Search

Sea-level rise (SLR) has become a serious global threat resulting from the climate change. The global rate of SLR observed by the long records of satellite altimeters (1993–2011) is at 3.11 mm/yr with the mean rate at Southeast Asia (SEA) slightly higher at 3.9 mm/yr (1993–2009). Many countries in SEA face the risk of SLR highlighting the flood dangers. In addition to the land prone to sinking, several countries like Indonesia face extreme SLR events. To provide an understanding of the SLR rates in SEA, this paper answers several questions associated with SLR in SEA. What are the factors that contributed to the SLR on regional scales? How can the SLR be mathematically modelled? How much has the sea level increased over the past decades based on the observed tide gauge, radar altimeters and data assimilation techniques? SLR from these techniques is reviewed because they provide the complete spectrum of processes that lead to sea-level variability. Finally, the prospects for future research are summarized in order to provide guidance for the future SLR studies. [ABSTRACT FROM AUTHOR]

When regional (limited-area) models of the hydrodynamics of the atmosphere and ocean are run over an extended time, variability unrelated to external "drivers" emerges: this variability is colloquially named "hydrodynamical noise" or just "noise". This article summarises what we have learned in the past few years about the properties of such noise and its implications for numerical experimentation and analysis. The presence of this noise can be identified easily in ensembles of numerical simulations, and it turns out that the intensity of the noise is closely linked to scale-dependent "memory". The "memory" in the atmosphere and ocean describes the persistence of atmospheric and oceanic conditions, usually quantified by an autocorrelation function. At the system level, this "memory" term, as given by Hasselmann's stochastic climate model, plays a key role. In the case of marginal seas, the process of baroclinic instability modulated by tides and the formation of seasonal thermoclines are significant aspects. Some more general aspects are discussed, such as the applicability of the stochastic climate model to systems outside of atmospheric and oceanic dynamics, for example, biogeochemical systems, the irreversibility of tipping points, the challenges of detecting changes beyond a noise level, and the attribution of causes of change. [ABSTRACT FROM AUTHOR]

Sr-Nd isotopes are widely utilized as reliable tracers in sediment provenance studies. In this study, we compiled 304 Sr and 335 Nd isotope data of fine-grained surface sediments collected from major rivers in eastern China, including the Huanghe River, Changjiang River, southeastern coastal rivers, and rivers in Taiwan Island, as well as from marginal seas (Yellow Sea and East China Sea) and the Okinawa Trough. This comprehensive dataset allowed us to examine the spatial distribution patterns of these isotopes and their implications for provenance analysis. The variations of εNd values in the sediments in Changjiang and Huanghe Basins primarily reflect the diversity of sediment sources, whereas the 87Sr/86Sr ratios are influenced by both grain size and source provenance. Moreover, the reduction in 87Sr/86Sr ratios observed in the middle and lower Changjiang River is attributed to the inputs of sources characterized by distinct 87Sr/86Sr signatures beyond mere grain size effects. In the southeastern coastal and Taiwan rivers, sediments in the tidal reaches of the Jiao River exhibit hybrid characteristics, a mix of Changjiang-derived sediment and those originating from local catchments. Conversely, the Min River and Jiulong River sediments predominantly reflect local sources, with minimal influence from the Changjiang River. The significant isotopic variation of Sr-Nd isotopic characteristics observed between riverine sediments on the eastern and western sides of Taiwan Island underscores the diverse provenance heterogeneity of source rocks in the region. For the marginal seas, our data indicates that the surface sediments in the central mud area of the South Yellow Sea and the southern Yellow Sea are predominantly sourced from the Changjiang River catchment, potentially augmented by inputs from Korean rivers. The inner shelf sediments of the East China Sea are primarily influenced by Changjiang River inputs, whereas rivers in eastern Taiwan Island contribute to the sediments on the middle and outer shelves. Overall, the sediment Sr-Nd isotopic characteristics from the principal sources entering the eastern China marginal seas exhibit considerable similarity, presenting a substantial challenge for quantifying individual river end-member contributions based solely on the Sr-Nd isotopic signatures. To enhance the precision of quantitative assessments in sediment source-to-sink processes, it is imperative to define a narrower range of Sr-Nd isotopic signatures for potential end-members and to expand Sr-Nd isotopic investigations in these marginal seas, with a particular emphasis on regions beyond the current scope of investigations (such as mud areas). [ABSTRACT FROM AUTHOR]

The South China Sea is a typical marginal sea characterized by the presence of numerous seamounts. However, the effect of seamounts on the air‐sea CO2 flux has not yet been well studied. In September 2021, the air‐sea CO2 flux was measured directly using eddy covariance (EC), and discrete waterside sampling was conducted. The results indicate that the northern South China Sea is a source of atmospheric CO2. Furthermore, EC measurements show that the seamount emits CO2 at an average rate of 0.34 mmol m−2 hr−1, nearly double that of non‐seamount areas. We suggest that the upwelling around the seamount transports deep water rich in dissolved inorganic carbon to the upper ocean, increasing the partial pressure of CO2 there. In addition, the increase in nutrients caused by the upwelling would increase the concentration of chlorophyll‐a, resulting in a productive area that emits CO2. Plain Language Summary: The South China Sea (SCS) serves as a minor CO2 source, and the air‐sea CO2 flux in its northern region demonstrates challenging spatiotemporal variations. In our investigation, we conducted underway assessments in the northern SCS and validated its emission of CO2, particularly in the vicinity of seamount ocean zones. CO2 emissions may have been intensified by the upward movement of seawater surrounding the seamount region. Key Points: The northern South China Sea emitted CO2 into the atmosphere at a mean rate of 0.28 mmol m−2 hr−1 in September 2021The CO2 flux almost doubled as the seamount was approached, indicating an increase in CO2 emissions near the seamountUpwelling releases high dissolved inorganic carbon, which increases the partial pressure of CO2 on the sea surface around the seamount [ABSTRACT FROM AUTHOR]

The Sulu Sea is a small marginal sea in the western Pacific, but it is a very complex and tectonically active region, situated amidst the convergence of the Eurasian, Pacific, and India-Australian plates. Deciphering its geodynamic evolution is crucial, but our understanding of its opening, closure, and tectonic history remains inadequate. The main aim of this study was to systematically study the opening and subsequent closure of the Sulu Sea though discerning tectonic unconformities, structural features, and subduction-collision tectonic zones around margins of the sea. The interpreted sections and gravity anomaly data indicate that the NE Sulu Sea has undergone Neogene extension and contraction due to subduction and collision along the northern margins of the Sulu Sea, whereas the SE Sulu Sea gradually extended from northwest to southeast during the Middle Miocene and has subsequently subducted since the Middle Miocene along the southeastern margins of the Sulu Sea. Several subduction and collision boundaries with different characteristics were developed including continent-continent collision, arc-continent collision, and ocean-arc subduction. The different margins of the Sulu Sea showed distinct asynchronous subduction and collision processes. The northern margins of the Sulu Sea can be divided into three subduction-collision tectonic zones from west to east: the Sabah-Nansha block collision has occurred in NE Borneo since the Early Miocene, followed by the SW Palawan-Cagayan arc collision in SW Palawan Island since the Middle Miocene, and the NW Palawan-Mindoro arc collision since the Late Miocene with further oblique subduction of the Philippine Sea Plate. The southeastern margins can also be divided into two subduction tectonic zones from south to east: the SE Sulu Sea has subducted southward beneath the Celebes Sea since the Middle Miocene, followed by the southeastward subduction beneath the Philippine Sea Plate since the Pliocene. Since the Miocene, the interactions among the Australia-India, the Philippine Sea, and the Eurasian plates have formed the circum-Sulu Sea subduction-collisional margins characterized by microplate collisions, deep-sea trough development, and thick sediments filling in the orogenic foreland. This study is significant for gaining insights into the opening and closure of marginal seas and the dynamics of multiple microplates in Southeast Asia. [ABSTRACT FROM AUTHOR]

In this work, the seasonal variations of the carbonate system and air‐sea CO2 fluxes were investigated by two cruises in the southern Yellow Sea (SYS) and the East China Sea (ECS), which were significantly influenced by the Changjiang riverine inputs across seasons. Biological‐mediated change of dissolved inorganic carbon (DIC) was first quantitated through a three end‐member mixing model from winter to spring. Our modeling results suggested that DIC addition through biological remineralization persisted in the SYS during winter and spring, while DIC removal was evident in the Changjiang River Plume and the offshore ECS triggered by river inputs in spring. Horizontal and vertical mixing together constituted the largest contribution to the interseasonal variability of partial pressure of CO2 (pCO2) in the SYS (−69.5%), the river plume (−59.3%), and the ECS offshore (−43.8%), followed by temperature effects in the plume area (29.4%), and biological processes in the ECS offshore (24.1%) and the SYS (−7.7%), with air‐sea CO2 exchange contributing the least in both three subregions. The SYS, the river plume, and the ECS offshore all acted as atmospheric CO2 sinks in both winter and spring. Furthermore, their ability to absorb atmospheric CO2 increased from winter to spring, as reflected in a ∼1.8‐fold increase in the overall spring air‐sea CO2 flux compared to winter estimation. Plain Language Summary: The carbonate system has played an essential role in regulating the ocean carbon cycle due to its buffer capacity for ocean acidification, especially in continental shelf seas. However, complex biological and physical processes present difficulties in assessing the seasonal dynamics of the carbonate system and following air‐sea CO2 fluxes. In this study, seasonal variations of the carbonate system were identified in the southern Yellow Sea (SYS) and the East China Sea (ECS). From winter to spring, biological DIC addition happened in the SYS, while DIC removal by biological production exceeded the addition by remineralization and caused most springtime DIC consumption in the river plume and the ECS offshore. We also quantified pCO2 variations from winter to spring, revealing the importance of physical mixing in controlling the ocean carbon cycle. Our study regions acted as atmospheric CO2 sinks in winter and spring, and their sink capacity was strengthened from winter to spring. Key Points: Dissolved inorganic carbon (DIC) addition occurred in the southern Yellow Sea (SYS) during winter and spring, while springtime DIC removal occurred in the river plume and the East China Sea (ECS) offshorePhysical mixing became the primary factor in regulating the interseasonal variation of pCO2The capacity of coastal waters in absorbing atmospheric CO2 was enhanced from winter to spring [ABSTRACT FROM AUTHOR]

Semi‐enclosed seas are often associated with elevated local threats and distinct biogeographic patterns among marine fishes, but our understanding of how fish assemblage dynamics vary in relation to relatively small semi‐enclosed seas (e.g., the Gulf of Aqaba) remains limited. Baited remote underwater video surveys (n = 111) were conducted across ~300 km of coral reef habitats in the Gulf of Aqaba and the northern Red Sea. A total of 55 predatory fish species were detected, with less than half of all species (n = 23) observed in both basins. Relative abundance patterns between the Gulf of Aqaba and the northern Red Sea were variable among taxa, but nearly twice as many predatory fish were observed per unit of effort in the northern Red Sea. In general, assemblages in both basins were dominated by three taxa (Epinephelinae, Carangidae, and Lethrinidae). Large‐bodied and threatened species were recorded at very low abundances. Multivariate analysis revealed distinct assemblage structuring of coral reef predators between the Gulf of Aqaba and the northern Red Sea. Most of the species driving these differences were recorded in both basins, but occurred at varying levels of abundance. Environmental factors were largely unsuccessful in explaining variation in assemblage structuring. These findings indicate that biological assemblages in the Gulf of Aqaba are more distinct than previously reported and that reef fish assemblage structuring can occur even within a relatively small semi‐enclosed sea. Despite inter‐basin assemblage structuring, the overall low abundance of vulnerable fish species is suggestive of overexploitation in both the Gulf of Aqaba and the northern Red Sea of Saudi Arabia. As the region surveyed is currently undergoing large‐scale coastal development, the results presented herein aim to guide spatial management and recovery plans for these coral reef systems in relation to this development. [ABSTRACT FROM AUTHOR]

Deep-sea habitats are currently recognized as a hot spot for mercury (Hg) accumulation from anthropogenic sources, resulting in elevated concentrations of total mercury (THg) in deep-sea megafauna. Among them, deep-sea sharks (Class Chondrichthyes) are characterized by high trophic position and extended longevity and are, therefore, at high risk for mercury contamination. Despite this, sharks are overexploited by fishing activity in increasingly deeper water, worldwide, imposing health risks to human consumption. While it is imperative to better understand long-term mercury contamination in deep-sea megafauna, few historical data sets exist to capture this process. Here we explore four decades (1985–2022) of THg accumulation in five species of deep-sea sharks (G. melastomus, E. spinax, S. rostratus, C. granulosus, and D. licha) of the ultra-oligotrophic Southeastern Mediterranean Sea (SEMS) sampled during 19 research cruises. We exhibited exceptionally high THg levels (per length/weight), the highest as 16.6 μg g−1 (wet wt.), almost entirely (98.9 %; n = 298 specimens) exceeding the limit for safe consumption (0.3–0.5 μg THg g−1 wet wt.). The maximal THg levels of the long-lived species D. licha and C. granulosus in the SEMS were enriched by a factor of ∼ 7 and >10 compared to counterpart species from other oceanic areas, respectively. We attribute this to the ultra-oligotrophic conditions of the SEMS, which cause slower growth rates and dwarfism in deep-sea sharks, resulting in an extended exposure time to mercury contamination. In the long-lived species, C. granulosus and D. licha, a temporal increase of average THg levels of ∼ 80 % was recorded between 1987–1999 and 2021–2022. This likely reflects the long-term accumulation of historical anthropogenic Hg in deep-sea environments, which is further amplified in marginal seas such as the Mediterranean, impacted by global air pollution crossroads and surrounded by land-based pollution sources. Future consumption of products from deep-sea sharks is potentially high risk to human health.

The Sulu Sea is a small marginal sea in the western Pacific, but it is a very complex and tectonically active region, situated amidst the convergence of the Eurasian, Pacific, and India-Australian plates. Deciphering its geodynamic evolution is crucial, but our understanding of its opening, closure, and tectonic history remains inadequate. The main aim of this study was to systematically study the opening and subsequent closure of the Sulu Sea though discerning tectonic unconformities, structural features, and subduction-collision tectonic zones around margins of the sea. The interpreted sections and gravity anomaly data indicate that the NE Sulu Sea has undergone Neogene extension and contraction due to subduction and collision along the northern margins of the Sulu Sea, whereas the SE Sulu Sea gradually extended from northwest to southeast during the Middle Miocene and has subsequently subducted since the Middle Miocene along the southeastern margins of the Sulu Sea. Several subduction and collision boundaries with different characteristics were developed including continent-continent collision, arc-continent collision, and ocean-arc subduction. The different margins of the Sulu Sea showed distinct asynchronous subduction and collision processes. The northern margins of the Sulu Sea can be divided into three subduction-collision tectonic zones from west to east: the Sabah-Nansha block collision has occurred in NE Borneo since the Early Miocene, followed by the SW Palawan-Cagayan arc collision in SW Palawan Island since the Middle Miocene, and the NW Palawan-Mindoro arc collision since the Late Miocene with further oblique subduction of the Philippine Sea Plate. The southeastern margins can also be divided into two subduction tectonic zones from south to east: the SE Sulu Sea has subducted southward beneath the Celebes Sea since the Middle Miocene, followed by the southeastward subduction beneath the Philippine Sea Plate since the Pliocene. Since the Miocene, the interactions among the Australia-India, the Philippine Sea, and the Eurasian plates have formed the circum-Sulu Sea subduction-collisional margins characterized by microplate collisions, deep-sea trough development, and thick sediments filling in the orogenic foreland. This study is significant for gaining insights into the opening and closure of marginal seas and the dynamics of multiple microplates in Southeast Asia.

This study examines and compares 3D distributions of crustal and upper mantle density contrast with a set of geological and geophysical data for the heads of six plumes (Yellowstone, Emeishan, Cathaysia, Sea-of-Okhotsk, Maya–Selemdzha, and Indigirka–Kolyma plumes) down to 200 km depth. According to our data, the asthenospheric parts of the plumes have mushroom shapes, while the asthenospheric magmas are spreading out beneath the lithosphere bottom, less frequently beneath the crustal bottom. The plume heads become narrower at distances of 250–300 km from the central conduit to decrease to diameters of 200–300 km at depths of 100–120 km. In most of the cases, the plume lithospheric and crustal fragments are convex toward the ground surface. The uplifts are occasionally complicated with local depressions in the upper crust, which can be explained by subsidence of the domes of the structures above magma chambers in the subcrustal viscous layer and asthenosphere. Plumes are frequently associated with zones of lithosphere tension (rifts), resulting in linear zones of lower viscosity being mapped in the lower lithospheric and crustal cross sections of the plumes. The structural settings of the plumes under consideration here are controlled by boundaries of lithosphere plates and large segments of the second order. The identity of geometry and rheology in the plumes that were formed at different times (Triassic to Neogene), and in regions far removed from each other (Northeast Russia, Amur region, northwestern United States, South China, and Sea of Okhotsk), provide evidence of the universality of the tectonic settings that favor the penetration of mantle flows into the upper tectonic shells of the Earth. The foremost among these are tension zones in the lithosphere, especially areas where differently directed lithospheric faults intersect. [ABSTRACT FROM AUTHOR]

The marginal seas are in the transition zone between land and ocean and are often subject to extensive human activities causing multiple stresses on the marine environment and its ecosystems. A large gap between our scientific knowledge and our treatment of the sea illustrates a weak coupling between facts and values. The aim of this work is to initiate a discussion of how to improve the human relationship with the sea. Research into the UN 2030 Agenda with its ambition to transform our world into a sustainable and healthy physical and mental environment creates an opportunity to deepen our understanding of human behaviour and values and how they impinge on the physical world. Together with improved communication and transdisciplinary initiatives, these efforts should be vital in better understanding the marginal sea system and generating a new relationship with the ocean.There is a pressing need to change the human relationship with the ocean and its marginal seas. Connecting the natural and human sciences can improve our awareness of the sea's state and support behavioural change. Such transdisciplinary development requires training in broad thinking and communication. It is time for natural science to “open the human black box”, adding values to facts.

After Bakun proposed his hypothesis in 1990 regarding upwelling under climate change, researchers conducted intensive studies to obtain the trends, current status, and future predictions of upwelling. Numerous studies have mainly focused on four major upwelling areas, which are part of the Eastern Boundary Upwelling System (EBUS). However, despite its importance, little attention has been given to the marginal seas upwelling areas such as the South China Sea (SCS), Arabian Sea, Baltic Sea, and other small-scale upwelling locations. Here, we combined several published studies to develop a new synthesis describing climate change impacts on these areas. There had been uncertainty regarding the intensification of upwelling, depending on the locations, data type, and method used. For the SCS, Vietnam and the northern SCS showed intensifying upwelling trends, while the Taiwan Strait showed a decreasing trend. Separate studies in eastern Hainan and the Arabian Sea (Somali and Oman) showed contrasting results, where both increasing and decreasing trends of upwelling had been recorded. Like the SCS, the Baltic Sea showed different results for different areas as they found negative trends along the Polish, Latvian and Estonian, and positive trends along the Swedish coast of the Baltic Sea and the Finnish coast of the Gulf of Finland. While small scales upwelling in La Guajira and southern Java showed increasing and decreasing trends, respectively. All of these limited studies suggest that researchers need to conduct a lot more studies, including the future projection of upwelling, by using climate models to develop a new understanding of how the upwelling in the SCS responds to climate change. [ABSTRACT FROM AUTHOR]

Dissolved organic carbon (DOC) and the optical properties of dissolved organic matter (chromophoric- and fluorescent dissolved organic matter; CDOM and FDOM) were measured to determine the distributions and drivers of DOM in the northwestern Pacific marginal seas, including the East China Sea, the Yellow Sea, and the East/Japan Sea, in August 2020. In this study, the concentrations of DOC and CDOM/FDOM in surface water showed good correlations with salinity, indicating a predominant contribution from the Changjiang River. However, significantly high concentrations of DOC and FDOM were also observed in the central Yellow Sea region, which seems to be produced mainly from the continental shelf-water and enriched over the water residence time of the Yellow Sea, while the lowest concentrations of DOC and CDOM/FDOM were found in high-salinity waters near the southern sea of Korea. In addition, the East/Japan Sea showed relatively low DOC concentrations and high FDOM values. To distinguish the physical mixing and biogeochemical processes of DOM, we estimated the water mass fractions using an optimum multi-parameter analysis with hydrological and DOM parameters of the major water masses in this region. Our results showed that five primary external drivers of DOM distribution were intrusions of (1) the Changjiang diluted water and (2) the Kuroshio Current water in the surface water, the mixing of (3) the Yellow Sea bottom cold water and (4) the Kuroshio sub-surface water in the bottom layer, and (5) upwelling of the East/Japan Sea water. We conclude that the distribution of DOM is significantly influenced by the mixing of multiple water masses, and the optical signature of DOM can be an effective proxy for tracing the origins and characteristics of DOM in this region.

During the past century, several extreme summer floods in Central Europe were associated with so-called Vb-cyclones propagating from the Mediterranean Sea north-eastward to Central Europe. The processes intensifying the precipitation in synoptic situations with Vb-cyclones in the Danube, Elbe, and Odra catchments are only partially understood. Our study aims to investigate these processes with Lagrangian moisture-source diagnostics for 16 selected Vb-events. Moreover, we analyse the characteristics of typical moisture source regions during 1107 Vb-events from 1901 to 2010 based on ERA-20C reanalysis dynamically downscaled with COSMO-CLM+NEMO. We observe moisture contributions by various source regions highlighting the complex dynamical interplay of different air masses leading to moisture convergence in synoptic situations with Vb-cyclones. Overall, up to 80% of the precipitation originates from the European continent, indicating the importance of continental moisture recycling, especially within the respective river catchment. Other major moisture uptake regions are the North Sea, the Baltic Sea, the North Atlantic, and for a few events the Black Sea. Remarkably, anomalies in these oceanic source regions show no connection to precipitation amounts in synoptic situations with Vb-cyclones. In contrast, the Vb-cyclones with the highest precipitation are associated with anomalously high evaporation in the Mediterranean Sea, even though the Mediterranean Sea is only a minor moisture source region on average. Interestingly, the evaporation anomalies are not connected with sea-surface temperature but with wind-speed anomalies (Spearman's rank correlation coefficient R ≈ 0.7, significant with p < 0.01 ) indicating mainly dynamically driven evaporation. The particular role of the Mediterranean Sea hints towards possible importance of Mediterranean moisture for the early-stage intensification of Vb-cyclones and the pre-moistening of the continental uptake regions upstream of the target catchments. [ABSTRACT FROM AUTHOR]

Cross-shelf exchanges in the Black Sea were investigated using remote sensing data and an ocean circulation model to which an eddy-tracking algorithm and Lagrangian particle tracking model was applied. An anticyclonic eddy in 1998 and a cyclonic eddy in 2000 were investigated in detail. Eddy-induced cross-shelf transport of low salinity and high Chl-a waters reached a maximum in the presence of filaments associated with these eddies. The daily mean volume transport by the eddies was comparable with the previously documented transport by eddies of similar size in the north-western shelf region. Lagrangian particle tracking results showed that 59% of particles initially released over the shelf were transported offshore within 30 days by the 1998 anticyclone and 27% by the 2000 cyclone. The net volume transport across the Black Sea shelf-break reached the maxima in winter, coinciding with the increase in wind stress curl and mean kinetic energy that is a measure of the intensity of the boundary current. Ekman transport directly influences the cross-shelf exchanges in the surface layer. The south-eastern Black Sea is presented as an important area for cross-shelf transport. The total cross-shelf transport can be divided into its "large-scale" and "eddy-induced" components. Eddy-induced transport was 34% and 37% of the total cross-shelf transport (1998–2014) in the Black Sea in the off-shelf and on-shelf directions, respectively, but these values ranged between 25% and 65% depending on the eddy activity over time. [ABSTRACT FROM AUTHOR]

A spatial distribution of methane dissolved in sea water is a critical but poorly understood factor in the context of seismic activity. Based on the results of the RV AKADEMIK OPARIN integrated geological-geophysical expedition (September 21 – October 31, 2017), this paper deals with the regularities of methane concentration variability in the surface layer of the Sea of Japan: the average growth and the average growth period were 70 % and 10 h, respectively, after each earthquake whereas a decrease in methane concentration in the sea water was 10–30 % 2–4 h before a seismic event. A decrease in methane concentration occurs irrespectively of the depth of an earthquake. The results obtained show good agreement with the published data and gaseous-geochemical monitoring materials, thus making it possible to associate seismic-related gaseous-geochemical regime not only with gas-saturated sediments but also with the water column of the Japan Basin (Sea of Japan).

• High-resolution coupled 226Ra and 228Ra mass balance model enables an SGD estimate. • SGD flux exceeds rivers by 3.4 times in large marginal seas. • Nutrient fluxes via SGD surpasses rivers and atmospheric deposition. • High N:P ratio SGD reveals the necessity in managing coastal groundwater quality. River and atmosphere are traditionally recognized as the primary nutrient sources impacting coastal ecosystems. Despite the increasing attention towards the often-neglected submarine groundwater discharge (SGD), its understanding and significance in highly human-impacted marginal seas remain limited. This study utilizes unprecedented high-resolution data (561 seawater and 282 groundwater radium samples) to provide precise estimates of 226Ra and 228Ra sources and sinks in the Eastern China Marginal Seas. A coupled 226Ra and 228Ra mass balance model enable an integrated SGD flux of (3.7 ± 2.4) × 1012 m3 yr−1, surpassing rivers by 3.4 times. Furthermore, nutrient delivery from SGD exceeds riverine and atmospheric inputs, potentially inducing substantial changes in coastal nutrient cycles. These alterations have profound implications for primary production and biological communities, deviating significantly from the Redfield ratio. Therefore, comprehending the significance of SGD in nutrient budgets is vital for a comprehensive understanding of biogeochemical dynamics and functionality of marginal sea ecosystems. [Display omitted] [ABSTRACT FROM AUTHOR]

Deep ocean regeneration of dissolved silica (DSi) is an essential part of the ocean silica cycle and is driven by a complex series of biogeochemical processes. Here we compare the distributions of DSi and other environmental parameters in several western Pacific marginal seas to explore the role of marginal seas in deep ocean DSi regeneration. Results show that in oligotrophic marginal seas (such as the South China Sea), the DSi content in deep waters is similar to that of the adjacent Pacific waters. However, in productive marginal seas (such as the Bering Sea), the DSi content in deep waters is markedly higher than that in adjacent Pacific waters at the same depths. This is mainly due to deep ocean DSi regeneration in the marginal sea basin, which is fueled by the high biogenic particle flux from the productive surface waters. On a global scale, deep ocean DSi regeneration is accelerated in productive marginal seas, causing marginal seas such as the Bering Sea to have the highest DSi concentrations of all global waters.

The East China Sea (ECS) lies on a wide shelf and embraces one of the world's largest rivers, Changjiang (Yangtze River), on the west and strong boundary current, Kuroshio, on the east, which can act as potentially huge sources of dissolved iron (dFe) to the overlying water. However, their magnitude, distribution, and transformation in the ECS are not yet well characterized. Here, we reported the results from the first large scale investigation of dFe concentrations in the water column from the ECS collected with an X‐Vane assemblage in August 2013. Samples from the Changjiang and other coastal rivers were also measured to constrain terrestrial fluxes. In surface waters, dFe concentrations show a strong gradient with patchy nature from the coast adjacent to the river mouth to the mainstream of the Kuroshio Current. The behavior of dFe in the ECS is closely linked to nutrient cycling and development of the sub‐surface chlorophyll maximum. Our dFe budget reveals that mass transport over the East China Sea Shelf (ECSS) is dominated by the input from the Taiwan Strait Warm Water, atmospheric deposition, and exchange with the open boundary current further offshore. The incursion of the Kuroshio Current across shelf break is a source of natural fertilization. The export of dFe from the ECSS nourishes other marginal seas (e.g., Japan Sea/East Sea) and the Kuroshio further downstream. Comparison with the literature data provides evidence that marginal seas play a critical role in bridging terrestrial and oceanic spheres in terms of Fe biogeochemistry. Key Points: Trace metal clean sampling techniques were applied in the investigation of dissolved iron (dFe) in the wide East China Sea (ECS)Multiple factors influencing dFe biogeochemistry in the ECS are discussed in this studyA dFe budget was constructed for the shelf area (<200 m) that emphasized the interaction between the boundary current and the shelf [ABSTRACT FROM AUTHOR]

On the basis of the mechanism of instability of the shear zone between moving lithospheric plates, a new version of the model for the formation of marginal seas of the Pacific Ocean in the form of successive occurrence of wave stresses and vortex structures has been proposed. The lithospheric plates in their lateral interaction zone possess to a great extent the properties of a viscous medium, where two tectonic masses with high but different viscosity and different densities weakly intermixing horizontally are moving at different velocities. Therefore, the interface begins to bend, resulting in vortex structures in the tectonosphere of marginal seas and adjacent continental areas. At sharp and rapid deformations, the Earth’s crust behaves like a solid body, and at long time deformations — like a viscous medium. This mechanism of formation of the seas reflects the initial stage of the collision of the Pacific plate with Eurasia, when the converging plates are just beginning to contact. Duplex zones are formed in the Earth’s crust and the upper mantle of marginal seas, where the crust-mantle substance is undergoing vortex circulation.

The effects of benthic dissolved organic carbon (DOC) flux on the dynamics of DOC in the deep continental margins (200 – 2000 m depth) is poorly understood. We investigated heterotrophic prokaryotes (hereafter bacteria) production (BP) and the bio-reactive properties of sediment-derived dissolved organic matter (SDOM) to elucidate microbially mediated cause-effect relationships regarding the rapid consumption of dissolved oxygen (DO) and accumulation of humic-like fluorescent DOM (FDOMH) in the deep-water column (750 – 2000 m depth range) of the Ulleung Basin (UB) in the East Sea. BP in the deep water (2.2 μmol C m-3 d-1) of the UB was among the highest reported for various deep-sea sites. The high DOC concentration (55 μM) likely supported the high BP seen in the deep-water column of the UB. Concentrations of DOC and C1 component of the FDOMH, which is indicative of microbial metabolic by-products, were 13-fold and 20-fold greater, respectively, in pore water than in the overlying bottom water, indicating that the sediment in the continental margins is a significant source of DOM in the overlying water column. Fine-scale water sampling revealed that BP near the sediment (0 – 30 m above the seafloor; 2.78 μmol C m-3 d-1) was 1.67 times higher than that measured in the water column above (30 – 100 m above the seafloor; 1.67 μmol C m-3 d-1). In addition, BP increased in the bottom water incubation amended with SDOM-containing pore water (PW). The results demonstrated that SDOM contains bio-reactive forms of DOM that stimulate heterotrophic microbial metabolism at the expense of oxygen in the bottom water layer. The accumulation of C1 component in both PW-amended and unamended bottom water incubation (i.e., without an extra DOM supply from sediment) further indicated that refractory DOM is produced autochthonously in the water column via heterotrophic metabolic activity. This explains in part the microbially mediated accumulation of excess FDOMH in the deep-water column of the UB. Overall results suggest that the benthic release of bio-reactive DOM may be of widespread significance in controlling microbial processes in the deep-water layer of marginal seas.

The ecological functions and biogeochemical processes of continental marginal seas are important for the global carbon cycle. In the eastern China marginal seas (ECMS), phytoplankton productivity has increased significantly in recent decades, but the sources and burial processes of marine organic carbon (OC) remain under-studied. We analyzed the contents of marine lipid biomarkers (brassicasterol, dinosterol, and C37 alkenones) in surface suspended particles obtained from seven cruises between 2010 and 2015, and in surface sediments from eight cruises between 2006 and 2012 in the ECMS, to estimate marine OC sources and burial. The correlations between lipid biomarkers and environmental factors were quantified to reveal controlling factors. The study area was divided into four regions according to cluster analysis conducted based on sediment parameters. Our results showed that the concentrations of marine lipid biomarkers in surface water were high near large estuaries such as the Changjiang River Estuary and the Yellow River Estuary, but those in surface sediments were high in mud areas. Nutrient concentration was a key factor controlling phytoplankton biomass in surface water, with high nutrients enhancing the growth of diatoms and dinoflagellates, while haptophytes were more abundant in low-nutrient, high-salinity and cold environments. High marine OC contents calculated from total OC δ13C were mainly associated with fine sediments transported by coastal currents, and finally deposited in mud areas. The proto-burial efficiency of marine OC in the ECMS (7–19%) was markedly higher than the mean value in global marginal seas, with high values being located in the western coast of the ECMS. The proto-burial efficiency of total marine lipid biomarkers (6–24%) was quantified for the first time in our study, with overall values and spatial patterns similar to that of marine OC. A key parameter for marine OC and marine biomarker proto-burial efficiency was sediment grain size. The smaller the sediment grain size was, the better the marine OC and marine biomarker were retained. Our study provides an important basis to elucidate spatial distribution patterns and forcing mechanisms of marine OC in surface water (production process) and surface sediments (burial process), and to estimate carbon budgets in large marginal seas.

Particulate organic carbon (POC) is one of the essential variables in oceanic biogeochemical processes. Assessing the spatiotemporal variability of POC will help deepen our understanding of the carbon cycle. In this study we collected moderate-resolution imaging spectroradiometer (MODIS) Aqua satellite data for surface POC in Indonesian waters during the period 2002–21, together with in situ data from the south-western Sumatran waters (SSW), Sunda Strait, Sumba–Savu waters and the Halmahera Sea and surrounds. These data were analysed to gain an understanding of the spatial and temporal variations in POC. Generally, high POC concentrations in Indonesian waters were found at coastal and continental shelves connected to the estuaries of large rivers; we assume that the POC concentrations in these areas are affected by terrestrial input. Meanwhile, in Indonesian waters apart from these estuaries, marine-derived materials are the main components of POC. The seasonal pattern of POC in Indonesian waters generally shows highest levels during the south-east monsoon and lowest levels during the north-west monsoon. Trends in POC concentrations are positively correlated with chlorophyll- a and negatively correlated with sea surface temperature. This study suggests that the combination of natural physicochemical processes and anthropogenic perturbations has significant effects on spatial and temporal variations in POC in Indonesian waters. High particulate organic carbon (POC) concentrations were found mainly at the coastal and continental shelves connected to estuaries. The seasonal pattern of POC shows highest levels during the south-east monsoon and lowest levels during the north-west monsoon. The combination of natural physicochemical processes and anthropogenic perturbations has significant effects on spatial and temporal variations in POC. The MODIS product of POC underestimates the actual POC in the region of the Halmahera Sea and surrounds; thus, a regional algorithm is necessary for future studies. [ABSTRACT FROM AUTHOR]

Tropical cyclone (TC) intensification over marginal seas, especially rapid intensification (RI), often poses great threat to lives and properties in coastal regions and is subject to large forecast errors. It is thus important to understand the characteristics of TC intensification and the involved key factors affecting TC intensification over marginal seas. In this study, the 6-hourly TC best-track data from Shanghai Typhoon Institute of China Meteorological Administration, ERA-Interim reanalysis data, and TRMM satellite rainfall products are used to analyze and compare the climatological characteristics and key factors of different intensification stratifications over the marginal seas of China (MSC) and the western North Pacific (WNP) during 1980–2018. The statistical results show that TC intensification over the MSC is more likely to occur when TCs experience relatively large intensities, weak vertical wind shear, small translation perpendicular to the coastline, relatively high fullness, strong upper-level divergence, low-level relative vorticity, and high inner-core precipitation rate. The box difference index method is used to quantify the relative contributions of these factors to TC RI. Results show that the initial (relative) intensity contributes the most to TC RI over both the MSC and the WNP. The inner-core precipitation rate and translation perpendicular to the coastline are of second importance to TC RI over the MSC, while both vertical wind shear and TC fullness are crucial to TC RI over the WNP. These findings may help understand TC activity over the MSC and provide a basis for improving intensity prediction of TCs in the MSC.

Burial of terrestrial organic carbon (OC terr) in marginal sea sediments is a key component of the carbon cycle, exerting long-term influence on atmospheric CO 2 and climate. Assessment of the burial efficiency of OC terr is of key importance, yet remains poorly constrained due to current gaps in our knowledge of mechanistic controls, including the influence of organic matter composition and age on the fate of OC terr in marine sediments. We measured bulk characteristics (δ13C and Δ14C of OC; mineral surface area, SA; grain size; n = 98 samples) and biomarker carbon isotopic compositions (fatty acid δ13C and Δ14C; n = 11) of a suite of surface sediment samples from the Bohai Sea and Yellow Sea (BS-YS). Combining with published results, bulk OC (n = 234) and biomarker (n = 19) carbon isotopic data are used to examine spatial variability in the sources and ages of OC terr in this shallow marginal sea system. Biomarker carbon isotopic values are used to constrain endmember values, and a dual carbon isotope mixing model was applied to all bulk samples to develop a spatially explicit assessment of contributions of different pools of OC terr. Although highly spatially variable, pre-aged OC (OC pre-aged) and fossil OC (OC fossil) when combined (i.e., "non-modern OC") on average accounted for 51 ± 10% of the OC in BS-YS surface sediments. This was equivalent to the proportion of OC terr (ave., 51 ± 14%) estimated from a δ13C OC binary mixing model, suggesting OC terr in the mixed layer of BS-YS sediments is predominantly composed of millennial-aged OC. The burial potential of pool-specific OC terr was then evaluated through comparison of corresponding mineral SA-normalized loadings of surface sediments with those of Yellow River suspended particulate matter. Both the regression slope and the arithmetic mean value approaches reveal high burial potential for all terrestrial OC pools delivered by Yellow River, which is attributed to the aged and refractory nature of OC exported from the Yellow River. However, differing relationships of pool-specific OC terr loadings between BS-YS and Yellow River sediments imply contrasting fates. In particular, we find that the burial potential of OC pre-aged is consistently greater than that of OC fossil. This surprising observation suggests either enhanced degradation of OC fossil during lateral transport (possibly as a consequence of different mineral associations and hydrodynamic sorting effects), or additional sources for OC pre-aged , such as from small rivers or aerosol deposition. Overall, OC age, mineralogical composition and hydrological settings contribute to the complex patterns of OC residing in northern China marginal sea surface sediments. This novel molecular-isotopic approach reveals significant spatial variability in proportions, contents and burial potential among terrestrial OC pools, and underlines the importance of considering organic matter age and composition in understanding and constraining the fate of OC terr in marine sedimentary environments. [ABSTRACT FROM AUTHOR]

One of the most important breakthroughs in oceanography in the last 30 years was the discovery that iron (Fe) controls biological production as a micronutrient, and our understanding of Fe and nutrient biogeochemical dynamics in the ocean has significantly advanced. In this review, we looked back both previous and updated knowledge of the natural Fe supply processes and nutrient dynamics in the subarctic Pacific and its impact on biological production. Although atmospheric dust has been considered to be the most important source of Fe affecting biological production in the subarctic Pacific, other oceanic sources of Fe have been discovered. We propose a coherent explanation for the biological response in subarctic Pacific high nutrient low chlorophyll (HNLC) waters that incorporates knowledge of both the atmospheric Fe supplies and the oceanic Fe supplies. Finally, we extract future directions for Fe oceanographic research in the subarctic Pacific and summarize the uncertain issues identified thus far. [ABSTRACT FROM AUTHOR]

The coupling relationship between biogenic deposits and productivity may vary across different stages or regions. To explore the responses of biogenic deposits to productivity since the last glacial period, we analyzed multiproxy biogenic deposit data from Core YDY09 in the Bay of Bengal (BoB) spanning the past 30 ka. We first observed that the trends of biogenic depositional records (radiolarians, BSi, and CaCO 3) were in antiphase to that of the productivity of siliceous organisms in the overlying waters during the Last Glacial Maximum (LGM), Heinrich Stadial 1 (HS1) and late deglacial period (LdGp; 15–10 ka) in the northeastern Indian Ocean. We suggest that productivity variations were influenced mainly by the Indian summer monsoon (ISM) during the last deglaciation to glaciation. The decoupling between high productivity and low biogenic deposition during the LGM and LdGp was attributable to significant dilution by large-scale terrigenous inputs. Unlike the substantial inputs of terrestrial materials caused by low sea levels during the LGM period, the sea level rose rapidly during the LdGp period, suggesting that the intense ISM may have played a crucial role at that time. Conversely, the high amount of biogenic deposition during HS1 could be attributed to weak terrigenous dilution resulting from diminished rainfall in the Intertropical Convergence Zone (ITCZ). The strong terrigenous dilution observed during the LGM and weak terrigenous dilution during the HS1 in the BoB were consistent with findings in the northern South China Sea (SCS), except the unique LdGp period. Our findings will enhance the understanding of the decoupling mechanisms between biogenic deposits and productivity in global marginal seas. • Biogenic deposit records (Radiolaria, BSi) since the 30 ka from Bay of Bengal. • Indian summer monsoon modulates productivity pattern. • Biogenic deposition and productivity decouple during last deglaciation-glaciation. • Different mechanisms of terrigenous inputs during LGM and late deglaciation. • Reduced ITCZ rainfall weakened terrigenous inputs during Heinrich Stadial 1. [ABSTRACT FROM AUTHOR]

This article describes oxygen distributions and recent deoxygenation trends in three marginal seas – Persian Gulf and Red Sea in the Northwestern Indian Ocean (NWIO) and Andaman Sea in the Northeastern Indian Ocean (NEIO). Vertically mixed water column in the shallow Persian Gulf is generally well-oxygenated, especially in winter. Biogeochemistry and ecosystems of Persian Gulf are being subjected to enormous anthropogenic stresses including large loading of nutrients and organic matter, enhancing oxygen demand and causing hypoxia (oxygen < 1.4 ml l–1) in central and southern Gulf in summer. The larger and deeper Red Sea is relatively less affected by human activities. Despite its deep water having remarkably uniform thermohaline characteristics, the central and southern Red Sea has a well-developed perennial oxygen minimum at mid-depths. The available data point to ongoing deoxygenation in the northern Red Sea. Model simulations show that an amplified warming in the marginal seas of the NWIO may cause an intensification of the Arabian Sea oxygen minimum zone (OMZ). Increases in particulate organic carbon and decreases in oxygen contents of the outflows may also have a similar effect. In the Andaman Sea, waters above the sill depth (∼1.4 km) have characteristics similar to those in the Bay of Bengal, including an intense OMZ. As in the case of the Bay of Bengal, oxygen concentrations within the Andaman Sea OMZ appear to have declined slightly but significantly between early 1960s and 1995. The exceedingly isothermal and isohaline water that fills the deep Andaman Basin is also remarkably homogenous in terms of its oxygen content. A very slight but statistically significant decrease in oxygen content of this water also seems to have occurred over three decades preceding 1995. New information is badly needed to assess the extent of further change that may have occurred over the past 25 years. There have been some reports of coastal “dead zones” having developed in the Indian Ocean marginal seas, but they are probably under-reported and the effects of hypoxia on the rich and diverse tropical ecosystems – coral reefs, seagrasses, and mangroves – in these seas remain to be investigated.

Continental shelf sediments are an important source of iron (Fe) in the oceans. Observational data suggest that basin‐scale transport of sedimentary sourced Fe accompanies the ventilation of the intermediate layer in the North Pacific. Here we use a marine biogeochemical model to explore the Fe transport mechanism with a focus on the role of sinking particles. The lateral penetration of sedimentary sourced Fe was best simulated when we assumed a short desorption and disaggregation length scale of Fe from sinking particles. The simulation results indicated that Fe is laterally transported mainly through interactions with particles with sinking velocities of 180–460 m yr−1; these velocities are two orders of magnitude slower than typical sinking rates of marine aggregates determined from mass flux measurements. Slowly sinking particles drive the basin‐scale transport of Fe by prolonging its residence time and by injecting sedimentary sourced Fe supplied originally to less dense waters into the intermediate layer water across isopycnal surfaces. A large amount of Fe from shelf sediments of the Okhotsk and Bering Seas is exported to the North Pacific through this particle interaction. These results highlight a biogeochemical linkage between the marginal seas and ocean basins that has been overlooked in global ocean models. Plain Language Summary: Iron (Fe) is an essential micronutrient for marine phytoplankton, and understanding its source and cycle in the ocean is essential for understanding the future carbon cycle and thus climate change. Although continental shelf sediments have been thought to be a major Fe source, how Fe, which is hardly soluble in seawater, is transported to the open ocean is still unclear. We used a numerical model simulating marine biogeochemical cycles to investigate the transport mechanism and found that Fe is transported long distances in association with slowly sinking particles. Our results suggest that a large amount of the Fe in North Pacific waters comes from marginal sea shelf sediments. Key Points: Slowly sinking particles extend the residence time of iron in the ocean and support the long‐range transportAdsorption and aggregation, and desorption and disaggregation processes likely control generation of iron‐rich and slowly sinking particlesSubstantial amounts of iron supplied from continental shelf sediments in the marginal seas are exported to the North Pacific [ABSTRACT FROM AUTHOR]

Near‐inertial internal waves (NIWs) in the abyssal Yamato and Tsushima Basins of the Japan Sea (East Sea) were investigated using data from a moored acoustic Doppler current profiler (ADCP) and single‐point current meters. The NIW events with duration of 3–5 days were observed intermittently in both basins. In particular, an active NIW event occurred below 2,475 m in the Yamato Basin during May 12–16, 2014. This was followed by the upward propagation of a wave packet from 2,475 to 950 m. The near‐inertial flows (1.07f) during the event exhibited a vertically coherent phase and intensification with depth by a factor of 1.5 from 2,475 to 2,635 m. The near‐inertial flows (1.05f) in the Tsushima Basin also showed a vertically coherent phase and intensification with depth, although the amplitude of the flow exhibited a middepth maximum rather than monotonic intensification. As a possible explanation of the observed flow characteristics, the superposition of downward‐propagating NIWs that can be excited by a strong wind event and upward‐propagating NIWs that bounced off the seabed was examined. The time series of the Richardson number based on the observed shear showed sporadic unstable conditions during the initial stage of the NIW event during May 2014 in the Yamato Basin. In addition, relatively small values of Richardson number were observed over the range of 2,475–2,635 m during the period of active NIWs. This suggests the promotion of vertical mixing in the deep sea during significant NIW events. Plain Language Summary: The Japan Sea, a semi‐closed marginal sea in East Asia, has its own circulation system driven by the deep water formation. We carried out deep flow observations in the sea 4 times using moored acoustic current meters. The current meters recorded strong flow events accompanying clockwise‐rotating cyclic flows of 18–20 h periods. The cyclic flow, called the near‐inertial flow, is associated with internal waves that are affected by the Earth rotation. The amplitude of near‐inertial flow during the events varied vertically, although the direction of the flow was consistent throughout the observational depths. We tried to explain the observed flow intensification with depth by the superposition of downward‐propagating internal wave that can be excited by a strong wind and upward‐propagating internal wave that bounced off the seabed. In addition, we suggested that the intensification of near‐inertial flow during the events promoted vertical mixing in the deep sea which controls pattern and strength of the deep circulation. Key Points: Near‐inertial flow events with 3–5 days duration were observed in the abyssal Japan Sea using moored current metersNear‐inertial flows during the events exhibited a vertically coherent phase and varying amplitude with depthSuperposition of near‐inertial internal waves was suggested as a cause of the deep flow intensification that promotes vertical mixing [ABSTRACT FROM AUTHOR]

The microbial cycling of dimethylsulfoniopropionate (DMSP) and its gaseous catabolites dimethylsulfide (DMS) and methanethiol (MeSH) are important processes in the global sulfur cycle, marine microbial food webs, signaling pathways, atmospheric chemistry, and potentially climate regulation. Many functional genes have been identified and used to study the genetic potential of microbes to produce and catabolize these organosulfur compounds in different marine environments. Here, we sampled seawater, marine sediment and hydrothermal sediment, and polymetallic sulfide in the eastern Chinese marginal seas and analyzed their microbial communities for the genetic potential to cycle DMSP, DMS, and MeSH using metagenomics. DMSP was abundant in all sediment samples, but was fivefold less prominent in those from hydrothermal samples. Indeed, Yellow Sea (YS) sediment samples had DMSP concentrations two orders of magnitude higher than in surface water samples. Bacterial genetic potential to synthesize DMSP (mainly in Rhodobacteraceae bacteria) was far higher than for phytoplankton in all samples, but particularly in the sediment where no algal DMSP synthesis genes were detected. Thus, we propose bacteria as important DMSP producers in these marine sediments. DMSP catabolic pathways mediated by the DMSP lyase DddP (prominent in Pseudomonas and Mesorhizobium bacteria) and DMSP demethylase DmdA enzymes (prominent in Rhodobacteraceae bacteria) and MddA-mediated MeSH S-methylation were very abundant in Bohai Sea and Yellow Sea sediments (BYSS) samples. In contrast, the genetic potential for DMSP degradation was very low in the hydrothermal sediment samples—dddP was the only catabolic gene detected and in only one sample. However, the potential for DMS production from MeSH (mddA) and DMS oxidation (dmoA and ddhA) was relatively abundant. This metagenomics study does not provide conclusive evidence for DMSP cycling; however, it does highlight the potential importance of bacteria in the synthesis and catabolism of DMSP and related compounds in diverse sediment environments.

The fate of terrestrial organic carbon (OCterr) exported from large rivers in marginal seas is an integral component of land‐ocean‐atmosphere carbon dynamics and influences on atmospheric CO2 concentrations on millennial and longer timescales. In this study, we employ a novel approach to constrain burial efficiencies for source‐specific terrestrial biomolecules (long‐chain n‐alkanes and n‐fatty acids) in two river‐marginal sea systems. We find for the Pearl River‐South China Sea system that 34 ± 19% and 11 ± 4% of n‐alkanes and n‐fatty acids, respectively, are preserved across the transport pathway from the river mouth to inner shelf. In contrast, terrestrial biomolecular burial efficiencies were markedly higher (64 ± 17% and 84 ± 30% of n‐alkanes and n‐fatty acids, respectively) in the Yellow River‐Bohai Sea/Yellow Sea system. These findings reveal markedly different fates of OCterr in these two fluvial‐marine systems, as well as sharp contrasts in OCterr reactivity within each system. Plain Language Summary: Burial efficiencies of source‐specific biomarker compounds in coastal sediments can provide new insights into the fate of terrestrial organic carbon in marine environments. In this study, we determine mineral surface area‐normalized loadings of higher plant‐derived long‐chain n‐alkanes and n‐fatty acids in two Chinese fluvial/marginal sea systems in order to examine terrestrial organic carbon burial efficiencies. We find marked contrasts in terrestrial organic carbon burial efficiency between both fluvial systems and terrestrial biomolecules. These differences imply sharply contrasting fates of different components of terrestrial organic matter during transport and sedimentation, which in turn shed new light on underlying mechanisms and carry implications for interpretation of past and present‐day variations in terrestrial organic carbon sequestered in continental margin sediments. Key Points: We employ a novel approach to constrain burial efficiencies for source‐specific terrestrial biomolecules in two fluvial/marine systemsTerrestrial biomolecular burial efficiencies decrease along transport pathway, reflecting degradation during dispersal and sedimentationTerrestrial biomolecular burial efficiencies are much higher in Yellow River‐Bohai Sea/Yellow Sea than those in Pearl River‐South China Sea [ABSTRACT FROM AUTHOR]

The microbial cycling of dimethylsulfoniopropionate (DMSP) and its gaseous catabolites dimethylsulfide (DMS) and methanethiol (MeSH) are important processes in the global sulfur cycle, marine microbial food webs, signaling pathways, atmospheric chemistry, and potentially climate regulation. Many functional genes have been identified and used to study the genetic potential of microbes to produce and catabolize these organosulfur compounds in different marine environments. Here, we sampled seawater, marine sediment and hydrothermal sediment, and polymetallic sulfide in the eastern Chinese marginal seas and analyzed their microbial communities for the genetic potential to cycle DMSP, DMS, and MeSH using metagenomics. DMSP was abundant in all sediment samples, but was fivefold less prominent in those from hydrothermal samples. Indeed, Yellow Sea (YS) sediment samples had DMSP concentrations two orders of magnitude higher than in surface water samples. Bacterial genetic potential to synthesize DMSP (mainly in Rhodobacteraceae bacteria) was far higher than for phytoplankton in all samples, but particularly in the sediment where no algal DMSP synthesis genes were detected. Thus, we propose bacteria as important DMSP producers in these marine sediments. DMSP catabolic pathways mediated by the DMSP lyase DddP (prominent in Pseudomonas and Mesorhizobium bacteria) and DMSP demethylase DmdA enzymes (prominent in Rhodobacteraceae bacteria) and MddA-mediated MeSH S-methylation were very abundant in Bohai Sea and Yellow Sea sediments (BYSS) samples. In contrast, the genetic potential for DMSP degradation was very low in the hydrothermal sediment samples— dddP was the only catabolic gene detected and in only one sample. However, the potential for DMS production from MeSH (mddA) and DMS oxidation (dmoA and ddhA) was relatively abundant. This metagenomics study does not provide conclusive evidence for DMSP cycling; however, it does highlight the potential importance of bacteria in the synthesis and catabolism of DMSP and related compounds in diverse sediment environments. [ABSTRACT FROM AUTHOR]