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Marine primary production and terrestrial input are the main sources of buried carbon in sediments of marginal seas. Only marine-source carbon buried in sediments, fixed and stored by marine ecosystems, belongs to "blue carbon" and reflects marine ecosystems' carbon sink function. The pattern of buried blue carbon in sediments, its flux, and its relationship with environmental changes remain unclear. The study aimed to investigate the composition of blue carbon in the sediments of Sanggou Bay, a special type of marginal sea. The analysis of sediment carbon sources was conducted through the C/N ratio and microscopic examination. The study also examined the long-term changes in the blue carbon burial fluxes. Results showed Blue carbon, which is sea-sourced carbon, accounted for about 23% of the total carbon content and its concentration ranged from 0.17% to 0.51%, with an average of about 0.25% ± 0.10%. The content of organic blue carbon in this sea area ranges from 0.09% to 0.26%, with an average of around 0.18% ± 0.04%. It constitutes approximately 72% of the buried blue carbon in the sediment, making it the primary component of buried blue carbon. Meanwhile, the content of inorganic blue carbon ranges from 0.01% to 0.32%. Over the past 70 years, the burial fluxes of sedimentary blue carbon, organic blue carbon and inorganic blue carbon in the Sanggou Bay are about 0.54 ± 0.22 mmol/(cm²a), 0.38 ± 0.07 mmol/(cm²a) and 0.17 ± 0.22 mmol/(cm²a), respectively; their long-term changes have been significantly affected by human aquaculture activities. Large-scale raft-rack aquaculture activities have caused a reduction in water flow velocity and an increase in the deposition of particulate organic matter, which in turn has led to the burial of organic blue carbon in the sediment. Additionally, the competition between aquaculture products and small calcareous organisms, such as mussels, foraminifera, may have inhibited the growth of small calcareous organisms. We suggest this has resulted in reduced burial fluxes of inorganic blue carbon and a decrease in its proportion among total blue carbon in the sea area. Our findings imply that aquaculture activities in Sanggou Bay had a negative impact on the burial of blue carbon in the sediments. [ABSTRACT FROM AUTHOR]

Research on the interaction between depositional evolution process and marine transgression is critical to understanding the transform mechanism of sedimentary systems and guiding hydrocarbon exploration. The early Miocene witnessed the most significant sea-level rise since the Cenomanian, which resulted in extensive marine-influenced deposits worldwide. However, the relationship between the process of depositional evolution and long-term marine transgressions (>1 Ma) remains poorly understood. The Pearl River Mouth Basin in the South China Sea offers a comprehensive deposition record of the early Miocene marine transgression. This study employs high-quality 3D seismic, well-logging, and core data to investigate the impact of the early Miocene transgression on the evolutionary dynamics of the sedimentary system. The regional sea level exhibited a prolonged rise of at least 100 m during the deposition period of the Miocene Zhujiang Formation, corresponding to the long-term marine transgressive in the South China Sea. Throughout this marine transgression, depositional systems developed in the study area include tidal flats, fan deltas, meandering river deltas, and shallow marine shelf sand bodies. The marine transgression process resulted in a significant change in depositional system types, which can be divided into seven units from Unit 1 at the bottom to Unit 7 at the top. The predominant deposition environment transitioned from tidal flats in Units 1-3 to meandering river deltas in Units 4-5, and finally to shallow marine shelf systems in Units 6-7. In the early stage (Units 1-3), the regional uplifts hindered sea level transgression and caused erosion, leading to the development of small-scale proximal fan deltas. In the middle stage (Units 4-5), these regional uplifts submerged, and meandering river deltas dominated with sediments derived from distant extrabasinal sources. During the late stage (Units 6-7), regional sea levels reached their peak, transforming the entire basin into a shallow marine shelf system. Additionally, this marine transgression significantly influenced the distribution of hydrocarbon resources. Notably, the shallow marine shelf sand bodies in Units 6-7 warrant substantial attention for future exploration. This study outlines the complicated transitional processes within depositional systems during long-term marine transgression events, holding relevance for the global evolution of marginal sea basins.

The Changjiang nutrient inputs serve as an important nutrient source for Chinese coastal waters. Its nutrient flux into the estuary has increased significantly over recent several decades, which may affect regional primary production and the sulfur cycle. Using a well-validated three-dimensional biophysical and geochemical model, we quantified the response of dimethylsulfide (DMS), a biogenic volatile sulfur that could affect the Earth's climate, to the intensified Changjiang nutrient inputs. The results showed that the enhancement in the oceanic DMS fluxes (FDMS) exceeded 30% off the coastal waters including the Zhejiang coastal area, the Changjiang estuary, east of the Changjiang estuary, and Subei Shoal given the acceleration in nutrient inputs. In addition, a phenology change in the FDMS was found in the Changjiang estuary and east of the Changjiang estuary. Furthermore, the increase in the FDMS in the Changjiang estuary and Subei Shoal was ascribed primarily to the elevated surface phytoplankton biomass, while the changes in the surface phytoplankton community contributed considerably to the changes in the FDMS in the Zhejiang coastal area and east of the Changjiang estuary. And the sensitivity experiments demonstrated that mainly the elevated Changjiang dissolved inorganic phosphorus inputs led to the increase of the DMS release off these coastal waters. The ratio between the surface concentrations of dissolved inorganic nitrogen ([DIN]) and dissolved silicate ([DSi]) might be a crucial indicator for predicating the surface DMS concentration ([DMS]) under the intensified human activities; a significant positive correlation was found between the change in the surface [DMS] and [DIN]:[DSi] ratio off the coastal area in the East China Sea. [ABSTRACT FROM AUTHOR]

The Salish Sea is a marginal inland sea of the NE Pacific (NW North America) that includes the Georgia Strait-Gulf Islands Archipelago of British Columbia, Canada and the San Juan Archipelago, Strait of Juan de Fuca, and the Lower Puget Sound of Washington State, USA. This marginal seafloor has been extensively mapped and according to criteria presented and discussed at GeoHab conferences critical marine benthic habitat types are identified. One such habitat that is the focus of this paper is the deep-water sub-tidal habitat of Pacific sand lance (PSL). The PSL (Ammodytes personatus) is a critical forage fish for a variety of mammals, birds and fish including minke whales and salmon as it preys upon zooplankton and acts as an energy transfer species from the lower to higher trophic levels. Pacific sand lance seeks refuge and overwinters in sand-wave fields consisting of dynamic bedforms. The species prefers loosely packed, well-aerated, well-sorted, medium- to coarse-grain (∼1 phi [φ], 500 µm) sand that it can burrow into easily. Such geomorphic features as active dynamic bedforms provide preferable habitats for PSL and depends on specific and unique oceanographic processes that can maintain the habitat's morphology and grain sizes. Understanding these processes is essential in forecasting alteration or destruction of such features, including changes that may be brought about by sea level rise. Using the five-person submersible Cyclops 1, we recently examined a well-studied sand-wave field in the San Juan Archipelago of Washington State, USA, which has been reported to harbor up to 12 million PSL. Observations, video recordings, and photography from this vehicle allowed us to assess modern seafloor processes of the central Salish Sea that can be used along with fish and sediment sample data to determine physical preferences this fish needs to sustain its population. Changes in the seafloor current regime, sediment source, and anthropogenic disturbances can critically alter these dynamic bedforms. This research provides insight into the structure of these bedforms, their composition, their persistence, their resilience to disturbance, and the susceptibility as an impact and becoming impacted.

Using multisource sea ice fusion data, the spatiotemporal characteristics of sea ice cover were analyzed for the marginal seas of East Asia for the period 2005–2021. The results show that there were obvious differences in the beginning and end dates of the sea ice in the different sea areas. The northern Sea of Japan had the longest ice period, and Laizhou Bay and Bohai Bay in the Bohai Sea had the shortest ice period. The time when the largest sea ice extent appeared was relatively stable and mostly concentrated in late January to mid-February. There were obvious spatial differences in the duration of the sea ice cover in the marginal seas of East Asia. The duration of the sea ice cover gradually decreased from high latitude to low latitude and from nearshore to open seas. The annual average duration of the sea ice cover was more than 100 days in most of the Sea of Japan and approximately 20 days in most of Laizhou Bay and Bohai Bay. The melting speed was significantly faster than the freezing speed in the Bohai Sea and Yellow Sea, resulting in asymmetric changes in the daily sea ice extent in the two seas. The increasing trends in the maximum sea ice extent and total sea ice extent were 0.912 × 105 km2/10 yr and 0.722 × 107 km2/10 yr, respectively, from 2005 to 2013, both of which passed the significance test at the 0.05 level. [ABSTRACT FROM AUTHOR]

The western North Pacific and its marginal seas are known for having the highest biological productivity in the world's oceans. Although vertical turbulent mixing is considered important in transporting nutrients to maintain primary production, no research into vertical turbulent nutrient flux based on microstructure measurements has been conducted in this area. Observational and numerical studies over the continental slope in the southeastern Bering Sea indicate the relevance of vertical nitrate and iron flux induced by tidal mixing for maintaining high summer primary production. This research also suggests that the abrupt topography in the path of the Kuroshio and Tsugaru Warm Current act as a hotspot for vertical turbulent nitrate transport from the lower layer. Finally, this article discusses the future direction of nutrient flux observations. [ABSTRACT FROM AUTHOR]

[Display omitted] • The semi-closed South China Sea is receiving considerable microplastics (MPs). • We reviewed MP distribution and characteristics in the South China Sea. • The magnitude of MP abundance is of up to 7 orders in seawater. • Basin-scale circulation and regional currents influence MP transport. The South China Sea is receiving a considerable plastic discharge and is a hot place for microplastics (MPs). Characterized by seasonal basin-scale circulation and strong interaction with the western Pacific, the South China Sea is an ideal area to study the transport and fate of MPs from coast to open ocean. This paper provides a comprehensive overview of the abundance and distribution of MPs in the water and sediment of the South China Sea, as well as their characters such as shape, polymer type, color, and size. Seawater MPs generally showed higher abundances in the coastal than in the basin area, while abundances in sediments showed lower variance. Basin-scale circulation and regional currents or processes, such as mesoscale eddies, and upwelling could influence MPs' horizontal and vertical transport. Future research works are required to understand the role of oceanic processes on MP distributions quantitively. [ABSTRACT FROM AUTHOR]

Marine Synechococcus , a significant contributor to primary production, shows high phylogenetic diversity. However, studies on its phylogenetic composition in the Bohai Sea, the largest continental sea in China, are lacking. We sequenced rpo C1 (encodes the RNA polymerase β' subunit protein) in samples from the Laizhou Bay (LZB) and Bohai Strait (BS) in June and November using high-throughput sequencing to reveal the phylogenetic composition of Synechococcus assemblages in the bay and strait areas of the Bohai Sea. In total, 12 lineages representing Synechococcus subclusters S5.1, S5.2, and S5.3 were identified. Spatially, clade I was obligately dominant in BS. In contrast, the Synechococcus assemblage in LZB was more diverse, with clades VI and III being highly abundant. In addition, we detected strong variation in Synechococcus structure between June and November in the Bohai Sea. Clades II, III, XX, and miyav were only detected in November. Vertically, variation in Synechococcus assemblage was not apparent among the water layers probably due to the shallow water depth with intense water mixing. Results of redundancy analysis (RDA) and random forest (RF) analysis together highlighted the key role of silicate in the Synechococcus assemblage. Our results suggested that the Bohai Sea provides various niches for different Synechococcus clades, resulting in a special phylogenetic composition of the Synechococcus assemblage, compared with that in the adjacent shelf sea and other continental seas in the world. [ABSTRACT FROM AUTHOR]

Dissolved organic nitrogen (DON) is an important component of the marine nitrogen (N) inventory and plays an essential role in N cycling in global estuaries and marginal seas. Understanding DON cycling is important but challenging. Global estuaries and marginal seas are experiencing significant anthropogenic impacts and have intensive physical/biochemical gradients. Therefore, high-quality DON concentration and N-isotope (δ15N–DON) data are very difficult to obtain. To enrich this knowledge, we take the Changjiang Estuary and the adjacent East China Sea shelf seas as a representative example and analyzed multiple isotopes and the concentrations of nitrate (NO3−), particulate nitrogen (PN), and DON. N isotopes combined with optimum multiparameter analysis proved to be very informative. This integrated analysis discriminates active DON production and consumption from a seemingly conservative distribution pattern of DON. The study area was divided into DON production zones 1 and 2 (P-zone 1 and 2) and DON consumption zones 1 and 2 (C-zone 1 and 2). For P-zone 1, the PN-originated DON elevated the δ15N–DON, while in P-zone 2, the DON excreted by phytoplankton was characterized by low δ15N and lowered δ15N–DON. DON consumption occurred in the NO3− depleted surface waters (C-zone 1) as well as the shelf middle and bottom waters (C-zone 2). This study discovers and consolidates the active and dynamical zoning of DON cycling from the estuary to the offshore marginal sea and establishes a useful means that is of valuable reference to DON cycling studies in global estuaries and marginal seas.

Marine Synechococcus, a significant contributor to primary production, shows high phylogenetic diversity. However, studies on its phylogenetic composition in the Bohai Sea, the largest continental sea in China, are lacking. We sequenced rpoC1 (encodes the RNA polymerase β’ subunit protein) in samples from the Laizhou Bay (LZB) and Bohai Strait (BS) in June and November using high-throughput sequencing to reveal the phylogenetic composition of Synechococcus assemblages in the bay and strait areas of the Bohai Sea. In total, 12 lineages representing Synechococcus subclusters S5.1, S5.2, and S5.3 were identified. Spatially, clade I was obligately dominant in BS. In contrast, the Synechococcus assemblage in LZB was more diverse, with clades VI and III being highly abundant. In addition, we detected strong variation in Synechococcus structure between June and November in the Bohai Sea. Clades II, III, XX, and miyav were only detected in November. Vertically, variation in Synechococcus assemblage was not apparent among the water layers probably due to the shallow water depth with intense water mixing. Results of redundancy analysis (RDA) and random forest (RF) analysis together highlighted the key role of silicate in the Synechococcus assemblage. Our results suggested that the Bohai Sea provides various niches for different Synechococcus clades, resulting in a special phylogenetic composition of the Synechococcus assemblage, compared with that in the adjacent shelf sea and other continental seas in the world.

The influence of the exceptionally strong typhoon Mangkhut on the availability of nutrients and changes in primary production were studied in the northern South China Sea in September 2018. A tight station grid was sampled to analyze major nutrients, chlorophyll_a, particulate and dissolved organic carbon and nitrogen. Based on interpolated profiles, nutrients and organic matter budgets were determined for the upper 100 m of the water column prior to and after Mangkhut's passage. An upper layer of 100 m was found to reflect the important changes by the typhoon. Considerable differences between the on‐shelf, shelf edge and the deep‐sea stations were determined. Nitrate and phosphate increased by about 80% and 36% on the shelf, respectively, and both by almost 40% at the shelf edge. The open deep‐sea part of the study area reflects some deviating results that may be caused by just displacement of water or by mixing water of different origin. However, right on Mangkhut's track on the shelf even contact between surface waters and bottom waters was enabled, increasing phosphate and silicate, but declining nitrate. The inventory of organic carbon of the upper 100 m of the study area (138,000 km2) of 92 Gmol had increased within a few days after the typhoon's passage by 5 Gmol on the shelf and about 2 Gmol in the shelf edge area. Chlorophyll_a doubled during our stay and might have reached a factor of 3 increase in the subsequent time by nitrate supply and excess phosphate. Plain Language Summary: The influence of the super typhoon Mangkhut on the waters of the northern South China Sea was studied in September 2018. Nutrients and organic material were measured on 63 stations from the Chinese research vessel HAI YANG DI ZHI SHI HAO. Amounts of nutrients and biogenic matter were calculated for the on‐shelf, shelf edge and deep‐sea stations for the pre‐ and post‐Mangkhut period. An important finding was that the stations of the different areas, on‐shelf, shelf edge and the deep‐sea appeared to be differently impacted by Mangkhut. Even differences between the stations right on its track and in the other parts of the study area were found. In general, nutrients were supplied in enormous amounts and caused immediate algae growth. Moreover, enough nutrients were supplied to support algae growth for a couple of weeks. In summary, it was found that Manghut's upper water column mixing and shifting caused an almost tripling of primary production compared to the normal situation. Key Points: The typhoon Mangkhut clearly impacted the water column differently on the continental shelf, at the shelf edge and in the deep seaOn Mangkhut's track a maximum nitrate supply of 162 mmol m−2 was caused by induced upwelling at the shelf edgeThe chlorophyll inventory of 2.8 Gg was almost tripled by contributing 4.7 Gg estimated from an additional nutrient supply [ABSTRACT FROM AUTHOR]

Branched glycerol dialkyl glycerol tetraethers (brGDGTs) are components of bacterial membranes in terrestrial soils, which are widely used in paleoenvironmental reconstruction in global terrestrial soils and marine sediments. In marine sediments, the mixed sources of brGDGTs complicate the applications of brGDGT-related indicators in reconstructing terrestrial environments. In this study, we reported the spatial distribution of brGDGT-related indicators (MBTʹ 5ME, CBTʹ 5ME, #Ringstetra, and IIIa/IIa) in surface sediments from the East China Sea (ECS). MBTʹ 5ME and CBTʹ 5ME showed a stepped trend from the inner shelf to the outer shelf, and #Ringstetra and ∑IIIa/∑IIa values in sediments of the ECS are distinct compared with those in the catchment soils, suggesting marine in situ production of brGDGTs. We also examined the existence of marine in situ brGDGTs and quantitatively determined the contributions of terrestrial and in situ production of brGDGTs. This study reported mixed sources of soil-derived brGDGTs were dominant, and marine in situ brGDGTs were overprinted. Our results indicate that there were predominantly marine in situ brGDGTs (avg. 60.5 ± 5.5%) in the outer shelf due to the weak riverine transportation and were characterized by high #Ringstetra and IIIa/IIa.

Using multisource sea ice fusion data, the spatiotemporal characteristics of sea ice cover were analyzed for the marginal seas of East Asia for the period 2005–2021. The results show that there were obvious differences in the beginning and end dates of the sea ice in the different sea areas. The northern Sea of Japan had the longest ice period, and Laizhou Bay and Bohai Bay in the Bohai Sea had the shortest ice period. The time when the largest sea ice extent appeared was relatively stable and mostly concentrated in late January to mid-February. There were obvious spatial differences in the duration of the sea ice cover in the marginal seas of East Asia. The duration of the sea ice cover gradually decreased from high latitude to low latitude and from nearshore to open seas. The annual average duration of the sea ice cover was more than 100 days in most of the Sea of Japan and approximately 20 days in most of Laizhou Bay and Bohai Bay. The melting speed was significantly faster than the freezing speed in the Bohai Sea and Yellow Sea, resulting in asymmetric changes in the daily sea ice extent in the two seas. The increasing trends in the maximum sea ice extent and total sea ice extent were 0.912 × 105 km2/10 yr and 0.722 × 107 km2/10 yr, respectively, from 2005 to 2013, both of which passed the significance test at the 0.05 level.

Through photosynthesis, phytoplankton initiate material cycling and the flow of energy through marine ecosystems. The structure of marine ecosystems is sensitive to the size of primary producers, and size-specific photosynthesis-irradiance (P-I) parameters are required for modeling the size-specific primary production. We defined a phytoplankton type to be a group of phytoplankton communities with similar compositions and hypothesized that a function of phytoplankton types might be used to quantify systematic differences of P-I parameters between size classes (structural effects) and variations of the magnitudes of those parameters if the overlap between habitats was small (environmental effects). To test this hypothesis, we conducted a study to measure the size-specific P-I parameters of two size classes (2 μm) and pigment-based phytoplankton community structure in a marginal sea, the Taiwan Strait. Three phytoplankton types were classified, and type-based and size-specific P-I parameters were derived. The results demonstrated the potential of a type-based model to estimate P-I parameters for two phytoplankton size classes as well as different habitats.

The repeated transgression and regression of coastlines mediated by the late Quaternary glacial–interglacial cycles make the northwest Pacific a hot spot to study marine speciation and population diversity. The red alga Agarophyton vermiculophyllum is an ecologically important species native to the northwest Pacific, capturing considerable research interest due to its wide-range invasiveness in Europe and North America. However, the knowledge of phylogeographic structure and intraspecific genetic diversity across the entire native range was still scarce. Here, we used 1,214-bp of mitochondrial cytochrome c oxidase subunit 1 (cox1) to explore phylogeographic patterns, lineage structure, and population genetic differentiation of 48 A. vermiculophyllum populations in the northwest Pacific. Our DNA data revealed overall high haplotype diversity and low nucleotide diversity and five phylogeographically structured genetic lineages that diverged significantly from each other. S-DIVA analysis showed the ancestors of A. vermiculophyllum originating from multiple areas encompassing the Japan–Pacific coast, East and South China Seas. This combined evidence indicates that A. vermiculophyllum might have survived in multiple scattered glacial refugia during the late Quaternary climate oscillations in the northwest Pacific. Such knowledge may help to better understand how palaeoclimate interacted with contemporary environments to contribute to intraspecific genetic variation and provide a new perspective for conserving natural resource of A. vermiculophyllum in the northwest Pacific.

This study investigates the impacts of marginal sea surface temperature (SST) on temperature variations over the Korean Peninsula in winter via observation data analysis and numerical model simulation. The marginal SST variability is represented using ocean temperature variations at the Ieodo Ocean Research Station (IORS), wherein the oceanic and atmospheric variables are observed in real-time. The wind efficiency is defined as the Korean temperature response to given winds related to variability of Korean temperature. Based on the strong correlation between SST and land temperature, the wind efficiency is determined to estimate the effect of ocean temperature variation on the land temperature. Results confirmed that the wind efficiency is closely related to the marginal SST by modulating latent and sensible heat flux, which considerably affects the climate variation over the Korean Peninsula. A significant lagged relation between the wind efficiency and marginal SST further supports this finding. The numerical experiment using the weather research and forecasting model (WRF) has strong agreement with the observational analysis. Thus, real-time ocean observational data at IORS can be used as an indicator of climate prediction over the Korean Peninsula. [ABSTRACT FROM AUTHOR]

Rapid developments of deep-sea researches in China over the past 20 years have promoted the South China Sea (SCS) into the international deep-sea frontiers. The "three deep technologies", namely scientific drilling, long-term seafloor observation and deep submersible vehicles implemented successively in SCS studies helped to achieve a number of scientific breakthroughs. Over the 20 years, five international ocean drilling expeditions to the SCS recovered nearly 10 km of sediment cores from sites at 3–4 km water depths, and drilling into the magmatic basement at 6 sites shed light on the genesis of the SCS basin. Coupled with other deep-sea short core sediments from the SCS, these records demonstrate evidence that water and carbon cycling in the low latitude regions can directly respond to the orbital forcing, and subsequently nurture a new concept of low-latitude forcing of climate changes, which challenges the classical wisdom of the overwhelming role played by the Arctic ice-sheet in climate changes. The exploration in the continent-ocean transition zone also reveals a number of specific features that characterize the SCS as a marginal basin formed at the subduction zone in the Western Pacific. The features include active magmatism and rapid rupture of lithosphere through the basin formation process, and imply that "the SCS is not a mini-Atlantic" as they can be distinguished as "plate-edge rifting" and "inner-plate rifting" respectively, thus challenging the universality of the Atlantic model for passive margins. Many more discoveries can be assembled from long-term mooring observations and deep diving cruises in the deep SCS, such as the cyclonic nature of the deep-water circulation, deep-water sediment transport by contour currents and turbidites, manganese nodules, extinct hydrothermal vents, and cold-water coral forests. In addition, prominent progress achieved in microbiology and biogeochemistry includes the microbial carbon pump and the coupling of carbon and nitrogen cycles. Clearly, most achievements of the deep-sea explorations in the SCS over the last 20 years have always been of international scale and impact. However, the contributions from Chinese scientists are most prominent, particularly with the research activities undertaken from the major program "Deep Sea Processes and Evolution of the South China Sea (2011–2018)" supported by the National Natural Science Foundation of China. [ABSTRACT FROM AUTHOR]

East Asia and South America have both experienced long-term subduction since at least the Jurassic, but they have had contrasting tectonic evolutions since the Late Cretaceous. East Asia was dominated by extensional tectonics with many marginal sea basins forming during the Cenozoic while South America was dominated by compressional tectonics building the Andean mountains. The mechanism controlling this contrast in tectonic style on opposite sides of the Pacific has been unclear. We suggest that the deep mantle flow revealed by seismic tomography, plate reconstructions, and geodynamic models contributed to the pan-Pacific tectonic disparity. Our geodynamic models suggest that the Atlantic Ocean opening plays an important role in promoting compression-dominated tectonics and Andean building along the South American margin by allowing fast trench-ward motion of South America. On the other hand, the long-standing downwelling flow beneath the interior of Asia since Asian assembly in the Paleozoic and the early Mesozoic helps to inhibit Atlantic-type ocean opening in Asia and restrain trench-ward motion of East Asia, promoting extension-dominated tectonics along the Asian margin. The restrained trench-ward motion suggests a low probability of flat-slab subduction occurrence in East Asia during the late Mesozoic. • South Atlantic Ocean opening allows fast trench-ward motion of South America. • Atlantic Ocean opening promotes compression-dominated South America tectonics. • Slow trench-ward continental motion promotes extension-dominated East Asia tectonics. • Long-standing downwelling flow beneath Asia inhibits Atlantic-type ocean formation. • Low possibility of flat-slab subduction beneath East Asia during the late Mesozoic. [ABSTRACT FROM AUTHOR]

Abstract We evaluated the factors that control the variability in dissolved cadmium (Cd d), phosphate (PO 4 3−) and the Cd d /PO 4 3− ratio in the upper 1000 m of the deep region of the Gulf of Mexico (GoM), a marginal sea where trace element data are limited. These variables were compared to data from studies of adjacent areas (in the Western Central Atlantic), related to physical processes (mesoscale structures and upwelling events) occurring inside the GoM, and to dinoflagellate and diatom abundances in surface waters of this region. Vertical distributions of Cd d concentrations and the Cd d /PO 4 3− ratio displayed the typical nutrient profile that has been extensively reported for different oceans. Cd d and PO 4 3− concentrations in the GoM were higher than those in the Western Central Atlantic. The slope of the Cd d vs. PO 4 3− relationship for samples within the Loop Current (LC) in the GoM was similar (242 pmol μmol−1, R 2 = 0.96) to that calculated for the Western Central Atlantic waters (same depth range) that reach the GoM through the LC (235 pmol μmol−1, R 2 = 0.98). The linear regression for all the GoM samples, though having a similar slope (249 pmol μmol−1), presented a larger deviation (R 2 = 0.91). We propose that this deviation is due to spatial inhomogeneity that can be explained by 1) preferential remineralization of PO 4 3− vs. Cd d at subsurface waters in some regions, 2) Cd d inputs from the north, transported by mesoscale processes, and 3) interactions with the continental slope at the minimum O 2 layer. Local changes in the relationship between Cd d and PO 4 3− were traced with Cd*, which represents the deviation of measured Cd to that expected by the deep-water Cd d vs. PO 4 3− relationship. Cd* presented mainly negative values at surface and subsurface waters (~150 m) indicating preferential uptake of Cd d vs. PO 4 3− by the phytoplankton at the surface and preferential remineralization of PO 4 3− vs. Cd d from the organic matter at the subsurface waters. At deeper waters (~400–1000 m) Cd d was preferentially remineralized. In order to understand the inhomogeneity of the horizontal distribution of Cd d , PO 4 3− and the Cd d /PO 4 3− ratio in surface waters, three regions were defined considering their biological and physical characteristics. These were: I) the Oligotrophic region (in the northwest GoM) where the variability in the Cd d /PO 4 3− ratio was largely explained by salinity, II) the Upwelling region (off the coast of the Yucatan Peninsula) where the variability in the Cd d /PO 4 3− ratio was principally due to the diatom abundance and, III) Semi-permanent Cyclonic Gyre region (Bay of Campeche) where the variability in Cd d and the Cd d /PO 4 3− ratio were primarily influenced by the upwelling generated by the cyclonic gyre, and the variability in PO 4 3− was likely due to the consumption of this nutrient by phytoplankton. In summary, physical processes, river inputs, and phytoplankton abundance appear to play an important role in explaining the spatial variation in the Cd d /PO 4 3− ratio. Highlights • Dissolved Cd (Cd d) and PO 4 3− are enriched in the Gulf of Mexico (GoM). • Cd d and PO 4 3− concentration distributions showed high spatial variation in the GoM. • The GoM and Western Central Atlantic waters exhibit similar Cd d vs. PO 4 3− slopes. • Biological and mesoscale processes control the Cd d /PO 4 3− ratio in the GoM. [ABSTRACT FROM AUTHOR]

Abstract Iodirne-129 is useful for tracking water mass movement in the ocean. In this study, the concentration of iodine isotopes in seawater of the East China Sea (ECS) in October 2013 were analyzed to investigate the spatial and vertical distribution of 129I and 127I to understand water mass exchange. Results showed that the 129I/127I atomic ratios varied with the water mass, with higher values of (10–20) × 10−11 in the coastal regions and lower values of <8 × 10−11 offshore. Inventories of 129I were estimated to be (0.23–1.7) × 1012 atoms m−2 (n = 18) in upper 100 m waters, which is comparable to those of other regions without being contaminated by the nuclear accidents or nuclear reprocessing facilities. The total amount of 129I in the ECS water column was estimated to be 88 g in which over 90% is attributed to the oceanic input (e.g., West Pacific) via the Kuroshio Current (KC). The contributions of 129I from Changjiang (Yangtze River) terrestrial watershed (<7.5%) and atmospheric fallout (<2.7%) were small. Those from the Fukushima accident were negligible during this investigation. The 129I/127I ratios versus salinity distribution showed the range and stratification of the Changjiang, Yellow Sea, and KC waters in the ECS. Our study shows that the Changjiang fresh water could be transported to the North Jiangsu coast in October; the Taiwan Warm Current water could intrude to Northern part of the Changjiang Estuary (32°N). Besides, our results suggest that the 129I/127I profile is useful to indicate the seawater mixing process in ocean marginal systems. Graphical abstract Unlabelled Image Highlights • Iodine-129 is useful for understanding water mass movement in the ocean. • 129I/127I atomic ratios varied with the water mass in the East China Sea. • Oceanic input dominates the 129I inventory. • Vertical profiles of 129I provide information for studying mixing processes. • 129I/127I is useful for tracing the water mass exchange and land-sea interaction. [ABSTRACT FROM AUTHOR]

Provenance analyses on sediments from depositional sinks have provided valuable information about the birth of the Pearl River, a key event in the landscape history of South China. However, uncertainty remains due to the difficulty in clearly identifying the source regions by geochemical or geochronological approaches, giving rise to disputes on the driving mechanisms underlying river network evolution. Here we combined pollen and grain-size analyses of terrigenous sediments from International Ocean Discovery Program site U1501 to further constrain the timing and pattern of the Pearl River network evolution during the late Eocene and Oligocene. The results reveal a sharp, synchronous transition at ∼32 Ma in both proxies. The sudden occurrence of the rainforest coniferous pollen Dacrydium and increased abundances of the alpine coniferous pollen Abies / Picea indicate a new mountainous source region stretching across the tropical-subtropical ecotone after 31.5 Ma. The simultaneous input of a distinct coarse fraction of siliciclastic components implied that the terrigenous sediments were transported by a large, regional-scale river, in addition to the preceding small rivers draining local uplifts proximal to the site. The formation of a proto-Pearl River originating from the Cathaysian mountains and flowing through the rift basins of the continental margin is thus proposed. Moreover, when integrated with co-located calcareous nannofossil records indicative of a synchronous deepening process of the sea basin, our results link this early river network reorganization event to the spreading of the South China Sea rather than to the uplift of the Tibetan Plateau. • Eocene to Oligocene pollen and grain-size records of IODP site U1501. • Rapid provenance changes in the South China Sea at ∼32 Ma. • Formation of the proto-Pearl River across the rifted continental margin at ∼32 Ma. • A clear link between the river network evolution and sea-floor spreading. [ABSTRACT FROM AUTHOR]

Amidst the continued northward migration of tropical cyclones in the context of global warming, mid and high latitudes marginal seas, like the East China Seas in the northwest Pacific Ocean, are increasingly attacked by tropical cyclones. As such, it is crucial to pay more attention to the impact of tropical cyclones on these marginal seas. To address this issue, we utilized a well-calibrated FVCOM model to study the effects of Typhoon Lekima (2019) on sediment transport between the Bohai Sea and the Yellow Sea. The results showed that during Typhoon Lekima's passage, sediment dynamics in the Bohai and Yellow seas were significantly altered. During the first two days of Typhoon Lekima's arrival, the water and sediment transport pattern rapidly changed from normal summer conditions to a strong inflow into the Bohai Sea, which increased water levels in the southwest Bohai Sea. As Typhoon Lekima weakened, the barotropic effect drove the water outflow from the Bohai Sea to the Yellow Sea. Strong bottom shear stress induced by the high-energy waves introduced strong sediment resuspension, which led to massive sediment escaping out of the Bohai Sea via the outflow during the weakening period of Typhoon Lekima. After two days following Typhoon Lekima's passage, the transport pattern gradually returned to normal summer conditions. The study revealed that the net sediment load from the Bohai Sea to the Yellow Sea during Typhoon Lekima was approximately 0.84 Mt., which is equivalent to 5–33% of the annual flux. The study highlights the critical role of extreme weather events in sediment dynamics and provides important insights into the impacts of typhoon on source-to-sink process in mid and high latitude marginal seas. • Typhoon induced rapid oscillation of sediment transport in Bohai and Yellow seas. • During Lekima's 6-day passage, 0.84 Mt. of sediment escaped out of the Bohai Sea. • Sediment flux during typhoon exceeded that during entire summer without typhoon. [ABSTRACT FROM AUTHOR]

Understanding bathymetric patterns of deep-sea meiofauna is important for elucidating the influence of environmental variables on the characteristics of meiofaunal community structures. Depth-dependent meiobenthic community structures were investigated on the continental shelf, slope and deep basin of the Ulleung Basin in the southeastern East Sea. Meiobenthic samples were collected at 29 stations (water depth: 74–2155 m) from the continental shelf near the Korea Strait to the southern slope and basin areas of the Ulleung Basin during the summer cruise of R/V Eardo (June 2006). In total, 15 meiobenthic taxa (between two and nine taxa at each station) were identified. Nematodes formed the most abundant taxon (53–80%), followed by benthic foraminifera (7–39%). Meiobenthic abundance varied from 295 to 3697 ind. 10 cm−2 (nematodes, 106–3319 ind. 10 cm−2) at each station. The distribution of meiobenthic animals in the Ulleung Basin showed considerable spatial trends, with higher densities on the southern slope (1083 ± 249 ind. 10 cm−2) of the Ulleung Basin than the shelf (650 ± 220 ind. 10 cm−2) or deep basin (459 ± 214 ind. 10 cm−2) regions. Among the environmental parameters, TOC (total organic carbon) concentration was significantly correlated with meiobenthic abundance (r 2=0.297), indicating that high food supply promotes meiobenthic abundance. Meiobenthic community structures showed depth-related trends from the continental shelf to the deep basin, with several meiobenthic taxa (e.g., amphipods, bivalves, harpacticoids, kinorhynchs, nauplius, nematodes, ostracods and polychaetes) contributing to these variations in the meiofauna. • Depth-dependent meiobenthic community structures were investigated. • Meiobenthic samples were collected from 29 stations of the Ulleung Basin. • Fifteen meiobenthic taxa were identified; nematodes were the most abundant taxon. • TOC concentration was significantly correlated with meiobenthic abundance. • Meiobenthic community structures showed depth-related trends. [ABSTRACT FROM AUTHOR]

Spatial variability of ammonium concentrations along repeat transects were examined on the Chukchi shelf during 2012–2018. Two distinct near-bottom high ammonium pools (>1 μmol/kg) near 67.5°N and 72.5°N of the transects were identified in all years. The accumulation of ammonium in the regions is driven primarily by a combination of biogeochemical processes (e.g., dynamic bacterial remineralization of organic matter) and physical controls (e.g., strong density-contrast barrier limits upward mixing of ammonium). The ammonium pool on the shelf may became larger in the expectation of the stronger bacterial remineralization following elevate primary production, and may have potential impact on the structure and productivity of ecosystem on the Chukchi shelf. • High ammonium concentrations were measured in near-bottom water of the Chukchi shelf during summer of 2012–2018. • The accumulation of ammonium may be caused by a combination of intense remineralization and inhibited vertical diffusion. • The ammonium pool on the shelf may became larger with elevated primary production and enhanced bacterial remineralization. [ABSTRACT FROM AUTHOR]

Abstract Extreme hydrologic events such as floods have caused catastrophic losses to modern human society, especially in highly developed coastal areas. However, high-resolution reconstructions of extreme flood events are scarce due to a paucity of suitable proxies in marginal seas. Here we present a high-resolution record of extreme flood events in the Changjiang River catchment during the last 110 years using samples from the subaqueous delta of Changjiang River estuary. We used a multi-proxy approach including Sr-Nd isotopes, Zr/Rb ratio and biomarkers (branched GDGTs, i.e. brGDGTs, and crenarchaeol, and the ratio of the two as calculated by the BIT index) as proxies for the evolution of extreme floods in the Changjiang River catchment. Rapid shifts in these proxies agreed with the timing of floods on the Changjiang River. We also tested the reliability of biomarker indices to reconstruct paleoflood events in this area. The results indicated that the abundances of GDGTs fluctuated in concert with historical floods. Cross-spectral analyses revealed that historical floods in the Changjiang River catchment were consistent with ENSO variance. Highlights • Sr-Nd isotopes and BIT were applied as Paleoflood multiproxy indices. • Zr/Rb ratio records of historical floods in core sediments had been compiled. • BIT and brGDGTs distributions co-varied with palaeoflood record in subaqueous delta. • Profiles of Sr-Nd isotopes responded to climate change coherently. [ABSTRACT FROM AUTHOR]

Abstract Based on a survey conducted from June to July 2013, aragonite saturation state variation and control in the river-dominated marginal BoHai and Yellow seas were investigated. Surface water Ω arag ranged from 2.0–3.8, whereas subsurface water Ω arag was generally lower than 2.0. Temperature changes had a strong influence on Ω arag through induced CO 2 solubility changes in seawater. Riverine freshwater input decreased Ω arag in the Changjiang and Yalu river estuaries, but induced higher Ω arag in the Yellow River estuary. Biological processes had opposite effects on Ω arag , whereby elevated biological production led to the highest Ω arag in the South Yellow Sea surface water, whereas net community respiration/remineralization induced low Ω arag in subsurface water. Stratification affected the level and scale of low Ω arag in subsurface water. By the year 2100, surface water with Ω arag > 2.0 will disappear except for the Yellow River estuary, and most of the subsurface water will develop substantial aragonite undersaturation. Highlights • Dynamics of seawater Ω arag were investigated in the BoHai and Yellow seas. • Riverine freshwater input decreased Ω arag in the Changjiang and Yalu river estuaries. • Freshwater input from the Yellow River induced high Ω arag in the estuary. • Seawater with Ω arag above 2.0 will likely disappear by the year 2100. [ABSTRACT FROM AUTHOR]

Research and protection of biodiversity is generally started with species recognizing guided by achievement of cataloguing and illustration obtained through in situ investigation data accumulation and literature learning. Facing the shortage of taxonomist, it is getting harder to maintain important specimen collections and handle loans. The West Pacific Ocean has been operating as a center of the origin of global marine biodiversity result of the richest species diversity of marine taxa found in these waters. The present work is a compilation and summary of systematics, species diversity and new taxa of mesozooplankton major group known in West Pacific Ocean and its marginal seas (0°-45°N, 105°-152°E) according to 6 203 mesozooplankton samples acquired from 701 stations during 1965 and 2008. A total of 2 657 species belonging to 686 genera and 206 families of 10 mesozooplankton groups have been found through taxonomic identification and document consulting. In details, 697 species from 251 genera of 99 families belong to the Medusozoa, 59 species from 22 genera of 12 families to the Ctenophora, 85 species from 36 genera of 14 families to the pelagic Mollusca (Pteropoda and Heteropoda), 416 species from 91 genera of 8 families to the Ostracoda, 908 species from 156 genera of 51 families to the Copepoda, 202 species from 60 genera of 4 families to the Mysidacea, 56 species from 8 genera of 2 families to the Euphausiacea, 105 species from 23 genera of 8 families to the Decapoda, 48 species from 13 genera of 5 families to the Chaetognatha and 81 species from 26 genera of 5 families to the Tunicata. The dominant species of each group are enumerated. Moreover, 2 new species of Medusozoa, Tubulariidae, Ectopleura, 1 new species of Medusozoa, Protiaridae, Halitiarella, 1 new genus and 1 new species of Medusozoa, Corymorphidae are established. An amount of 806 species are expanded with an increase of 43.5% on the basis of 1 852 species recorded before 2008, including 1.4% increase from tropical sea around equator, 4.0% from the frigid water in high latitude region, and 3.0% of bathypelagic-associated waters. The authors also summarized future prospects into five major areas in marine mesozooplankton research in China. Such information of qualitative phyletic classification could be of high relevance to studies on biodiversity and biogeography of marine mesozooplankton, especially for monographs contributed to make an overall and systematic conclusion on the species of marine life in China after 2008. [ABSTRACT FROM AUTHOR]

Marginal sea sediments receive organic substrates of different origins, but whether and to what extent sediment microbial communities are reflective of the different sources of organic substrates remain unclear. To address these questions, sediment samples were collected in two connected China marginal seas, i.e., Bohai Sea and Yellow Sea, and their two major tributaries (Yellow River and Liao River). Sediment bacterial community composition (BCC) was examined using 16S rRNA gene pyrosequencing. In addition, physicochemical variables that describe environmental conditions and sediment features were measured. Our results revealed that BCCs changed with salinity and organic carbon (OC) content. Members of Gaiellaceae and Comamonadaceae showed a rapid decrease as salinity and phytoplankton-derived OC increased, while Piscirickettsiaceae and Desulfobulbaceae exhibited an opposite distribution pattern. Differences of riverine vs. marginal sea sediment BCCs could be mostly explained by salinity. However, within the marginal seas, sediment BCC variations were mainly explained by OC-related variables, including terrestrial-derived fatty acids (Terr_FA), phytoplankton-derived polyunsaturated fatty acids (Phyto_PUFA), stable carbon isotopes (δ 13 C), and carbon to nitrogen ratio (C/N). In addition to environmental variables, network analysis suggested that interactions among individual bacterial taxa might be important in shaping sediment BCCs in the studied areas. [ABSTRACT FROM AUTHOR]

Large quantities of microplastics with small particle sizes were found in the South China Sea (SCS). The abundances of microplastics in seawater were 0.045 ± 0.093and 2569 ± 1770 particles/m 3 according to the bongo net and pumping sampling methods, respectively. Smaller-size fractions (size < 0.3 mm) contributed 92% of the number of microplastics to the total load. Continental slope is the largest reservoir of microplastics with an inventory of 295 tons. 21 polymer types were found in the samples using the micro Fourier Transform Infrared Spectroscopy (FTIR), among which alkyds (22.5%) and polycaprolactone (PCL) (20.9%) accounted for almost half of the total polymer content. Lighter plastics would not only concentrate upon the coastal area, being more likely to drift further into open seas with ocean currents. The distribution characteristics showed that it was mainly controlled by terrestrial input of the Pearl River. This study, as the first report from SCS on microplastics in water for its distribution and influence factors, provided impetus for further research on the transportation fate and the behavior of this emerging pollutant from coastal zone to the open oceans. [ABSTRACT FROM AUTHOR]

Abstract: Due to high temporal and spatial dynamics and complex biological processes, it is difficult to estimate lateral transportations of the dissolved organic carbon (DOC) in marginal seas by conventional field observations and model simulations. Taking the East China Sea (ECS), for example, this study proposed a novel model for estimating the lateral DOC flux in marginal sea. Three‐dimensional distributions of DOC concentrations were retrieved by satellite remote sensing. Furthermore, three‐dimensional currents were simulated using the numerical model. Finally, the lateral DOC flux in the whole ECS was estimated based on the satellite‐derived DOC concentrations and the simulated currents. The results showed that despite seasonal variations, the unit area lateral DOC flux remained high throughout the year in the Changjiang River estuary, Zhejiang‐Fujian Coast, Taiwan Strait, and Kuroshio regions. There were three eastward transportation channels which were strong in summer half year and weak in winter half year. Moreover, a northward transport zone extending from north of Taiwan to the south of the Changjiang River estuary was detected. In terms of annually net flux, highest net DOC import (30.65 TgC yr−1) was from the Taiwan Strait, mainly through the eastern side of the strait. The second highest net DOC import (18.75 TgC yr−1) was from the shelf slope (200 m isobath), mainly through the south part of the slope between 26°N and 26.5°N. Most of the net DOC export (−52.75 TgC yr−1) from the ECS was observed through the northern boundary (32°N), particularly in the outer shelf with water depth of 100–200 m. [ABSTRACT FROM AUTHOR]

Large parts of the Mediterranean were formed during the Mesotethys Ocean opening and subsequently became land-locked in the midst of the Africa-Eurasia plate convergence. Since the Neogene, this convergence has concealed key sections of the original basins. Previous studies widely agree that the easternmost part of the Mediterranean, the Levant Basin, opened during the Permian to Early Jurassic (PJ) and accordingly explain the architecture of the basin and its margins. However, since the PJ model was suggested in the late 1990’s a flood of new evidence has arrived since the hydrocarbon exploration, some of which do not fit in with the PJ model, and some remain unexplained. The current research re-examines the old and new evidence from the Levant basin, its margins, the surrounding landmass, the adjacent Eratosthenes Seamount and the eastern part of the Herodotus Basin. The integration of geological and geophysical data suggests that the Levant Basin formed ~100 Myr later than previously thought, i.e., during the Cretaceous. Its opening was triggered by the ‘Levant-Nubia' mantle plume that induced a sequence of wide-spread Ocean Island Basalt volcanism. The resulting crustal updoming and stretching led to the breakup of the Levant landmass since ~141 Ma, and drifting of the Eratosthenes Seamount since ~125 Ma. Back-arc extension shaped the Levant Basin as a hybrid crust comprising continental slivers intervened by oceanic patches. The basin opened during the Long Normal Cretaceous Polarity Chrons between ~122 and ~84 Ma, and therefore it does not show any magnetic lineation. The opening of the Levant basin occurred while the Herodotus basin floor subducted eastward under the Eratosthenes Seamount. The subduction hinge did a roll-back and facilitated the Seamount drifting. The Seamount absorbed intensive volcanism while chasing the subduction roll-back and sliding between two Subduction-Transform Edge Propagator (STEP) faults that bounded the stretching Levant back-arc basin. The Turonian-Maastrichtian compression stress regime, or inversion, halted the extension of the Levant Basin, stagnated its hybrid fabric, and prevented the development of a spreading center. The evolutionary scenario suggested here is a game changer for future exploration in the Levant and may serve as a global analog for the formation of marginal seas. [ABSTRACT FROM AUTHOR]

Long‐term near‐surface observations from five coastal stations, high‐resolution model data from Modern Era Retrospective‐Analysis for Research and Applications (MERRA) and high‐resolution daily sea surface temperature (SST) from National Ocean and Atmospheric Administration (NOAA) are used to investigate the climatology of sea breezes over the eastern side of the Red Sea region. Results show existence of separate sea breeze systems along different segments of the Red Sea coastline. Based on the physical character and synoptic influences, sea breezes in the Red Sea are broadly divided into three regions: the north and the middle Red Sea (NMRS), the Red Sea convergence zone (RSCZ) and the southern Red Sea (SRS) regions. On average, sea breezes developed on 67% of days of the 10‐year study period. Although sea breezes occur almost all year, this mesoscale phenomenon is most frequent from May to October (78% of the total sea breeze days). The sea breeze frequency increases from north to south (equatorwards), and sea breeze characteristics appear to vary both temporally and spatially. In addition to land–sea thermal differential, coastline shape, latitude and topography, the prevailing northwesterly at NMRS region, the convergence of northwesterly and southeasterly wind system at RSCZ region and the northeast and southwest monsoon at SRS region play an important role in defining the sea breeze characteristics over the Red Sea. [ABSTRACT FROM AUTHOR]

The absorption properties of chromophoric dissolved organic matter (CDOM) in the East China Sea (ECS) and the waters off eastern Taiwan (WET) were studied during May 2014. CDOM absorption coefficient ( a 280 ) and spectral slope ( S 275–295 ) revealed considerable spatial variations. In the ECS, the values of a 280 and S 275–295 presented a reverse distribution pattern. In the WET, a 280 values were generally low while S 275–295 values were generally high. Vertical distributions of a 280 and S 275–295 also varied in different regions. Terrestrial input, phytoplankton production, sediment release or photobleaching may be responsible for the dynamics of CDOM. Relationships among CDOM related parameters could partly support this conclusion. a 280 were also used to trace different water masses and the result showed that the influence of Changjiang Diluted Water could reach the outer shelf of the northern ECS, and that the Kuroshio Current had a strong influence on the middle shelf of the southern ECS. [ABSTRACT FROM AUTHOR]

Concentrations of particulate organic carbon (POC) and total hydrolyzable amino sugars (THAS) were measured along a transect of the dynamic South Yellow Sea (SYS) to investigate the bioreactivity and bacterial reworking of particulate organic matter (POM). Results showed that POM bioavailability was linked with primary production, as revealed by the significant correlation between chlorophyll- a concentrations and the diagenetic indicator glucosamine/galactosamine (GlcN/GalN). Production of bioavailable POM could rapidly stimulate microbial activity, generating hot spots of heterotrophic alteration. Lower GlcN/GalN ratios (<3) observed in the entire SYS indicate that POM underwent extensive microbial alteration. In particular, extremely low GlcN/GalN ratios (∼0.7) were found in the Yellow Sea Cold Water Mass, reflecting high bacterial alteration of POM. Estimates based on the bacterial biomarker muramic acid showed that on average ∼13% of POM in the SYS was of bacterial origin. Elevated bacterial contributions were found in both nearshore and offshore areas. Strong mixing in the nearshore and the presence of cyclonic eddies in offshore waters may increase the residence time of POM in the water column and thus promote bacterial transformation of POM. Overall, our findings indicate that bacterial reworking of POM varies with productivity and that the extensive bacterial transformation of the remaining POM observed in the water column probably enhances long-term carbon sequestration. [ABSTRACT FROM AUTHOR]

Background metal concentrations are important in assessing pollution level of marine sediments; however, they can be significantly altered by local depositional environments, resulting in significant errors in regional pollution assessment. This study was based on the investigation of the background levels of heavy metals in the Bohai Sea sediments using sediment core, 2-sigma outlier, and regression methods. We also estimate the ecological risks of heavy metals for surface sediments collected from the Bohai Sea using the three methods mentioned above. Ecological risks of heavy metals calculated using the regression method show wide disparities and significant differences from those calculated using the sediment core and 2-sigma methods, indicating that the regression method is not suitable for the Bohai Sea, likely as a result of its complex sources. Conversely, the estimated ecological risks using the sediment core method are moderate, and most heavy metals, except for Hg and Cd, have negligible contamination. • Regional metal (Fig. 1) backgrounds in the semi-closed Bohai Sea sediments are determined. • Three methods are used to determine metal backgrounds. • Regression is not suitable to determine metal backgrounds of Bohai Sea sediments. • Pollution levels of Bohai Sea sediments may be overestimated in previous studies. [ABSTRACT FROM AUTHOR]

Transform faults in back-arc basins are the key to revealing the evolution of marginal seas. Four marginal basins in the Western Pacific, i.e. the South China Sea (SCS), Okinawa Trough (OT), West Philippine Basin (WPB) and Shikoku-Parece Vela Basin (SPVB), were studied to redefine the strikes and spatial distribution of transform faults or fracture zones. Based on high-resolution tectonomorphology, gravity and magnetic anomalies, pattern of magnetic lineations, seismic profiles, geometry of basins and palaeomagnetic data, together with analyses of regional geological setting, plate reconstruction and geodynamic analysis, this paper suggests that all the transform faults in the four marginal basins are in general NNE-trending. Moreover, by comparing with the contemporary structural framework of the East Asian Continental Margin, we propose new models concerning marginal seas spreading and have revised the previous Cenozoic plate reconstruction models related to the East Asian Continental Margin and the Western Pacific marginal seas. There are three possible origins of these NNE-trending transform faults. 1. Inheriting the orientation of the strike-slip faults at the rifting continental margin (e.g. the SCS and OT). The real strike of transform faults should not be NW but NNE. The large-scale NNE-trending dextral strike-slip faults distributed in the continental shelf of the SCS control a series of pull-apart basins of the SCS. Due to a higher degree of pull-apart, oceanic crust began to open. Then they evolved into the NNE-trending transform faults in the SCS and could also be regarded as a natural extension of the NNE-trending strike-slip faults in the South China Block (SCB). The geodynamic mechanism of the OT is similar to that of the SCS. Consequently, transform faults of the OT should also be NNE-trending, which is not perpendicular to the spreading axis but instead displays oblique spreading. 2. Izu-Bonin-Mariana (IBM) Trench retreat to the NNE and NE. Subduction rollback to the NE and NNE produced the NE- and NNE-striking horizontal tensile stress, resulting in the rifting of the Kyushu-Palau Ridge (KPR), controlling the spreading of the SPVB and forming the NE- and NNE-trending transform faults. This also involves oblique spreading. 3. The later overall rotation of the Philippine Sea Plate (PSP). Since 25 Ma, the WPB has rotated clockwise about 40°. Therefore the NW- and NNW-trending transform faults that formed at the later spreading stage have rotated to be the near-N-S- or NNE-striking faults. These transform faults are almost perpendicular to the spreading axis. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Ecological evidence suggests that heterotrophic diazotrophs fueled by organic carbon respiration in sediments play an important role in marine nitrogen fixation. However, fundamental knowledge about the identities, abundance, diversity, biogeography, and controlling environmental factors of nitrogen-fixing communities in open ocean sediments is still elusive. Surprisingly, little is known also about nitrogen-fixing communities in sediments of the more research-accessible marginal seas. Here we report on an investigation of the environmental geochemistry and putative diazotrophic microbiota in the sediments of Bohai Sea, an eutrophic marginal sea of the western Pacific Ocean. Diverse and abundant nifH gene sequences were identified and sulfate-reducing bacteria (SRB) were found to be the dominant putative nitrogen-fixing microbes. Community statistical analyses suggested bottom water temperature, bottom water chlorophyll a content (or the covarying turbidity) and sediment porewater Eh (or the covarying pH) as the most significant environmental factors controlling the structure and spatial distribution of the putative diazotrophic communities, while sediment Hg content, sulfide content, and porewater SiO2-3-Si content were identified as the key 3 environmental factors correlated positively with the nifH gene abundance in Bohai Sea sediments. Comparative analyses between the Bohai Sea and the northern South China Sea (nSCS) identified a significant composition difference of the putative diazotrophic communities in sediments between the shallow-water (estuarine and nearshore) and deep-water (offshore and deep-sea) environments, and sediment porewater dissolved oxygen content, water depth and in situ temperature as the key environmental factors tentatively controlling the species composition, community structure, and spatial distribution of the marginal sea sediment nifH-harboring microbiota. This confirms the ecophysiological specialization and niche differentiation between the shallow-water and deep-water sediment diazotrophic communities and suggests that the in situ physical and geochemical conditions play a more important role than geographical contiguity in determining the community similarity of the diazotrophic microbiota in marginal sea sediments. [ABSTRACT FROM AUTHOR]

Based upon 21 field surveys conducted from March 2011 to November 2013, monthly variation of carbon dioxide partial pressure ( p CO 2 ) and other carbon system parameters were investigated for the first time (to our knowledge) at A4HDYD station (38°40′N, 122°10′E) located in the North Yellow Sea, a region with a seasonal thermocline. Surface p CO 2 was undersaturated from March to May and nearly in equilibrium with the atmosphere from June to August. During September and November, p CO 2 declined to a lower level than that from June to August, but reached the highest level in December. In contrast, p CO 2 declined to atmospheric CO 2 levels in February. Overall, the study area was a net CO 2 sink at a rate of 0.85 ± 0.59 mol C m − 2 yr − 1 . The underlying processes governing the variation of p CO 2 were also examined. In general, temperature had an important influence on the monthly variation of p CO 2 , but its effect was counterbalanced by biological production in spring and vertical mixing in early winter. Our study indicated that dynamic mechanism studies based on high temporal resolution observations are urgently needed to understand the complexity of the carbon cycle and detect biogeochemical changes or ecosystem responses to climate change on continental margins. [ABSTRACT FROM AUTHOR]

The concentration and geochemical fractionation of six trace metals related with environmental quality assessment, namely Cd, Cr, Cu, Ni, Pb, and Zn, in 30 surface sediments from both inshore and offshore areas of the Taiwan Strait were measured to investigate their distribution characteristics, evaluate their potential mobility, and assess their pollution status. The geoaccumulation index results indicated that, on average, the studied metals presented an order of Cd > Pb > Ni > Zn > Cu > Cr and were practically in uncontaminated status except Cd. The results of the sequential extraction analysis indicated that, on average, the studied metals were mostly accumulated in residual fraction except Cd whose concentration was the highest in the acid soluble fraction presenting a high risk to the environment, and their mobility decreased in the sequence of Cd > Pb > Ni > Cu > Zn > Cr. Based on the mean probable effect level quotients, the combination of the studied metals had an 8 % probability of being toxic at two sampling sites and had a 21 % probability of being toxic at the rest of sites. The spatial distribution of the studied metals in total concentrations and different geochemical fractions corroborated the previous findings about the possible sediment transportation routes in and around the Taiwan Strait. [ABSTRACT FROM AUTHOR]

Biogeographic boundaries constraining species' distributions often generate intraspecific ‘breaks’ for those species whose ranges span them—known as the ‘biogeography-phylogeography concordance’ hypothesis. The East China Sea (ECS) in the northwestern Pacific comprises two reported boundaries: the Shandong Peninsula and the Changjiang Estuary, providing an elegant setting to test the hypothesis in marine environment. Here we investigated population structure of the surf clam Mactra veneriformis (Reeve, 1854) using 235 individuals from its major distribution in the ECS, represented by mitochondrial cytochrome oxidase I sequences. A ‘star-like’ topology with shallow divergence was revealed for all haplotypes, of which the central (also assumed ancestral) one appearing in all populations. No significant genetic structure was revealed among populations, suggesting substantial genetic homogeneity across the range. Demographic expansion was revealed for individual and overall populations, and the expansion time was estimated from 23,000 years ago. These results suggested that the M. veneriformis populations originated from an ancestral panmictic population in the ECS basin, and had experienced significant population expansion since the last glacial maximum. From a mitochondrial view, the two boundaries did not act as barriers for the phylogeography of M. veneriformis . [ABSTRACT FROM AUTHOR]

The distributions of dissolved inorganic carbon ( C T ), total alkalinity ( A T ) and pH at 25 °C (pH 25 ) were determined in the Northern South China Sea Shelf-sea (NoSoCS) in early June, 2010 during a low flow period. The distributions of the partial pressure of CO 2 ( p CO 2 ), in situ pH, and temperature normalized p CO 2 (N p CO 2 ) were derived from the measured values. The distribution of A T is linearly related to salinity indicating that its distribution is controlled primarily by mixing between the surface water and the subsurface North Pacific Tropical Water. Aside from physical mixing, the distribution of C T is also influenced by its loss through biological uptake and CO 2 evasion to the atmosphere. The net community production (NCP) rate in the NoSoCS is estimated to be 10±20 (with a range of 4–13) mmol C m −2 d −1 . Within the NoSoCS, the NCP is elevated in the coastal upwelling area, where it is estimated to reach 30±17 mmol C m −2 d −1 . In addition to temperature, upwelling and biological uptake also affect the distribution of the surface p CO 2 and in situ pH. The waters in the NoSoCS are super-saturated with respect to aragonite at all depths as the saturation horizon is at 600–800 m in the open northern South China Sea. Nevertheless, the aragonite saturation state, Ω Ar , in the surface water, which is mostly between 3.3 and 3.5, is already within the range that has been suggested as barely adequate to marginal for the growth of the tropical shallow-water corals. The Ω Ar is linearly related to in situ pH. At the reported rate of pH decrease in the oceans as a result of ocean acidification, Ω Ar might reach a value that is considered “extremely marginal” within several decades and the existence of this type of coral reef ecosystem in the NoSoCS may then be threatened. [ABSTRACT FROM AUTHOR]

The hydrographic characteristics and the distributions of nitrate+nitrite, or (N+N), and soluble reactive phosphate, or SRP, in the No rthern So uth C hina Sea S helf-sea (NoSoCS) were determined in four transects across the shelf in the summer of 2010 and in two transects in the winter of 2011. The NoSoCS may be sub-divided into the inner shelf, the middle shelf and the outer shelf at water depths of <40 m, 40–90 m and 90–120 m, respectively. The water in the inner shelf is colder and its concentrations in the nutrients and chlorophyll-a (Chl_ a ) are higher in both seasons while the water in the outer shelf is warmer and its concentrations are lower. With depth, since the mixed layer depth in the NoSoCS in the winter (~70 m) and in the summer (~40 m) are both shallower than the shelf break depth (~120 m), the colder and relatively nutrient-rich upper thermocline-upper nutricline water in the open South China Sea (SCS) can freely extend into the NoSoCS to become its bottom water. This is a distinguishing characteristic of the NoSoCS as, unlike many of the more extensively studied temperate shelf-seas, vertical mixing within the NoSoCS, rather than shelf-edge processes such as upwelling, is the primary mechanism for bringing the nutrients from the sub-surface in the adjoining northern SCS to its mixed layer for supporting primary production. Four processes that may contribute to this vertical mixing in the NoSoCS include: shelf-wide winter surface cooling and convective mixing; the actions of internal waves which probably occur in both seasons along the entire outer shelf; wind and topographically induced coastal upwelling in the summer off Shantou at the northwestern corner of the NoSoCS; and winter formation of bottom water at the outer portion of the inner shelf and the inner portion of the middle shelf. The density of this bottom water formed in the winter of 2011 was equivalent to the density at ~120 m in the open SCS so that it could cascade across the shelf and contribute to not only vertical mixing but also in cross shelf mixing and the ventilation of the upper thermocline and nutricline of the open SCS. An enrichment in (N+N) over SRP, where (N+N)/SRP exceeded the Redfield ratio of 16 and [N+N] ex >0, was found when salinity dropped below about 33. In these fresher waters, which were found exclusively in the inner shelf during this study, SRP potentially could become the limiting nutrient. [ABSTRACT FROM AUTHOR]