Coastal Currents Research Articles

Prediction of tidal-driven currents using convolutional neural network

Efficient forecasting models of coastal currents are required for the predictive control of smart vessels with autonomous or remote operating capabilities. Accurate physics-based numerical models demand computational resources that often are unavailable onboard ships; moreover, internet bandwidth at remote locations might not be sufficient to exchange the large computational files with onshore servers. In this case, light and efficient Data-Driven Models (DDM) may be developed to be used as a surrogate for a physics-based model.Currents and surface elevation are hydrodynamic variables driven by astronomic tide potential, allowing for harmonic analysis and synthesis of otherwise irregular solutions of Navier-Stokes equations. Once numerical solutions are obtained and analysed in the Fourier domain, the identified harmonics (tide constituents) can be used as a dataset to train the DDM. One approach to building a DDM is by utilizing a Convolutional Neural Network (CNN).CNN is mainly applied in image recognition processes, where it learns the spatial features of image matrices of pixels arranged in columns and rows and uses the learned features to predict an output. This approach can be applied to 2D or 3D fields of predominantly tidal-driven coastal currents. This paper extends the CNN framework to approximate and predict coastal hydrodynamic state variables in space and time. The depth-averaged Navier-Stokes equations were used to create the dataset necessary to train the adopted CNN autoencoder architecture.Two methods of CNN model development are explored. The first method assesses CNN’s capabilities for time forward prediction, using 2D time series of hydrodynamic variables. The second method investigates CNN’s parameter (using Manning number) prediction ability using 2D spatial plots formed by the top 20 most energetic tidal constituents that were obtained from the numerical solution. The hyperparameters of the CNN model for both methods were carefully optimized and tuned using the loss function, Root Mean Square Error (RMSE). The coefficient of determination, the relative error of the time series, and its amplitude and phase were used to gauge the performance of the CNN model for both methods at the final testing stage.Once accurate solutions are achieved, the trained DDM is almost instantaneous and uses negligible computational resources as compared to traditional fluid solvers. Therefore, trained DDM can be deployed onboard ships where global forecast information (e.g., from Global Forecast System) can be used to provide an accurate prediction of the current forcing. To generate the instantaneous current predictions for navigation and smart ship control, the global data can be pulled or pushed to the ship before the mission.

Термохалинные характеристики и пространственное распределение хлорофилла на стандартном разрезе “Кольский меридиан” в апреле 2021 года

In the Barents Sea, the major part of the annual primary pelagic production is formed during the spring phytoplankton bloom. A phytoplankton bloom is understood as an annually recurring increase in its total biomass. Chlorophyll a concentration reflects changes in phytoplankton biomass and can serve as an indicator of production characteristics. In April 2021, the thermohaline characteristics of the water column and the distribution of chlorophyll a concentrations along a standard transect “Kola Section” were studied. The Transect was located in the path of the warm waters of the Nordkapp current and the desalinated waters of the Murmansk coastal current. Coastal, Atlantic and Arctic waters were defined along the Transect. Chlorophyll a concentrations in coastal waters varied on average from 0.57 to 0.86 mg/m3 (maximum 1.11 mg/m3), in Atlantic waters from 0.11 to 0.34 mg/m3 (maximum 0.50 mg/m3). At the station located in the area of intensive interaction of two types of waters (in the area of salinity and temperature fronts) maximum concentrations of chlorophyll a (0.96–1.39 mg/m3) were noted. The location and extent of zones of increased (or decreased) chlorophyll a concentrations agreed with the alternation of water masses. The beginning of the early spring phytoplankton bloom was in the coastal zone of Central Murman.

A 140-year record of environmental changes in São Sebastião, Brazil

Over the past two centuries, coastal and estuarine areas have experienced environmental stress due to rapid population growth, leading to higher demand, overexploitation, habitat transformation, and pollution, which have severe consequences on the overall ecosystem and human health. This work aims to understand historical perspectives of such environmental stress in a coastal area of São Sebastião city in the São Paulo State of Brazil, which has witnessed rapid changes in land use over the past 60–70 years. We collected eleven surface sediments and one 64 cm long core from the shallow water depth sector of the São Sebastião Channel (SSC), adjacent to the Araçá Bay region. Sediments were dominantly composed of terrestrial siliciclastic material carrying signatures of both local inputs (i.e., weathered granitic and gneissic rocks of Serra do Mar Mountain ranges) and Plata Plume sediments brought by Brazilian coastal currents. Low sediment accumulation (avg. = 0.10 cm yr−1) between 1880 and 1947 showed a stable environment followed by an abrupt increase in sedimentation (avg. = 0.84 cm yr−1) from 1947 to 2017. This approximate eight-fold increase in sedimentation after 1947 marked significant anthropogenic changes in the region, which is coincidental with major changes in land use through the construction of the port of São Sebastião (1930s) and BR-101 Highway (1980s). While recent surface sediments showed no pollution of heavy metals, anthropogenic Zn enrichment was found between 1880 and 2000. Zn enrichment was from the combined sources, e.g., agriculture activities, domestic sewage, and possibly Zn coated ship paints. Our study also indicates that planned future expansion of São Sebastião port may further increase the sedimentation rate in SSC and impact the ecosystem of Araçá Bay and SSC.

Scale-dependent assumptions influence habitat suitability estimates for the American lobster (Homarus americanus): Implications for a changing Gulf of Maine

Bioclimate envelope models were evaluated for possible spatial nonstationarity for American lobster (Homarus americanus) in the Gulf of Maine (GOM). Five environmental variables were considered, including bottom water temperature, bottom water salinity, distance offshore, sediment grain size, and latitude. Three models accounting for varying degrees of spatial nonstationarity were developed and evaluated. Spatial scales developed in these models were determined by the patterns of the GOM coastal currents and the associated affects these currents have on the GOM oceanography. This study suggests that incorporating spatial nonstationarity into habitat suitability modeling may lead to improved models. Forecast plots for the 2028−2055 period revealed that traditional modeling techniques applied at coarse spatial scales estimated higher suitability of habitat for juvenile lobsters than models at smaller spatial scales. For adult lobsters, coarse spatial model yielded higher suitability in both coastal waters in western GOM and farther offshore waters in eastern GOM, and generally estimated lower suitability in coastal eastern GOM waters and some offshore western GOM waters, compared to finer-scale spatial models. These results demonstrate how HSI estimates would vary based on the choice of spatial scales and its consequences. This information could benefit future stakeholders to prepare and adapt at more localized scales for changes that may occur in a region that is susceptible to climate change.

Going With the Flow – Population Genetics of the Kelp Saccharina latissima (Phaeophyceae, Laminariales)

Saccharina latissimais the most important habitat-forming kelp in sheltered areas of North-Atlantic, and there is also an increasing interest in cultivation and utilization ofS. latissima. The cultivation activity may introduce a risk of “crop-to-wild” gene flow from the cultivated crops to natural populations. A baseline study to examine genetic structure and gene flow inS. latissimaalong the Norwegian coast was therefore done. Microsatellite analyses was carried out on samples from 21 stations, where 12 were in the coastal area from outer Oslofjord in the south to Porsanger in North-Norway, and 9 in the two longest fjords of Norway, Hardangerfjord and Sognefjord. In addition, a hydrographical model was applied, simulating the direction and potential rate of spore dispersal along the coast during the main period of spore release. The results showed a clear isolation by distance pattern along the coast, good connectivity and little genetic structure, except for a reduced connectivity between South- and North-Norway, probably due to the Lofoten archipelago representing a partial barrier for the northward dispersal of spores. In addition, indications of reduced connectivity between coastal stations and the innermost fjord stations were found. Analysing the material with and without one locus potentially under positive selection suggests some degree of genetic adaptation of sugar kelp populations in the Skagerrak area and in the two fjords. The results suggest that genetic connectivity between populations on the coast is strongly influenced by the Norwegian Coastal current.

The sub-fossil diatom distribution in the Beibu Gulf (northwest South China Sea) and related environmental interpretation.

Located in northwestern South China Sea (SCS), the Beibu Gulf constitutes an environmentally sensitive region shaped by land-ocean-atmosphere interactions in Asia between the western Pacific and eastern Indian Oceans. This study aims to provide a comprehensive view of the sub-fossil diatom biogeography, distribution pattern and oceanographic environmental controls with support of multivariate methods based on Beibu Gulf core-top samples. Cluster analysis of diatom assemblages divides the distribution pattern into four subclusters. Sea surface salinity (SSS), temperature (SST), trophic state (chlorophyll a concentration in this study) and water depth constrain the diatom distribution pattern through canonical redundancy analysis although only partly support an interpretation of the relationship between these various variables. Chlorophyll a has a strong correlation to diatom distribution, and responds to Paralia sulcata occurrence, while SSS and SST also have significant influence and indicate warm water invasion from the open SCS. Water depth is a subordinate factor in terms of Beibu Gulf diatom distribution. The ca. 25 m water-depth marks the upper extent of Paralia sulcata dominance in the northern Beibu Gulf. A strong mixing area with a complex diatom distribution exists below this water depth in the middle of Beibu Gulf. Coastal currents from north of SCS invade Beibu Gulf through Qiongzhou Strait and south of Hainan Island, as recorded by higher percentages of Paralia sulcata and Cyclotella striata at these sites. Our results provide a selection of evaluation method for a marine ecological red-line definition for sustainable development. This study highlights the perspective relationships between the spatial distribution of sub-fossil diatom assemblages in surface sediments and oceanographic variables, which could serve as a model for paleoenvironmental and paleoclimatic reconstruction in future marginal sea geoscience research for the Beibu Gulf, northwestern SCS.

Nitrogen fixation in the western coastal Bay of Bengal: Controlling factors and contribution to primary production

N2 fixation rates were measured at 18 stations in the western coastal Bay of Bengal (BoB) to evaluate its contribution to the external source of nitrogen and its controlling factors. During the study period (fall monsoon), East India Coastal Currents (EICC) flows equatorward resulting in spreads of low saline water along the coast. This leads to stratification and inhibition of nutrient supply to the mixed layer through vertical mixing, resulting in the existence of nitrogen-poor and warm waters in the upper layer. Such conditions may trigger N2 fixation in the upper ocean. To examine such possibility, the N2 fixation rates were measured and found to vary between 0.4 and 14.8μmol N m−2 d−1 in the photic layer during the fall monsoon. A linear relationship was observed between photic zone integrated N2 fixation rates and phosphate suggesting a possible severe limitation of phosphate in the BoB. Low N2 fixation rates were observed at off Godavari, Krishna and Mahanadi River estuaries in the inshore than offshore regions associated with low phosphate and high suspended matter. This suggests that phosphate may be removed through adsorption on the suspended matter resulting in severe limitation of N2 fixation in the western BoB. Based on the available seasonal data, 0.01 to 0.94 Tg/y of N2 fixation occurs and contributes to <1% of the primary production in the BoB.

An Integral View of the Gulf of Tonkin Seasonal Dynamics

AbstractAs part of a U.S. – Vietnam collaborative effort, a numerical model is used to describe the dynamics associated with the Gulf of Tonkin seasonal variability. Unique to this study is the synthesis of historical and recent observations throughout the gulf that are leveraged to validate the model's seasonal component. The dynamics is primarily forced by seasonally reversing monsoons, remote transports through the Qiongzhou Strait and by the western boundary current, and river discharge. Monsoonal winds set up pressure gradients across the gulf that tend to be balanced by geostrophic flows (cyclonic during the winter and anticyclonic during the summer). However, a number of processes modify the wind‐driven dynamics with all of them promoting cyclonic circulation. In the eastern region, the tides influence the seasonal variability via (a) a tidal‐residual flow producing an influx of mass through the Qiongzhou Strait and (b) through modification of the summer baroclinic density field. In the western region, the seasonal variability can be strongly dependent on river buoyancy flows and intrusions of the western boundary current. Southwest summer winds produce a low salinity bulge near the Red River mouth that releases and advects as a southward coastal current during the fall as winds relax and reverse direction. Additionally, the vorticity budget shows that topographic steering constrains the seasonal variability promoting intrusions of the western boundary current during winter monsoon conditions, when the current carries water of shallow origin from the Chinese shelf.

Conditions of sand spits formation at the Northern Sea of Azov coast

Term “spits of the Azov type” is encountered in the description of morphological features of sandy accumulative forms of sea coasts. This term is related to a system of several parallel spits in the form of narrow strips extended into the open sea over a few kilometers and formed under the influence of wind waves with acute incidence angles to the coastline. Term “spits of the Azov type” was introduced into everyday life by V.P. Zenkovich, who actively studied the shores of the Black Sea-Azov basin, as applied to the spit system of the northern coast of the Sea of Azov. It is shown in our work, based on a detailed analysis of the hydrodynamic regime of the Sea of Azov over the past four decades that wind waves with acute angles do not determine the features of the wave climate of the northern coast. The main factor in the development of spits from the open sea is wind waves that are normal to the coast, while the factor on the mainland side are coastal currents that are formed over the background of storm surges. Thus, the application of term “spits of the Azov type” to sea spits of the other coasts of the World Ocean formed by wind waves with acute angles of wave approach does not seem justified.

Micro- and macro-habitat selection of Atlantic salmon,Salmo salar, post-smolts in relation to marine environmental cues

AbstractAtlantic salmon is an economically and culturally important species. The species encounters several natural and man-made threats during its migration between fresh water and the ocean, which in combination may explain its ongoing decline. With the aim to better understand whether post-smolt behaviour is influenced by physical oceanographic conditions, the migratory behaviour of 173 post-smolts in a high-latitude Norwegian fjord was investigated, combining acoustic telemetry with site- and time-specific environmental variables from an oceanographic model. Most post-smolts (94%) performed a unidirectional migration out the fjord. Progression rates were relatively high (0.42–2.41 km h−1; 0.84–3.78 BL s−1) and increased with distance from the river. While post-smolts had an affinity for lower salinities in the inner fjord, statistical models failed to detect any significant relationship between the small-scale (within arrays) migratory behaviour and salinity, temperature, or coastal surface currents within the fjord. In the outer part, the post-smolts predominantly exited the fjord system through the strait with the highest surface salinities and lowest temperatures, independently of the current direction. Our findings indicate that the macro-habitat selection of the Atlantic salmon post-smolts was influenced by environmental factors: the post-smolts directed their migration towards “ocean cues.” However, this was not confirmed on the micro-habitat level.

On Investigating the Dynamical Factors Modulating Surface Chlorophyll-a Variability along the South Java Coast

Twelve years of remotely sensed all-sat merged chlorophyll-a concentration unveils strong signatures of chlorophyll-a blooms along the south Java coast. An unprecedented three-times increase in chlorophyll-a concentration is significantly observed along the south Java coast during the southeast monsoon (June–October) than the northwest monsoon (December–April). The multiple regression analysis of dynamic factors evidently indicates that seasonal upwelling is predominantly controlled by the seasonally evolving coastal eddies associated with the seasonally reversing south Java coastal currents (SJCC) and Ekman mass transport (EMT), followed by the relative roles of sea surface temperature (SST) and wind stress curl. The eddy-induced upwelling and EMT-induced coastal upwelling lead to chlorophyll-a blooms during southeast monsoon, well-supported by the entrainment of cold and saline waters (thermocline doming) with low spiciness. On the other hand, the coastal eddies associated with SJCC and SST anomalies play a significant role in modulating the interannual surface chlorophyll-a variability in the domain. Intense chlorophyll-a blooms are observed during the positive IOD years, whereas the least chlorophyll-a concentration is observed during the negative IOD years. The unprecedentedly least chlorophyll-a concentrations during 2010 and 2016 are attributed to the intense and prolonged surface marine heatwaves.

Mechanisms of Estuarine Salt‐Plug Formation by an Along‐Shelf Buoyant Current: A Numerical Model Approach

AbstractWhile estuarine salt plugs can develop worldwide in basins adjacent to buoyant coastal currents, their formation has been scarcely documented. This study aims to investigate a mechanism for salt‐plug formation that disregards evaporation processes but involves a buoyant coastal current modified by wind stresses. A numerical model, Delft3D, is used to study the salt‐plug formation in an idealized bay connected to the ocean by a single inlet. Inspired by recent observations, the numerical experiments simulate eight different scenarios of tidal and wind forcing under the influence of an along‐shelf buoyant current. Results show salt‐plug formation that induces inverse exchange at the inlet, with inflow at the surface and outflow underneath. This exchange circulation is modified by wind action. The persistence of the salt plug depends on tidal flushing and on wind forcing. Two numerical experiments with nonstationary buoyant currents and nonstationary winds indicate that: (a) a salt plug forms when a buoyant current is active on the shelf and traps salty water that enters the bay during times of buoyant current relaxation; (b) the presence of the buoyant current induces an inverse circulation at the inlet, modified by the wind action; and (c) onshore and then downwelling winds enhance the inverse circulation at the inlet, while offshore and then upwelling winds stall it. Bay flushing times increase due to the presence of the salt plug. This study represents an initial attempt to identify the role of wind and buoyant coastal currents on salt‐plug formation.

Linkage Between Mangrove Seedling Colonization, Sediment Traits, and Nitrogen Input

Mangroves around the world settle along coasts and estuaries, where they usually encounter aquaculture effluent that causes eutrophication and regulates the nitrogen cycle in their ecosystems. Moreover, the physical–chemical features of sediment in mangrove habitats might be altered by coastal wind, waves, and currents more frequently under the condition of increasing extreme climatic events. These events affect the process of colonization/regeneration of mangroves. To study how exogenous nitrogen input and sediment texture affect root system establishment of mangrove propagules and the early growth of seedlings, in turn, we set up a mesocosm experiment to explore the morphological and physiological responses of the root system of two mangroves, i.e., Kandelia obovata and Sonneratia apetala. We found that the root morphological features of mangrove seedlings mostly showed significant differences across the sediment texture treatment; K. obovata seedlings were more intensively influenced than S. apetala seedlings. It could be ascribed that the roots of K. obovata seedlings were more sensitive to sediment texture than S. apetala seedlings. Conversely, the treatment of exogenous nitrogen input showed a slighter even non-significant influence on the root features of mangrove seedlings. These results suggest that the seedlings of S. apetala and K. obovata performed similarly. In estuaries and coasts featuring eutrophication and various sediment textures, the conservation and restoration of mangroves should consider these conditions to ensure the sustainable development of mangroves.

Sedimentological signatures of river-shelf processes in a wave-dominated delta front

A wave-dominated delta depositional model is characterized by the combined action of riverine-induced processes and sediment reworking by waves and currents. The combination of these natural-driven processes will lead to the formation of a delta-associated sedimentary record that can potentially register changes in prevailing oceanographic and hydrological conditions, including episodic or extreme events, and also anthropogenic-induced changes to the watershed and sediment load. The main objective of this study is to recognize the sedimentological signatures associated with distinct riverine-inner shelf processes in a wave-dominated delta setting. The study is based on high resolution grain size investigation, applying a grain size x standard deviation analysis. The results allowed to differentiate a typical riverine sediment deposit from the sedimentological signature of episodic or more responsive events related to higher flooding and storm-induced wave/current processes. The delta-associated inner shelf deposits vary according to their distance and orientation from the river mouth and water depth (south-north). This indicates that inner shelf sedimentary records show the spatial influence of riverine plume dispersion/deposition, and marine processes (waves resuspension, coastal currents and tides). These results can be considered for analogue model studies, but also to a first assessment related to medium to long term sedimentation pattern and riverine particulate contaminant dispersion and deposition.

Evolution of Physical and Biological Patterns Along the Tropical and South Atlantic Western Boundary: A Satellite Perspective

AbstractWe investigate the spatial and temporal patterns of satellite‐derived sea surface temperature, salinity and chlorophyll‐a concentration along the eastern South American coast. Two decade‐long time series (2002–2019; except for the salinity) allowed us to investigate changes from seasonal to interannual time scales on an array that stretches from the south (42°S) to the north (10°N) of the continent and from isobaths ranging from −50 to −1000 m away from the coast. The novelty of our approach is to assess comparatively the magnitude, variability, and spectrum of these variables following the same isobaths and using the same methodology. This allowed us to examine the influence of large scale ocean circulation patterns entangled with the local forcing systems such as river discharge and coastal currents, and to quantify to what extent these patterns are spatially and temporally consistent. The seasonal cycle of the temperature explains more variance than that of salinity and chlorophyll on average. Comparatively, salinity has a weak seasonal signal, except near major rivers. Significant long‐term trends were observed in specific regions in the salinity time series. Our study revealed distinct interannual changes at 2‐ and 4‐year period in the whole array with the largest spectral peaks near the La Plata and the Amazon Rivers. Within this period band, thermal signals propagate northward along the whole array. Statistical correlations between satellite‐derived variables and several climate indices suggest remote forcing.

An investigation of the Helmholtz and wave-vortex decompositions on surface currents in a coastal region

Recent efforts to observe sea surface height (SSH) fields at less than kilometer spatial resolution using various satellite missions have spurred interest in understanding how well balanced and unbalanced motions can describe the ocean surface current field at finer scales, particularly in coastal regions characterized by complex flows under multiple driving forces (e.g., tides, winds, and low-frequency signals). In this study, we investigated the Helmholtz physical decomposition and wave-vortex decomposition to delineate the balanced and unbalanced motions of coastal surface currents while considering their reasonable justifications individually. The observed and simulated coastal surface currents do not exhibit an evident decomposition of balanced and unbalanced motions when wave-vortex decomposition is applied. Wave-vortex decomposition may not always be valid in coastal regions in which (1) the isotropy, spatial homogeneity, temporal stationarity, and statistical zero-correlations of the current components may not be guaranteed, and (2) multiple geophysical signals and footprints of driving forces are present. In contrast, the stream function obtained from the Helmholtz physical decomposition can be used as a proxy for balanced motions when the variance of vertical currents is weak, except for near-inertial variance. We believe that the Helmholtz decomposition in the physical domain will provide better insights into the dynamical decomposition than that in the spectral domain and can be applied to the analysis of upper ocean dynamics, including the propagation of unbalanced motions and vertical and horizontal structures of ageostrophic currents. Based on our study, SSH fields that will be observed at a very high spatial resolution in upcoming satellite missions will complement ocean current fields at finer scales, particularly in coastal regions characterized by a complex flow geometry.

Invasive Dreissena Mussel Coastal Transport From an Already Invaded Estuary to a Nearby Archipelago Detected in DNA and Zooplankton Surveys.

Coastal waters of Lake Superior are generally inhospitable to the establishment of invasive Dreissena spp. mussels (both Dreissena polymorpha and Dreissena bugensis). Dreissena have inhabited the Saint Louis River estuary (SLRE; largest commercial port in the Laurentian Great Lakes) for over three decades, but only in the last few years have small colonies been found in the Apostle Islands National Lakeshore (APIS, an archipelago situated 85 km to the east of SLRE) A 2017 survey determined a low abundance Dreissena spatial distribution in APIS, with the largest colonies on the north and west islands which suggested potential veliger transport from the SLRE via longshore currents. Our objective in this study was to determine if Dreissena veligers are transported by currents at low densities along the south shore of Lake Superior from the SLRE to APIS. To do so, we used both eDNA (water and passive substrate samples) and zooplankton collection methods at eight sites evenly spaced between the SLRE and APIS with three sampling times over five weeks. Dreissena veligers were consistently detected along the south shore, although at low abundances (veligers per m3 range = 0-690, median = 8), and for every 1 km increase in distance from the SLRE, both veliger counts and water eDNA copy numbers decreased on average by 5 and 7%, respectively. D. polymorpha (suited to estuary habitats) was detected two times more than D. bugensis (better suited to deep-lake habitats). There was not a trend in the veliger size distribution along the south shore, and temperature and calcium concentrations fluctuated around the threshold for Dreissena veliger and adult development, averaging 11.0°C and 14.8 ppm, respectively. Three zooplankton taxa representative of the estuary community-Daphnia retrocurva, Diaphanosoma birgei, and Mesocyclops copepodites-decreased as the distance from the SLRE increased mirroring Dreissena veliger abundance patterns. Findings represent multiple sources of evidence of a propagule "conveyor belt" for Dreissena along the south shore of Lake Superior. We conclude that veligers are functioning as a propagule, using coastal currents to spread from the point of invasion, thereby traversing coastal habitat previously reported as inhospitable to distant habitats suitable for colonization.

Transformation, Fluxes and Impacts of Dissolved Metals from Shallow Water Hydrothermal Vents on Nearby Ecosystem Offshore of Kueishantao (NE Taiwan)

Hydrothermal vents are one of the important sources of major or trace elements in the ocean. The elemental fluxes, however, may be dynamic due to coastal processes and hydrothermal plumes, especially in shallow-water hydrothermal vents. We collected water samples by using the trace-metal clean technique inside and outside two shallow-water hydrothermal vents (white vent: low temperature, high pH; and yellow vent: high temperature, low pH) off Kueishantao Islet, Taiwan, China via SCUBA divers. We analyzed these samples for their hydro-chemical parameters and dissolved elements (Fe, Mn, Mg, V, Cu, and Mo) thereafter. Our results show that dissolved metals’ concentrations were significantly different between the two vents, with higher Mn and Fe in the White Vent than in the Yellow Vent, likely due to the decreased affinity of the dissolved metals for particles in the white vent. We estimated the plume fluxes of dissolved metals from the hydrothermal mouth by multiplying in situ hydrothermal discharge flowrates with metals’ concentrations inside the vents, which were: 1.09~7.02 × 104 kg Mg, 0.10~1.23 kg Fe, 0.08~28 kg Mn, 33.4~306 g V, 2.89~77.7 g Cu, and 54.3~664 g Mo, annually. The results further indicate that such plumes probably have impacted nearby seawater due to coastal currents and particle desorption during transport. Furthermore, the concentrations of biogenic elements could be further modified in seawater, and potentially impact nearby ecosystems on a larger scale. Our study provides information with which to further understand metal redeployment in submarine shallow nearby ecosystems.

The Sources and Burial of Marine Organic Carbon in the Eastern China 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.

Tuning and Development of an Individual-Based Model of the Herring Spawning Migration

Norwegian spring spawning herring is a migratory pelagic fish stock that seasonally navigates between distant locations in the Norwegian Sea. The spawning migration takes place between late winter and early spring. In this article, we present an individual-based model that simulated the spawning migration, which was tuned and validated against observation data. Individuals were modelled on a continuous grid coupled to a physical oceanographic model. We explore the development of individual model states in relation to local environmental conditions and predict the distribution and abundance of individuals in the Norwegian Sea for selected years (2015–2020). Individuals moved position mainly according to the prevailing coastal current. A tuning procedure was used to minimize the deviations between model and survey estimates at specific time stamps. Furthermore, 4 separate scenarios were simulated to ascertain the sensitivity of the model to initial conditions. Subsequently, one scenario was evaluated and compared with catch data in 5 day periods within the model time frame. Agreement between model and catch data varies throughout the season and between years. Regardless, emergent properties of the migration are identifiable that match observations, particularly migration trajectories that run perpendicular to deep bathymetry and counter the prevailing current. The model developed is efficient to implement and can be extended to generate multiple realizations of the migration path. This model, in combination with various sources of fisheries-dependent data, can be applied to improve real-time estimates of fish distributions.