the distribution of Trichodesmium abundance and N2 fixation rates. Furthermore, since such region was also supplied with aeolian deposition, high N* was probably not only induced by N2 fixation but also influenced by iron and/or nitrogen deposition.
[Abstract](16) [FullText HTML](4)
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Resource exploitation in the Clarion-Clipperton Zone (CCZ) is of major research interest worldwide, but its influence on the environment is poorly understood, especially due to the lack of baseline values for metals in the surrounding sediment. This work aimed to establish the baseline values of 17 metals (Ba, Ca, K, Mg, Mn, Na, Ag, As, B, Cd, Co, Cr, Cu, Hg, Ni, Pb, and Zn) using normalization, the cumulative frequency curve method considering a total of 172 samples taken from 8 multitube cores and 1 box sediment core collected in the western CCZ during the COMRA-45 cruise campaign from August to September 2017. The baseline values of the evaluated metals were as follows: 1 932 mg/kg for Ba, 29 512 mg/kg for Ca, 18 150 mg/kg for K, 17 120 mg/kg for Mg, 6 747 mg/kg for Mn, 28 546 mg/kg for Na, 0.571 mg/kg for Ag, 5.00 mg/kg for As, 94.4 mg/kg for B, 0.626 mg/kg for Cd, 104 mg/kg for Co, 76.1 mg/kg for Cr, 370 mg/kg for Cu, 0.028 mg/kg for Hg, 190 mg/kg for Ni, 27.5 mg/kg for Pb and 156 mg/kg for Zn. Our findings would fill the baseline value gap in the study area and further improve accuracy of environmental impact assessments on the impact of resource exploitation.
[Abstract](28) [FullText HTML](8)
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Based on long-term tide gauge observations in the last 60 years, the temporal and spatial variation characteristics of sea level change along the coast of China are analyzed. The results indicate that the sea level along the coast of China has been rising at an increasing rate, with an estimated acceleration of 0.07 mm/a2. The rise rates were 2.4 mm/a, 3.4 mm/a and 3.9 mm/a during 1960–2020, 1980–2020 and 1993–2020, respectively. In the last 40 years, the coastal sea level has risen fastest in the South China Sea and slowest in the Yellow Sea. Seasonal sea levels all show an upward trend but rise faster in winter and spring and slower in autumn. Sea level change along the coast of China has significant periodic oscillations of quasi-2 a, 4 a, 7 a, 11 a, quasi-19 a and 30–50 a, among which the 2–3 a, 11 a, and 30–50 a signals are most remarkable, and the amplitude is approximately 1–2 cm. The coastal sea level in the most recent decade reached its highest value in the last 60 years. The decadal sea level from 2010 to 2019 was approximately 133 mm higher than the average of 1960–1969. Empirical orthogonal function (EOF) analysis indicates that China’s coastal sea level has been changing in a north-south anti-phase pattern, with Pingtan and Fujian as the demarcation areas. This difference was especially obvious during 1980–1983, 1995–1997 and 2011–2013. The coastal sea level was the highest in 2016, and this extreme sea level event was analyzed to be related mainly to the anomalous wind field and ENSO.
[Abstract](28) [FullText HTML](7)
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The productivity and health of seagrass depend on the combined inputs of nutrients from the water and sediments in which they grow and the microbiota with which they live intimately. However, little is known about the composition and diversity pattern of single-celled benthic eukaryotes in seagrass meadows. Here, we investigated how the structure and diversity of the benthic microeukaryotic community vary with respect to season, location, and seagrass colonization, by applying 18S rRNA gene amplicon sequencing for 96 surface sediment samples that were collected from three different seagrass habitats through four seasons. We found that benthic microeukaryotic communities associated with seagrass Zostera japonica exhibited remarkable spatial and seasonal variations, as well as differences between vegetated and unvegetated sediments. Diatoms and dinoflagellates predominated in the benthic microeukaryotic communities, but they were inversely correlated and displaced each other as the dominant microbial group in different seasons or habitats. Mucoromycota was more prevalent in vegetated sediments, whereas Lobulomycetales and Chytridiales had higher proportions in unvegetated sites. Total organic carbon and total organic nitrogen were the most important environmental factors in driving the microeukaryotic assemblages and diversity. Our study expands the available knowledge on the biogeographic distribution patterns and niche preferences for benthic microeukaryotes in seagrass systems.
[Abstract](31) [FullText HTML](7)
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In this paper, the intra-seasonal variability of the abyssal currents in the China Ocean Mineral Resources Association (COMRA) polymetallic nodule contact area, located in the western part of the Clarion and Clipperton Fraction Zone in the tropical East Pacific, is investigated using direct observations from subsurface mooring instruments as well as sea-surface height data and reanalysis products. Mooring observations were conducted from September 13, 2017 to August 15, 2018 in the COMRA contact area (10°N, 154°W). The results were as follows: (1) At depths below 200 m, the kinetic energy of intra-seasonal variability (20-100 d) accounts for more than 40% of the overall low-frequency variability, while the ratio reaches more than 50% below 2 000 m; (2) At depths below 200 m, currents show a synchronous oscillation with a characteristic time scale of 30 d, lasting from October to the following January; the energy of the 30-d oscillation increases with depth until the layer of approximately 4 616 m, and the maximum velocity is approximately 10 cm/s; (3) The 30-d oscillation of deep currents is correlated with the tropical instability waves in the upper ocean.
[Abstract](112) [FullText HTML](34) [PDF 2123KB](13)
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In the Xiangshan Bay at the east coast of China, coastal marine pollution is conspicuous and severe in recent years. As transport of the pollutants is closely related to the coastal circulation, there is a great practical significance to investigate the circulation in this area. In this work, the surface pattern and vertical profiles of Lagrangian residual velocity (LRV) were studied based on field observation data from the inner Xiangshan Bay. By tracking GPS-GPRS drifters’ trajectories, the surface LRV pattern is going out in the central deep trough and flowing inwards near the shoreside. Combined with data from two mooring stations, vertical profiles of LRV is flowing out at surface and flowing in at the bottom, consistent with the gravitational circulation induced by baroclinic effects at the estuary. However, according to the diagnostic analysis, the main mechanism driving the residual current is barotropic rather than baroclinic. The LRV equation is controlled by the tidally-averaged barotropic pressure gradient force, tidal body force and tidally-averaged turbulent stress, while the tidally-averaged baroclinic pressure gradient force is one order of magnitude less than other forces. Additionally, the tidally mean eddy viscosity coefficient which is used in the expression of tidally-averaged turbulent stress might be not adequate and requires further studies.
[Abstract](155) [FullText HTML](40) [PDF 2981KB](18)
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We report field measurements of vertical profiles of the turbulent diffusivity and temperature at different stations in the South China Sea (SCS). Our study shows that the measured turbulent diffusivity follows a power-law distribution with a varying exponent in water layers. Similar multiple-layer scaling regimes were also observed from the temperature fluctuations. Combining turbulent diffusivity and temperature fluctuations, the vertical structure of temperature was revealed. Furthermore, we discussed the temperature profiles in each layer. A constant function of a dimensionless temperature profile was found in water layers that have identical turbulence conditions. Our results reveal the multiple-layer structure of temperature in the SCS. This study contributes to the understanding of the vertical structure of multiple layers in the SCS and provides clues for exploring the physical mechanism for maintaining the temperature structure.
[Abstract](110) [FullText HTML](21) [PDF 3515KB](6)
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We introduced the Coupled Model Intercomparison Project Phase 6 (CMIP6) Ocean Model Intercomparison Project CORE2-forced (OMIP-1) experiment by using the First Institute of Oceanography Earth System Model version 2.0 (FIO-ESM v2.0), and comprehensively evaluated the simulation results. Unlike other OMIP models, FIO-ESM v2.0 includes a coupled ocean surface wave component model that takes into account non-breaking surface wave-induced vertical mixing in the ocean and effect of surface wave Stokes drift on air-sea momentum and heat fluxes in the climate system. A sub-layer sea surface temperature (SST) diurnal cycle parameterization was also employed to take into account effect of SST diurnal cycle on air-sea heat ﬂuxes to improve simulations of air-sea interactions. Evaluations show that mean values and long-term trends of significant wave height were adequately reproduced in the FIO-ESM v2.0 OMIP-1 simulations, and there is a reasonable fit between the SST diurnal cycle obtained from in situ observations and that parameterized by FIO-ESM v2.0. Evaluations of model drift, temperature, salinity, mixed layer depth, and the Atlantic Meridional Overturning Circulation show that the model performs well in the FIO-ESM v2.0 OMIP-1 simulation. However, the summer sea ice extent of the Arctic and Antarctic is underestimated.
[Abstract](41) [FullText HTML](7) [PDF 30740KB](5)
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Internal solitary waves (ISWs) are common mesoscale dynamic processes in the ocean that are spread throughout the world’s oceans. The South China Sea (SCS), Western Pacific (WPAC) and Indian Ocean (EIND) (SCS-WPAC-EIND) are areas where ISWs frequently occur. In particular, in the northern part of the South China Sea, Sulu Sea, Celebes Sea, Andaman Sea, Lombok Strait and northeastern part of Taiwan Island, ISWs exist almost year-round. Remote sensing is an important technique to carry out investigations and research on ISWs on a large scale. In particular, optical sensors represented by the Moderate Resolution Imaging Spectroradiometer (MODIS) can observe ISWs for a long time and on a large scale, while SAR sensors such as Sentinel-1 A/B can compensate for the deficiencies in optical sensors and comprehensively observe ISWs. Based on many years of remote sensing surveys of ISWs, this paper uses MODIS and Sentinel-1 satellite remote sensing images of more than 70 000 scenes from 2010 to 2020 to carry out survey studies of ISWs in the SCS-WPAC-EIND. The survey systematically gives the temporal and spatial distribution characteristics of ISWs in the SCS-WPAC-EIND and focuses on the analysis of the ISW characteristics in main areas in the SCS-WPAC-EIND, thereby providing basic data for further research on ISWs.
[Abstract](64) [FullText HTML](17) [PDF 1819KB](2)
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The surroundings of the Bay of Bengal (BoB) suffer a lot from the extreme rainfall events during Indian summer monsoon (ISM). Previous studies have proved that the sea-air interaction is an important factor for the monsoonal precipitation. Using the 6th Coupled Modol Inter-comparison Project (CMIP6) models, this study examined the biases of surface heat flux, which is the main connection between atmosphere and ocean. Results show that although CMIP6 have a better simulation of intraseasonal sea surface temperature (SST) anomalies over BoB than the previous ones, the “atmospheric blockage” still delays the response of latent heat flux to the oceanic forcing. Specifically, during the increment of positive latent heat flux in CMIP6, the negative contribution from wind effects covers most of the positive contribution from humidity effects, due to the underestimate of humidity effects. Further diagnostic analysis denote that the surface air humidity has a quarter of a phase ahead of warm SST in observation, but gets wet along with the warm SST accordingly in most CMIP6 models. As a result, the simulated transfer of intraseasonal moisture flux is hindered between ocean and atmosphere. Therefore, as a bridge between both sides, the atmospheric boundary layer is essential for a better sea-air coupled simulation, especially when the atmospheric and the oceanic variabilities involved in a climate model becomes increasingly sophisticated. The surface air humidity and boundary layer processes require more attention as well as better simulations.
[Abstract](65) [FullText HTML](21)
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Polycyclic aromatic hydrocarbons (PAHs) pollution, particularly in coastal environments, is a global concern. In this study, the biomonitoring and ranking effects of PAHs in the rockfish Sebastiscus marmoratus were determined in the Maowei Sea, China. The results showed that the concentrations of the 16 priority PAHs detected in the surface seawater were moderate compared with those in other coastal areas worldwide, and the possible sources were rapid industrialization and urbanization combined with atmospheric deposition and runoff. Nested analysis of variance (ANOVA) suggested significant differences in the hepatic ethoxyresorufin-O-deethylase (EROD) activities and phenanthrene-derived metabolites in bile between the port area and the oyster farming area. The fish expert system (FES) was applied to evaluate the biological effects of PAHs on fish. The FES data demonstrated that the biological effect levels of site S1 (level III, medium stress) were higher than those of the other sampling sites (level II, low stress).
[Abstract](36) [FullText HTML](10)
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Pituitary gland, or pituitary for short, is characteristic of all vertebrates. As a “master gland” controlling a multitude of important functions in the body, its evolutionary origin has been an object of investigations of evolutionary biology for two centuries. Previous morphological, ultrastructural and immunohistochemical studies suggested the homology of the Hatschek’s pit of amphioxus and vertebrate pituitary. Developmental genetics study showed that the development of Hatschek’s pit and vertebrate pituitary is both subject to regulation by the common genes such as Pit1, Lhx3 and BMP3b. Our recent studies demonstrated that the Hatschek’s pit is able to secrete GH-like hormone and TSH-like hormone that both play functions similar to vertebrate GH and TSH. We thus think that the emergence of Hatschek’s pit represents one of important events during endocrine network evolution, which laid a foundation for the subsequent formation of a hypothalamic-pituitary system in vertebrates.
[Abstract](50) [FullText HTML](14)
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The brain plays a critical role in controlling reproduction through the hypothalamus-pituitary-gonadal (HPG) axis in vertebrates. Turbot (Scophthalmus maximus) has become an economically important marine fish in Europe and North China. Previous research investigating turbot reproduction has focused on the role of the HPG axis in regulating egg and sperm production. However, the morphology and histology of the organs in the HPG axis have not been studied. In this study, we investigated the morphology and histology of brains in female and male turbot at different stages of gonadal development. The results showed that the brains of both female and male turbot were composed of seven parts that are typical of advanced teleosts; the telencephalon, diencephalon, cerebellum, hypothalamus, pituitary gland, myelencephalon, and olfactory bulbs. The telencephalon was well-developed and contained five distinct lobes, with the contiguous diencephalon at the caudal portion. The torus longitudinales and rostral torus semicircularis of the mesencephalon flattened along the dorsal surface, and the rostral corpus cerebellum was located in the dorsal portion. The actual total brain volume in mature males was significantly greater (p<0.05) than that of females with gonadal development. Notably, the pituitary volume in male turbot significantly increased (p<0.05) from immature to mature stage, but this difference did not occur in females. The data together illustrate a distinct sex difference in the turbot brain during gonadal development, providing insight into their HPG axes.
[Abstract](47) [FullText HTML](14)
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With the decline in fish resources worldwide, the ecological dominance and economic importance of crustaceans have obviously increased. Among crustacean species, mantis shrimp are increasingly dominant in many coastal waters of the world. In China, Oratosquilla oratoria is the most widely distributed and productive species of mantis shrimp, and its relative resource density is the highest in the Bohai Sea. In this study, we analysed the long-term and monthly population characteristics of O. oratoria in the Bohai Sea, including its relative resource density, body size and spatial distribution. The results showed that the relative resource density of O. oratoria in the Bohai Sea increased from 3.59 kg/h in 1982 to 14.48 kg/h in 2018, and the percentage of this species that serves as a fishery resource increased from 4.22% in 1982 to 35.27% in 2018, based on the mean relative resource density in May and August. The relative resource density of O. oratoria in the fishing moratorium season from May to August was significantly higher than that in the other months of fishing season, and the relative resource density decreased rapidly after the fishing moratorium ended. The relative resource density of O. oratoria was the highest in summer (August), followed by in autumn (October) and spring (May), and it was the lowest in winter (January). The relative resource density of O. oratoria in the western Bohai Sea was higher than that in the eastern Bohai Sea. The mean body weight of O. oratoria in the Bohai Sea decreased from 21.95 g in 1982 to 14.34 g in 2018, based on the mean body weight in May and August. The body size of O. oratoria in the fishing moratorium season was significantly higher than that in the fishing season, and the body size decreased rapidly after the fishing moratorium ended. Overall, in the context of declining resources of most fishery species, the relative resource density of O. oratoria increased due to its hardiness and adaptability, and its body size decreased under intensive fishing over the past 30 years. The fishing moratorium system had a great influence on the population dynamics of O. oratoria in terms of the relative resource density and body size in the Bohai Sea.
[Abstract](38) [FullText HTML](13)
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Although the adverse impacts of ocean acidification (OA) on marine calcifiers have been investigated extensively, the anti-stress capabilities regulated by increased light availability are unclear. Herein, the interactive effects of three light levels (30 μmol photons/(m2·s), 150 μmol photons/(m2·s), and 240 μmol photons/(m2·s) combined with two pCO2 concentrations (400 and 1400 ppmv) on the physiological acclimation of the calcifying macroalga Halimeda opuntia were investigated using a pCO2-light coupling experiment. The OA negatively influenced algal growth, calcification, photosynthesis, and other physiological performances in H. opuntia. The relative growth rate under elevated pCO2 conditions significantly declined by 13.14%−41.29%, whereas net calcification rates decreased by nearly three-fold under OA conditions. Notably, increased light availability enhanced stress resistance through the accumulation of soluble organic molecules, especially soluble carbohydrate, soluble protein, and free amino acids, and in combination with metabolic enzyme-driven activities, OA stress was alleviated. The carotenoid content under low light conditions increased markedly, and the rapid light curve of the relative electron transport rate was enhanced significantly by increasing light intensities, indicating that this new organization of the photosynthetic machinery in H. opuntia accommodated light variations and elevated pCO2 conditions. Thus, the enhanced metabolic performance of the calcifying macroalga H. opuntia mitigated OA-related stress.
[Abstract](30) [FullText HTML](6)
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Some deep-sea microbes may incorporate inorganic carbon to reduce CO2 emission to upper layer and atmosphere. How the microbial inhabitants can be affected under addition of bicarbonate has not been studied using in situ fixed and lysed samples. In this study, we cultivated 40 L natural bottom water at ~1 000 m depth with a final concentration of 0.1 mmol/L bicarbonate for 40 min and applied multiple in situ nucleic acids collection (MISNAC) apparatus for nucleic acids extraction from the cultivation. Our classification result of the cultivation sample showed a distinct microbial community structure, compared with the samples obtained by Niskin bottle and six working units of MISNAC. Except for notable enrichment of Alteromonas, we detected prevalence of Asprobacter, Ilumatobacter and Saccharimonadales in the cultivation. Deep-sea lineages of Euryarchaeota, SAR406, SAR202 and SAR324 were almost completely absent from the cultivation and Niskin samples. This study revealed the dominant microbes affected by bicarbonate addition and Niskin sampling, which suggested rapid responses of deep-sea microbes to the environmental changes.
[Abstract](40) [FullText HTML](9)
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While prokaryotes play key roles in nutrient cycling and energy flow during Phaeocystis globosa blooms, the information on the spatial and diel temporal distribution of the prokaryotic community during Phaeocystis blooms remains scarce. In January 2019, we used high-throughput sequencing of the 16S rRNA gene to explore the spatial and diel variations of particle-attached (PA) and free-living (FL) prokaryotic communities during the blooming phase of P. globosa in Beibu Gulf, Guangxi province, China. The results suggested a significant spatial variation pattern in the horizontal distribution of prokaryotic communities, while there was no significant difference in the vertical direction. Both spatial distance and environmental variables shaped the horizontal distribution of the prokaryotic community structure, while environmental variables, particularly the abundance of P. globosa colony and Chl a, showed more significant influence and were closely related to the structure and variation of the prokaryotic community. Strong vertical mixing of the water column disrupted the vertical structure heterogeneity of the prokaryotic community in winter. There were significant differences in the diel samples of PA prokaryotic communities, but not in the FL prokaryotic communities. Nitrate and ammonium and the abundance of P. globosa colony were the key environmental variables impacting the diel variations of prokaryotic communities over the sampling period. The present study provided valuable information to depict the spatial-temporal variations of the microbial community and its association with environmental parameters during P. globosa bloom in the tropical gulf.
[Abstract](84) [FullText HTML](28)
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We report for the first time the presence of local populations of the starfish Odontaster penicillatus in the regions of Atacama and Antofagasta, Chile. This finding indicates an extension of the distribution limit of 500 km with respect to the last observation made in 2007 in Isla Grande de Atacama. A total of 121 specimens of O. penicillatus were recorded at depths of between 8 m and 24 m. They were associated with rocky substrate and with different species of barnacles, sponges and bryozoans. The presence of O. penicillatus expands the knowledge of the benthic biodiversity of the region, and the development of studies on its ecological importance will be promoted.
[Abstract](75) [FullText HTML](17) [PDF 3177KB](5)
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The Arctic Oscillation (AO) has important effects on the sea ice change in terms of the dynamic and thermodynamic processes. However, while the dynamic processes of AO have been widely explored, the thermodynamic processes of AO need to be further discussed. In this paper, we use the fifth state-of-the-art reanalysis at European Centre for Medium-Range Weather Forecasts (ERA5) from 1979 to 2020 to investigate the relationship between AO and the surface springtime longwave (LW) cloud radiative forcing (CRF), summertime shortwave (SW) CRF in the Arctic region (65°−90°N). In addition, the contribution of CRF induced by AO to the sea ice change is also discussed. Results indicate that the positive (negative) anomalies of springtime LW CRF and summertime SW CRF are generally detected over the Arctic Ocean during the enhanced positive (negative) AO phase in spring and summer, respectively. Meanwhile, while the LW (SW) CRF generally has a positive correlation with AO index (AOI) in spring (summer) over the entire Arctic Ocean, this correlation is statistically significant over 70°−85°N and 120°W−90°E (i.e., region of interest (ROI)) in both seasons. Moreover, the response of CRF to the atmospheric conditions varies in spring and summer. We also find that the positive springtime (summertime) AOI tends to decrease (increase) the sea ice in September, and this phenomenon is especially prominent over the ROI. The sensitivity study among sea ice extent, CRF and AOI further reveals that decreases (increases) in September sea ice over the ROI are partly attributed to the springtime LW (summertime SW) CRF during the positive AOI. The present study provides a new pattern of AO affecting sea ice change via cloud radiative effects, which might benefit the sea ice forecast improvement.
[Abstract](50) [FullText HTML](13)
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Texture-based visualization method is a common method in the visualization of vector field data. Aiming at adding color mapping to the texture of ocean vector field and solving the ambiguity of vector direction in texture image, a new color texture enhancement algorithm based on the Line Integral Convolution (LIC) for the vector field data is proposed, which combines the HSV color mapping and cumulative distribution function calculation of vector field data. This algorithm can be summarized as follows: firstly, the vector field data is convoluted twice by line integration to get the gray texture image. Secondly, the method of mapping vector data to each component of the HSV color space is established. And then, the vector field data is mapped into HSV color space and converted from HSV to RGB values to get the color image. Thirdly, the cumulative distribution function of the RGB color components of the gray texture image and the color image is constructed to enhance the gray texture and RGB color values. Finally, both the gray texture image and the color image are fused to get the color texture. The experimental results show that the proposed LIC color texture enhancement algorithm is capable of generating a better display of vector field data. Furthermore, the ambiguity of vector direction in the texture images is solved and the direction information of the vector field is expressed more accurately.
[Abstract](72) [FullText HTML](22) [PDF 2008KB](4)
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The monsoon intraseasonal oscillation (MISO) is the dominant variability over the Indian Ocean during the Indian summer monsoon (ISM) season and is characterized by pronounced northward propagation. Previous studies have shown that general circulation models (GCMs) still have difficulty in simulating the northward-propagating MISO, and that the role of air-sea interaction in MISO is unclear. In this study, 14 atmosphere-ocean coupled GCMs (CGCMs) and the corresponding atmosphere-only GCMs (AGCMs) are selected from Phase 6 of the Coupled Model Intercomparison Project (CMIP6) to assess their performance in reproducing MISO and the associated vortex tilting mechanism. The results show that both CGCMs and AGCMs are able to well simulate the significant relationship between MISO and vortex tilting. However, 80% of CGCMs show better simulation skills for MISO than AGCMs in CMIP6. In AGCMs, the poor model fidelity in MISO is due to the failure simulation of vortex tilting. Moreover, it is found that failure to simulate the downward motion to the north of convection is responsible for the poor simulation of vortex tilting in AGCMs. In addition, it is observed that there is a significant relationship between the simulated sea surface temperature gradient and simulated vertical velocity shear in the meridional direction. These findings indicate that air-sea interaction may play a vital role in simulating vertical motions in tilting and MISO processes. This work offers us a specific target to improve the MISO simulation and further studies are needed to elucidate the physical processes of this air-sea interaction coupling with vortex tilting.
[Abstract](59) [FullText HTML](11)
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Compared to single-polarization synthetic aperture radar (SAR) data, fully polarimetric SAR data can provide more detailed information of the sea surface, which is important for applications such as shallow sea topography detection. The Gaofen-3 satellite provides abundant polarimetric SAR data for ocean research. In this paper, a shallow sea topography detection method was proposed based on fully polarimetric Gaofen-3 SAR data. This method considers swell patterns and only requires SAR data and little prior knowledge of the water depth to detect shallow sea topography. Wave tracking was performed based on preprocessed fully polarimetric SAR data, and the water depth was then calculated considering the wave parameters and the linear dispersion relationships. In this paper, four study areas were selected for experiments, and the experimental results indicated that the polarimetric scattering parameter α (alpha) had higher detection accuracy than quad-polarization images. The mean relative errors were 14.52%, 10.30%, 12.56%, and 12.90%, respectively, in the four study areas. In addition, this paper also analyzed the detection ability of this model for different topographies, and the experiments revealed that the topography could be well recognized when the topography gradient is small, the topography gradient direction is close to the wave propagation direction, and the isobath line is regular.
[Abstract](84) [FullText HTML](25) [PDF 4835KB](17)
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The wave-induced setup and circulation in a two dimensional horizontal (2DH) reef-lagoon-channel system is investigated by a non-hydrostatic model. The simulated results agree well with observations from the laboratory experiments, revealing that the model is valid in simulating wave transformation and currents over reefs. The effects of incident wave height, period, and reef flat water depth on the mean sea level and wave-driven currents are examined. Results show that the distributions of mean sea level and current velocities on the reef flat adjacent to the channel vary significantly from those in the area close to the side walls. From the wave averaged current field, an obvious alongshore flux flowing from the reef flat to the channel is captured. The flux from the reef flat composes the second source of the offshore rip current, while the first source is from the lagoon. A detailed momentum balance analysis shows that the alongshore current is mainly induced by the pressure gradient between the reef flat and the channel. In the lagoon, the momentum balances are between the pressure and radiation stress gradient, which drives flow towards the channel. Along the channel, the offshore current is mainly driven by the pressure gradient.
[Abstract](74) [FullText HTML](19) [PDF 2407KB](12)
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The near-inertial waves (NIWs) are important for energy cascade in the ocean. They are usually significantly reinforced by strong winds, such as typhoon. Due to relatively coarse resolutions in contemporary climate models, NIWs and associated ocean mixing need to be parameterized. In this study, a parameterization for NIWs proposed by Jochum in 2013 (J13 scheme), which has been widely used, is compared with the observations in the South China Sea, and the observations are treated as model outputs. Under normal conditions, the J13 scheme performs well. However, there are noticeable discrepancies between the J13 scheme and observations during typhoon. During Typhoon Kalmaegi in 2014, the inferred value of the boundary layer is deeper in the J13 scheme due to the weak near-inertial velocity shear in the vertical. After typhoon, the spreading of NIWs beneath the upper boundary layer is much faster than the theoretical prediction of inertial gravity waves, and this fast process is not rendered well by the J13 scheme. In addition, below the boundary layer, NIWs and associated diapycnal mixing last longer than the direct impacts of typhoon on the sea surface. Since the energy dissipation and diapycnal mixing below the boundary layer are bounded to the surface winds in the J13 scheme, the prolonged influences of typhoon via NIWs in the ocean interior are missing in this scheme. Based on current examination, modifications to the J13 scheme are proposed, and the modified version can reduce the discrepancies in the temporal and vertical structures of diapycnal mixing.
[Abstract](38) [FullText HTML](6)
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The Mohn Ridge separates the Greenland Sea and the Lofoten Basin. Previous studies identified the export across the Mohn Ridge (EMR) from the Greenland Basin into the Lofoten Basin using water mass analysis and the tracer diffusion method, but there is still lack of direct current measurements. A surface mooring with four current meters was deployed on the Mohn Ridge from June 5 to June 18 in 2015, when three cyclones passed in the adjacent area. In the absence of cyclones, the flow on the Mohn Ridge was northeastward, parallel to the ridge. When cyclones appeared, the EMR occurred to transport Greenland Sea water into the Lofoten Basin. The probable mechanism is the sea level height variation caused by the perturbation of the low pressure of cyclones, which yields an outward pressure gradient force to drive the outflow. Our results suggest that the outflow is intermittent and only happens during cyclone activities. The annual mean volume flux of EMR was roughly estimated by the limited data, which is about 3.8×106 m3/s, a little bit smaller than the estimation based on volume conservation. The results indicate that the contribution of the cyclonic storms to EMR is a greatly important mechanism that potentially influences the global thermohaline circulation through the Greenland-Scotland Ridge overflow.
[Abstract](74) [FullText HTML](16)
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Hypoxia is increasingly reported off the Changjiang River Estuary with the confluence of multiple high volume nutrient sources. The Regional Ocean Modeling System coupled with a biological model was used to analyze the effect of different nutrient sources on the development of hypoxia off the Changjiang River Estuary. By comparing to observed data, our model suitably captured the regional dynamics of chlorophyll a, dissolved oxygen, and nutrient concentration. A series of sensitivity experiments were conducted to investigate the hypoxia response to the various nutrient sources, such as loading from the Changjiang River, Kuroshio and Taiwan Warm Current. Our model results indicated that nutrients from different sources significantly influenced the hypoxia off the Changjiang River Estuary, and it was mostly affected by nutrients sourced from the Kuroshio. The nutrients input from the Changjiang River had larger impacts on the hypoxia in the north of 30°N than that in the south of 30°N. The nutrients sourced from the Taiwan Strait had a least influence on the hypoxia off the Changjiang River Estuary.
[Abstract](48) [FullText HTML](11)
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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.
[Abstract](64) [FullText HTML](10)
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Ocean eddies produce strong vertical heat flux (VHF) in the upper ocean, exerting profound influences on the climate and ecosystem. Currently, mooring array provides a standard way to estimate the eddy-induced VHF (EVHF) based on the adiabatic potential density equation. Apart from the validity of adiabatic assumption, it remains unclear to what extent the estimated EVHF at a single location within a limited time period is representative of its climatological mean value. In this study, we analyzed the above issue by systematically evaluating the variability of EVHF simulated by a 1-km ocean model configured over the Kuroshio Extension.It is found that the EVHF at a single location exhibits pronounced variability. Even averaged over one year that is comparable to the current maintenance capacity of mooring array, the EVHF still deviates significantly from its climatological mean value. For more than 49% of locations in our computational domain (31°–40°N, 149 °–166°E), the discrepancy between the one-year mean EVHF and its climatological mean value at the peaking depth is larger than the climatological mean itself. The mesoscale eddies play a dominant role in the variability of EVHF but contribute little to the climatological mean EVHF; the opposite is true for submesoscale eddies. Our findings indicate that nested mooring array allowing for isolating the effects of submesoscale eddies will be useful to obtain climatological mean EVHF.
[Abstract](248) [FullText HTML](84) [PDF 4624KB](37)
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Mesoscale eddies play vital roles in ocean processes. Although previous studies focused on eddy surface features and individual three-dimensional (3D) eddy cases in the northwestern Pacific Ocean, the analysis of unique eddy 3D regional characteristics is still lacking. A 3D eddy detection scheme is applied to 9 years (2000–2008) of eddy-resolving Regional Ocean Modeling System (ROMS) output to obtain a 3D eddy dataset from the surface to a depth of 1 000 m in the northwestern Pacific Ocean (15°–35°N and 120°–145°E). The 3D characteristics of mesoscale eddies are analyzed in two regions, namely, Box1 (Subtropical Countercurrent, 15°–25°N and 120°–145°E) and Box2 (Southern Kuroshio Extension, 25°–35°N and 120°–145°E). In Box1, the current is characterized by strong vertical shear and weak horizontal shear. In Box2, the current is characterized by the strong Kuroshio, topographic effect, and the westward propagation of Rossby waves. The results indicate the importance of baroclinic instability in Box1, whereas in Box2, both the barotropic and baroclinic instability are important. Moreover, the mesoscale eddies’ properties in Box1 and Box2 are distinct. The eddies in Box1 have larger number and radius but a shorter lifetime. By contrast, Box2 has fewer eddies, which have smaller radius but longer lifetime. Vertically, more eddies are detected at the subsurface than at the surface in both regions; the depth of 650 m is the turning point in Box1. Above this depth, the number of cyclonic eddy (CE)s is larger than that of anticyclonic eddy (AE)s. In Box2, the number of CEs is dominant vertically. Eddy kinetic energy (EKE) and mean normalized relative vorticity in Box2 are significantly higher than those in Box1. With increasing depth, the attenuation trend of EKE and relative vorticity of Box1 become greater than those of Box2. Furthermore, the upper ocean (about 300 m in depth) contains 68.6% of the eddies (instantaneous eddy). Only 16.6% of the eddies extend to 1 000 m. In addition, more than 87% of the eddies are bowl-shaped eddies in the two regions. Only about 3% are cone-shaped eddies. With increasing depth of the eddies, the proportion of bowl-shaped eddies gradually decreases. Conversely, the cone- and lens-shaped eddies are equal in number at 700–1 000 m, accounting for about 30% each. Studying the 3D characteristics of eddies in two different regions of the northwestern Pacific Ocean is an important stepping stone for discussing the different eddy generation mechanisms.
[Abstract](305) [FullText HTML](73)
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Three long-term fixed acoustic Doppler current profilers (ADCPs) were first used for investigating the vertical structure of tidal currents in Xuliujing Section of Changjiang River Estuary. Moreover, three different periods (spring, summer and fall) were also considered for investigating seasonal variations. The semi-diurnal tides were the most energetic, with along-channel speed of up to 80 cm/s for M2 constituent, which dominates at all stations with percent energy up to 65%–75% during seasons. The shape of tidal ellipses of the most energetic semi-diurnal constituent M2 showed obvious polarization of the flow paralleling to the riverbank, with the minor semi-axis being generally general less than 20% of the major one. The maximum velocity of mean current is appeared in top layers at all the three stations, and the velocity decreased with the depth. The seasonal variations of direction are also observed, which is probably caused by complex local topography since the erosion and deposition in riverbed. Observed vertical variation of four parameters of M2 ellipses, agreed well with the optimally fit frictional solutions in top and middle layers. However, there was an obvious difference between frictional model and observed data in the lower water column. Discrepancies are probably on account of stratification, which strengthens in summer and fall due to the freshening influence of the Changjiang River Estuary outflow.
[Abstract](333) [FullText HTML](94)
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Protease-producing bacteria play key roles in the degradation of organic nitrogen materials in marine sediments. However, their diversity, production of proteases and other extracellular enzymes, even in situ ecological functions remain largely unknown. In this study, we investigated the diversity of cultivable extracellular protease-producing bacteria in the sediments of the Bohai Bay. A total of 109 bacterial isolates were obtained from the sediments of 7 stations. The abundance of cultivable protease-producing bacteria was about 104 CFU/g of sediment in all the samples. Phylogenetic analysis based on 16S rRNA gene sequences classified all the isolates into 14 genera from phyla Proteobacteria, Firmicutes, Bacteroidetes and Actinobacteria, with Pseudoalteromonas (63/109, 57.8%), Bacillus (9/109, 8.2%), Sulfitobacter (8/109, 7.3%) and Salegentibacter (6/109, 5.5%) as the dominant taxa. Enzymatic inhibition tests indicated that all the tested isolates produced serine and/or metalloprotease, with only a small proportion producing cysteine and/or aspartic proteases. Several extracellular enzyme activities, including alginase, lipase, amylase and cellulose, and nitrate reduction were also detected for strains with higher protease activities. According the results, the protease-producing bacteria could also be participate in many biogeochemical processes in marine sediments. Our study broadened understanding and knowledge on the potential ecological functions of protease-producing bacteria in marine sediments.
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2022, 41(9).
[Abstract](27) [PDF 2349KB](8)
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2022, 41(9): 1-2.
[Abstract](22) [FullText HTML](7) [PDF 66KB](3)
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2022, 41(9): 1-18.   doi: 10.1007/s13131-022-1995-3
[Abstract](166) [FullText HTML](61) [PDF 3178KB](26)
Abstract:
The role of wave breaking (WB) in the ocean dynamics in the Bohai Sea, China under typhoon condition is systematically investigated utilizing a coupled wave-current model. The influences of WB on ocean dynamics and processes (mixing coefficient, temperature, mixed layer depth, and current) during the entire typhoon period (including the pre-typhoon, during-typhoon and after-typhoon stages) are comprehensively detected and discussed. Experimental results show that WB greatly enhances the turbulent mixing at about top 10 m depth under typhoon condition, the increase can be up to 10 times that of the normal weather. At the same time, WB generally strengthens the sea surface cooling by ~1.2°C at the during-typhoon stage, about 3 times that in normal weather. The mixed layer depth, is rapidly increased by ~1.6–3.6 m during typhoon due to WB, particularly, the deepening is stronger in the region from 120.5°E to 121.0°E on account of close to the typhoon eye. In addition, WB renders the current speed more uniformly within the entire depth in the Bohai Sea, the change in speed is ~0.2 m/s, whereas the alternation in current vector is generally opposite to the wind direction except for the typhoon eye region, reflecting that WB has an inhibitory effect on the typhoon-forced current change. The effects of WB on vertical mixing coefficient response to the typhoon rapidly, while the impacts of WB on temperature, and mixed layer depth present hysteretic responses to typhoon. Finally, the mechanisms and distribution characteristics of WB-induced mixing and tidal mixing are compared under typhoon condition.
2022, 41(9): 19-37.   doi: 10.1007/s13131-022-1998-0
[Abstract](199) [FullText HTML](72) [PDF 7743KB](39)
Abstract:
Variations in incoming shortwave radiation influence the net surface heat flux, contributing to the formation of a temperature inversion. The effects of shortwave radiation on the temperature inversions in the Bay of Bengal and eastern equatorial Indian Ocean have never been investigated. Thus, a high-resolution (horizontal resolution of 0.07°×0.07° with 50 vertical layers) Regional Ocean Modeling System (ROMS) model is utilized to quantify the contributions of shortwave radiation to the temperature inversions in the study domain. Analyses of the mixed layer heat and salt budgets are performed, and different model simulations are compared. The model results suggest that a 30% change in shortwave radiation can change approximately 3% of the temperature inversion area in the Bay of Bengal. Low shortwave radiation reduces the net surface heat flux and cools the mixed layer substantially; it also reduces the evaporation rate, causing less evaporative water vapor losses from the ocean than the typical situation, and ultimately enhances haline stratification. Thus, the rudimentary outcome of this research is that a decrease in shortwave radiation produces more temperature inversion in the study region, which is primarily driven by the net surface cooling and supported by the intensive haline stratification. Moreover, low shortwave radiation eventually intensifies the temperature inversion layer by thickening the barrier layer. This study could be an important reference for predicting how the Indian Ocean climate will respond to future changes in shortwave radiation.
2022, 41(9): 38-49.   doi: 10.1007/s13131-021-1966-0
[Abstract](322) [FullText HTML](108) [PDF 3403KB](26)
Abstract:
Time series measurements (2010–2017) from the Research Moored Array for African–Asian–Australian Monsoon Analysis and Prediction (RAMA) moorings at 15°N, 90°E and 12°N, 90°E are used to investigate the effect of the seasonal barrier layer (BL) on the mixed-layer heat budget in the Bay of Bengal (BoB). The mixed-layer temperature tendency (∂T/∂t) is primarily controlled by the net surface heat flux that remains in the mixed layer (\begin{document}${Q}^{{'}}$\end{document}) from March to October, while both \begin{document}${Q}^{{'}}$\end{document} and the vertical heat flux at the base of the mixed layer (\begin{document}${Q}_{h}$\end{document}), estimated as the residual of the mixed-layer heat budget, dominate during winter (November–February). An inverse relation is observed between the BL thickness and the mixed-layer temperature (\begin{document}$\mathrm{M}\mathrm{L}\mathrm{T}$\end{document}). Based on the estimations at the moorings, it is suggested that when the BL thickness is ≥25 m, it exerts a considerable influence on ∂T/∂t through the modulation of \begin{document}${Q}_{h}$\end{document} (warming) in the BoB. The cooling associated with \begin{document}${Q}_{h}$\end{document} is strongest when the BL thickness is ≤10 m with the \begin{document}$\mathrm{M}\mathrm{L}\mathrm{T}$\end{document} exceeding 29°C, while the contribution from \begin{document}${Q}_{h}$\end{document} remains nearly zero when the BL thickness varies between 10 m and 25 m. Temperature inversion is evident in the BoB during winter when the BL thickness remains ≥25 m with an average MLT<28.5°C. Furthermore, \begin{document}${Q}_{h}$\end{document} follows the seasonal cycle of the BL at these RAMA mooring locations, with r>0.72 at the 95% significance level.
2022, 41(9): 50-59.   doi: 10.1007/s13131-022-1989-1
[Abstract](200) [FullText HTML](65) [PDF 2660KB](17)
Abstract:
Basal melting is an important factor affecting the stability of the ice shelf. The basal channel is formed from uneven melting, which also has an important impact on the stability of the ice shelf. Therefore, it has important scientific value to study the basal channel changes. This study combined datasets of Mosaics of Antarctica, Reference Elevation Model of Antarctica (REMA) and Operation IceBridge to study the temporal and spatial changes of basal channels at the Getz Ice Shelf in Antarctica. The relationships between the cross-sectional area and width of basal channel and those of its corresponding surface depression were statistically analyzed. Then, the changes of the basal channels of Getz Ice Shelf were derived from the ICESat observations and REMA digital elevation models (DEMs). After a detailed analysis of the factors affecting the basal channel changes, we found that the basal channels of Getz Ice Shelf were mainly concentrated in the eastern of the ice shelf, and most of them belonged to the ocean-sourced basal channel. From 2009 to 2016, the total length of the basal channel has increased by approximately 60 km. Affected by the warm Circumpolar Deep Water (CDW), significant changes in the basal channel occurred in the middle reaches of the Getz Ice Shelf. The change of the basal channels at the edge of the Getz Ice Shelf is significantly weaker than that in its middle and upper reaches. Especially in 2005–2012, the eastward wind on the ocean wind field and the westward wind around the continental shelf caused the invasion and upwelling of CDW. Meanwhile, the continuous warming of deep seawater also caused the deepening of the basal channel. During from 2012 to 2020, the fluctuations of the basal channels seem to be caused by the changes in temperature of CDW.
2022, 41(9): 60-70.   doi: 10.1007/s13131-022-1997-1
[Abstract](113) [FullText HTML](29) [PDF 1139KB](10)
Abstract:
In variational methods, coupled parameter optimization (CPO) often needs a long minimization time window (MTW) to fully incorporate observational information, but the optimal MTW somehow depends on the model nonlinearity. The analytical four-dimensional ensemble-variational (A-4DEnVar) considers model nonlinearity well and avoids adjoint model. It can theoretically be applied to CPO. To verify the feasibility and the ability of the A-4DEnVar in CPO, “twin” experiments based on A-4DEnVar CPO are conducted for the first time with the comparison of four-dimensional variational (4D-Var). Two algorithms use the same background error covariance matrix and optimization algorithm to control variates. The experiments are based on a simple coupled ocean-atmosphere model, in which the atmospheric part is the highly nonlinear Lorenz-63 model, and the oceanic part is a slab ocean model. The results show that both A-4DEnVar and 4D-Var can effectively reduce the error of state variables through CPO. Besides, two methods produce almost the same results in most cases when the MTW is less than 560 time steps. The results are similar when the MTW is larger than 560 time steps and less than 880 time steps. The largest MTW of 4D-Var and A-4DEnVar are 1 200 time steps. Moreover, A-4DEnVar is not sensitive to ensemble size when the MTW is less than 720 time steps. A-4DEnVar obtains satisfactory results in the case of highly nonlinear model and long MTW, suggesting that it has the potential to be widely applied to realistic CPO.
2022, 41(9): 71-85.   doi: 10.1007/s13131-022-1999-z
[Abstract](118) [FullText HTML](33) [PDF 2080KB](9)
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The dispersion characteristics of shallow water can be described by the dispersion curves, which contain substantial ocean parameter information. A fast ocean parameter inversion method based on dispersion curves with a single hydrophone is presented in this paper. The method is achieved through Bayesian theory. Several sets of dispersion curves extracted from measured data are used as the input function. The inversion is performed by matching a replica calculated with a dispersion formula. The bottom characteristics can be described by the bottom reflection phase shift parameter P. The propagation range and the depth can be inverted quickly when the seabed parameters are represented by on parameter P. The inversion results improve the inversion efficiency of the seabed parameters. Consequently, the inversion efficiency and accuracy are improved while the number of inversion parameters is decreased and the computational speed of replica is increased. The inversion results have lower error than the reference values, and the dispersion curves calculated with inversion parameters are also in good agreement with extracted curves from measured data; thus, the effectiveness of the inversion method is demonstrated.
2022, 41(9): 86-106.   doi: 10.1007/s13131-022-1992-6
[Abstract](337) [FullText HTML](111) [PDF 9700KB](31)
Abstract:
The Dongfang1-1 gas field (DF1-1) in the Yinggehai Basin is currently the largest offshore self-developed gas field in China and is rich in oil and gas resources. The second member of the Pliocene Yinggehai Formation (YGHF) is the main gas-producing formation and is composed of various sedimentary types; however, a clear understanding of the sedimentary types and development patterns is lacking. Here, typical lithofacies, logging facies and seismic facies types and characteristics of the YGHF are identified based on high-precision 3D seismic data combined with drilling, logging, analysis and testing data. Based on 3D seismic interpretation and attribute analysis, the origin of high-amplitude reflections is clarified, and the main types and evolution characteristics of sedimentary facies are identified. Taking gas formation upper II (IIU) as an example, the plane distribution of the delta front and bottom current channel is determined; finally, a comprehensive sedimentary model of the YGHF second member is established. This second member is a shallowly buried “bright spot” gas reservoir with weak compaction. The velocity of sandstone is slightly lower than that of mudstone, and the reflection has medium amplitude when there is no gas. The velocity of sandstone decreases considerably after gas accumulation, resulting in an increase in the wave impedance difference and high-amplitude (bright spot) reflection between sandstone and mudstone; the range of high amplitudes is consistent with that of gas-bearing traps. The distribution of gas reservoirs is obviously controlled by dome-shaped diapir structural traps, and diapir faults are channels through which natural gas from underlying Miocene source rocks can enter traps. The study area is a delta front deposit developed on a shallow sea shelf. The lithologies of the reservoir are mainly composed of very fine sand and coarse silt, and a variety of sedimentary structural types reflect a shallow sea delta environment; upward thickening funnel type, strong toothed bell type and toothed funnel type logging facies are developed. In total, 4 stages of delta front sand bodies (corresponding to progradational reflection seismic facies) derived from the Red River and Blue River in Vietnam have developed in the second member of the YGHF; these sand bodies are dated to 1.5 Ma and correspond to four gas formations. During sedimentation, many bottom current channels (corresponding to channel fill seismic facies) formed, which interacted with the superposed progradational reflections. When the provenance supply was strong in the northwest, the area was dominated by a large set of delta front deposits. In the period of relative sea level rise, surface bottom currents parallel to the coastline were dominant, and undercutting erosion was obvious, forming multistage superimposed erosion troughs. Three large bottom current channels that developed in the late sedimentary period of gas formation IIU are the most typical.
2022, 41(9): 107-116.   doi: 10.1007/s13131-022-2002-8
[Abstract](123) [FullText HTML](30) [PDF 4428KB](12)
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The canyon system, including 17 small slope-confined canyons in the Shenhu area, northern South China Sea, is significantly characterized by mounded or undulating features on the canyon flanks and canyon heads. However, the mechanism underlying the formation of these features has yet to be elucidated. In previous studies, most of them were interpreted as sediment deformation on the exploration seismic profiles. In this paper, we collected high-resolution bathymetric data, chirp profiles and geotechnical test data to investigate their detailed morphology, internal structures, and origin. The bathymetric data indicated that most mounded seismic units have smooth seafloors and are separated by grooves or depressions. The distance between two adjacent mounded units is only hundreds of meters. On chirp profiles, mounded seismic units usually exhibit chaotic reflections and wavy reflections, of which the crests migrate upslope. The slope stability analysis results revealed that the critical angle of the soil layers in the study area tends to be 9°, indicating that most mounded seismic units on the canyon flanks and heads are stable at present. The terrain characteristics and seismic configurations combined with the slope stability analysis results indicated that most mounded seismic units are not sediment deformation but depositional structures or mixed systems composed of deformation and depositional structures.
2022, 41(9): 117-126.   doi: 10.1007/s13131-022-2003-7
[Abstract](86) [FullText HTML](21) [PDF 2366KB](4)
Abstract:
The stress state and rock mechanical properties govern the growth of faults and fractures, which constitute shallow hydrothermal pathways and control the distribution of seafloor massive sulfide (SMS) mounds in the seafloor hydrothermal field. The stress field has an important influence on the formation and persistence of hydrothermal pathways. Based on multibeam bathymetric data from the Trans-Atlantic Geotraverse (TAG) field, we establish two three-dimensional geological models with different scales to simulate the stress field, which investigate the characteristics of hydrothermal pathways and associated SMS mounds. The simulation results show that oblique faults and fissures form in the tensile stress zone and that mounds, including active and inactive hydrothermal mounds form in the compressive stress zone. Fault activity, which is related to the stress field, affects the opening and closing of hydrothermal channels and changes the permeability structure of subseafloor wall rock. Therefore, the stress field controls the development and persistence of shallow hydrothermal pathways. The features of shallow hydrothermal pathways in the stress field can provide geomechanical information that is useful for identifying favorable zone for SMS deposit formation.
2022, 41(9): 127-136.   doi: 10.1007/s13131-021-1972-2
[Abstract](124) [FullText HTML](37) [PDF 2282KB](23)
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Laboratory visual detection on the hydrate accumulation process provides an effective and low-cost method to uncover hydrate accumulation mechanisms in nature. However, the spatial hydrate distribution and its dynamic evolutionary behaviors are still not fully understood due to the lack of methods and experimental systems. Toward this goal, we built a two-dimensional electrical resistivity tomography (ERT) apparatus capable of measuring spatial and temporal characteristics of hydrate-bearing porous media. Beach sand (0.05–0.85 mm) was used to form artificial methane hydrate-bearing sediment. The experiments were conducted at 1°C under excess water conditions and the ERT data were acquired and analyzed. This study demonstrates the utility of the ERT method for hydrate mapping in laboratory-scale. The results indicate that the average electrical conductivity decreases nonlinearly with the formation of the hydrate. At some special time-intervals, the average conductivity fluctuates within a certain scope. The plane conductivity fields evolve heterogeneously and the local preferential hydrate-forming positions alternate throughout the experimental duration. We speculate that the combination of hydrate formation itself and salt-removal effect plays a dominant role in the spatial and temporal hydrate distribution, as well as geophysical parameters changing behaviors during hydrate accumulation.
2022, 41(9): 137-148.   doi: 10.1007/s13131-022-1996-2
[Abstract](118) [FullText HTML](34) [PDF 5858KB](11)
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Smaller mesoscale eddies (SMEs) have an important effect on the transmission of ocean temperatures, salinity, energy, and marine biochemical processes. However, traditional altimeters, the dominant sensors used to identify and track eddies, have made it challenging to observe SMEs accurately due to resolution limitations. Eddies drive local upwelling or downwelling, leaving signatures on sea surface temperatures (SSTs) and chlorophyll concentrations (Chls). SST can be observed by spaceborne infrared sensors, and Chl can be measured by ocean color remote sensing. Therefore, multisatellite observations provide an opportunity to obtain information to characterize SMEs. In this paper, an eddy detection algorithm based on SST and Chl images is proposed, which identifies eddies by characterizing the spatial and temporal distribution of SST and Chl data. The algorithm is applied to characterize and analyze SMEs in the Kuroshio Extension. Statistical results on their distribution and seasonal variability are shown, and the formation processes are preliminarily discussed. SMEs generation may be contributed by horizontal strain instability, the interaction of topographic obstacles and currents, and wind stress curl.
2022, 41(9): 149-157.   doi: 10.1007/s13131-022-1988-2
[Abstract](107) [FullText HTML](29) [PDF 15506KB](8)
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2022, 41(9): 158-168.   doi: 10.1007/s13131-022-2004-6
[Abstract](162) [FullText HTML](66) [PDF 2483KB](16)
Abstract:
This study presents an efficient Boussinesq-type wave model accelerated by a single Graphics Processing Unit (GPU). The model uses the hybrid finite volume and finite difference method to solve weakly dispersive and nonlinear Boussinesq equations in the horizontal plane, enabling the model to have the shock-capturing ability to deal with breaking waves and moving shoreline properly. The code is written in CUDA C. To achieve better performance, the model uses cyclic reduction technique to solve massive tridiagonal linear systems and overlapped tiling/shared memory to reduce global memory access and enhance data reuse. Four numerical tests are conducted to validate the GPU implementation. The performance of the GPU model is evaluated by running a series of numerical simulations on two GPU platforms with different hardware configurations. Compared with the CPU version, the maximum speedup ratios for single-precision and double-precision calculations are 55.56 and 32.57, respectively.
2022, 41(9): 169-181.   doi: 10.1007/s13131-022-1993-5
[Abstract](130) [FullText HTML](34) [PDF 7264KB](7)
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Information on the Arctic sea ice climate indicators is crucial to business strategic planning and climate monitoring. Data on the evolvement of the Arctic sea ice and decadal trends of phenology factors during melt season are necessary for climate prediction under global warming. Previous studies on Arctic sea ice phenology did not involve melt ponds that dramatically lower the ice surface albedo and tremendously affect the process of sea ice surface melt. Temporal means and trends of the Arctic sea ice phenology from 1982 to 2017 were examined based on satellite-derived sea ice concentration and albedo measurements. Moreover, the timing of ice ponding and two periods corresponding to it were newly proposed as key stages in the melt season. Therefore, four timings, i.e., date of snow and ice surface melt onset (MO), date of pond onset (PO), date of sea ice opening (DOO), and date of sea ice retreat (DOR); and three durations, i.e., melt pond formation period (MPFP, i.e., MO–PO), melt pond extension period (MPEP, i.e., PO–DOR), and seasonal loss of ice period (SLIP, i.e., DOO–DOR), were used. PO ranged from late April in the peripheral seas to late June in the central Arctic Ocean in Bootstrap results, whereas the pan-Arctic was observed nearly 4 days later in NASA Team results. Significant negative trends were presented in the MPEP in the Hudson Bay, the Baffin Bay, the Greenland Sea, the Kara and Barents seas in both results, indicating that the Arctic sea ice undergoes a quick transition from ice to open water, thereby extending the melt season year to year. The high correlation coefficient between MO and PO, MPFP illustrated that MO predominates the process of pond formation.
2022, 41(9): 182-191.   doi: 10.1007/s13131-022-1994-4
[Abstract](151) [FullText HTML](33) [PDF 793KB](7)
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In this paper, we propose a hybrid forecasting model to improve the forecasting accuracy for depth-averaged current velocities (DACVs) of underwater gliders. The hybrid model is based on a discrete wavelet transform (DWT), a deep belief network (DBN), and a least squares support vector machine (LSSVM). The original DACV series are first decomposed into several high- and one low-frequency subseries by DWT. Then, DBN is used for high-frequency component forecasting, and the LSSVM model is adopted for low-frequency subseries. The effectiveness of the proposed model is verified by two groups of DACV data from sea trials in the South China Sea. Based on four general error criteria, the forecast performance of the proposed model is demonstrated. The comparison models include some well-recognized single models and some related hybrid models. The performance of the proposed model outperformed those of the other methods indicated above.
2022, 41(9): 192-204.   doi: 10.1007/s13131-022-1987-3
[Abstract](168) [FullText HTML](28) [PDF 9663KB](12)
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Coastal wetlands are located in the ecotone of interaction between the land surface and sea, and anthropogenic activities extensively interfere with these wetlands through the reclamation of large tidal wetlands and destruction of the function of the ecosystems. In this study, we investigated the dynamic evolutionary characteristics of the Bohai Rim coastal area over the past 40 years using the Modified Normalized Difference Water Index, the fractal dimension, object-oriented classification, the land-use transfer trajectory, and regression analysis. Additionally, we quantified and monitored the evolution of reclamation and analyzed the correlation between reclamation and coastal wetlands based on 99 Landsat-2, -5, and -8 images (at 60 m and 30 m spatial resolution) over the period 1980–2019. The results are as follows. (1) The coastline of the Bohai Rim increased by 1 631.2 km from 1980 to 2019 with a zigzag variation. The artificial coastline increased by 2 946.1 km, whereas the natural coastline decreased by 90%. (2) The area of man-made wetlands increased by 3 736.9 km2, the area of construction land increased by 1 008.4 km2, and the natural wetland area decreased by 66%. The decrease of tidal flats is the main contributor to the decrease of natural wetland area (takes account for 91.1%). Coastal areas are affected by intense human disturbance, which was taken place across a large area of tidal flats and caused the landscape to fragment and be more heterogeneous. The coastal zone development activities were primarily concentrated in the southern Laizhou Bay, the Yellow River Delta, the Bohai Bay, the northern Liaodong Bay, and the Pulandian Bay. The solidified shorelines and increase in sea level have resulted in intertidal wetlands decreasing and impaired wetland ecology. (3) There is a good agreement between reclamation and the size of the coastal wetlands. Both land reclamation and the reduction in coastal wetland areas are significantly related to the population size, fishery output value, and urbanization rate. In summary, human activities, such as the construction of aquaculture ponds and salt pans, industrialization, and urbanization, are the primary forces that influence the environmental changes in the coastal region. This study is beneficial for establishing and improving the systems for the rational development and utilization of natural resources, and provides theoretical references for restoring wetland ecology and managing future reclamation activities in other coastal zone-related areas.