Outer Shelf Region Research Articles

Depositional Model and Controlling Factors of High-Quality Shales of the Wufeng and Longmaxi Formations in Western Chongqing, Sichuan Basin, China.

The enrichment of organic matter is the foundation for a high-quality shale deposition. It is generally believed that high productivity and persistent anoxic conditions facilitate the preservation and enrichment of organic matter. However, there is a lack of investigation into how the dynamic combination of productivity and anoxia affects organic matter enrichment. Here, the black shales of the Wufeng Formation and Longmaxi Formation in the western Chongqing area were selected, where oceanic anoxia and high productivity evolved as a function of the water depth. The main findings were as follows: (1) the distribution of high-quality shales in the Upper Ordovician Wufeng Formation and the Lower Silurian Longmaxi Formation is closely related to the oxygen minimum zone (OMZ), indicating that the physicochemical conditions within the OMZ zone facilitated the development of high-quality shale; (2) in the late period of the Wufeng Formation, intense ocean upwelling in the middle shelf and outer shelf regions caused high productivity where thick-bedded high-quality shales were deposited; and (3) in the early period of the Longmaxi Formation, ocean upwelling weakened, accompanied by the expansion of the OMZ to shallow water regions, and high-quality shales were widely distributed. Based on the above findings, two depositional models were proposed to account for the formation of high-quality shales, and it is suggested that intense ocean upwelling during the late period of the Wufeng Formation and OMZ expansion during the early period of the Longmaxi Formation played crucial roles in facilitating the formation of high-quality shales. These two models present the spatial and temporal variability of high-quality shale development for the first time and can guide shale gas exploration and development strategies.

Sediment provenance of the East Siberian Arctic Shelf and evidence of Holocene climate-driven fluvial events in the Indigirka River based on detrital mineral analysis

Analysis of sediment provenance in the East Siberian Arctic Shelf is crucial for the understanding of source to sink pathways and their link to climatic and environmental changes. In this paper, we conducted detrital mineral analysis on surface sediments and one sedimentary core (LV77–41-1) from the eastern Laptev Sea and the western shelves of the East Siberian Sea. Based on the results of light and heavy mineral analysis in surface sediments, two distinct zones were identified in the eastern Laptev Sea: an eastern zone is characterized by sources from the Lena River and a northern zone is characterized by sources that transition from riverine dominance to more sea-ice transported sources in an offshore direction. In the western part of the East Siberian Sea, detrital mineral assemblages in the outer Indigirka River mouth region are influenced by polygenic sources comprising sediments mainly derived from the river itself, and some material supplied by the Siberian Coastal Current, and the erosion of coastal permafrost and nearby islands. In the outer shelf and basin region, detrital mineral assemblages contain signatures of apatite, garnet, and hypersthene, indicating various material sources are represented, including the Lena River, Taimyr Peninsula, and Kamchatka Peninsula. Integrating this understanding of the sources and transport pathways of surface sediments, detrital mineral analysis of core LV77–41-1 indicate that coarse-grained Holocene sediments were mainly transported by the Indigirka River, with subordinate sources from coastal permafrost erosion, materials carried by Siberian Coastal Current, and island erosion. Since 7 ka BP, four distinct fluvial events have occurred, with the most prominent fluvial event occurring between 4.6 and 4.3 ka when the depocenter shifted significantly toward the sea. The fluvial events occurred following the onset warm periods and the high frequency of volcanic glass observed in layers marking these fluvial events serves as evidence of the influx of glacial meltwater into the Indigirka River basin during these warmer episodes.

Diversity of complex polysaccharide degrading bacteria from the sediments of interlinked high Arctic fjords, Svalbard

Polysaccharides comprise a major component of marine organic matter and are mostly produced by phytoplankton through primary production. The present study reports the polysaccharide degrading ability of cold-adapted heterotrophs from interlinked high Arctic fjords in the Svalbard archipelago. One hundred and ninety-five polysaccharide degrading bacteria isolated from inner and outer fjord sediments, 148 bacterial isolates showed complex polysaccharide degrading enzyme activity. Pectinase was the most predominant polysaccharide-degrading enzyme, followed by agarase, alginate lyase, chitinase, and laminarinase. Xylanase and carboxy methyl cellulase were showed in a relatively lesser activity. Heterotrophic bacterial isolates from the inner and outer shelf regions showed variation in their complex polysaccharide utilization ability. In Kongsfjorden, pectinase producing bacteria were more prevalent in the outer fjord, while chitinase producing bacteria dominated the inner fjord. In Krossfjorden, chitinase producing bacteria were frequently encountered in the outer fjord, whereas pectinase, laminarinase, and alginate lyase producing bacteria dominated the inner fjord. The results of the study indicated that a significant difference in polysaccharide-degrading bacterial phylotypes between the inner and outer fjords (p<0.05). Major polysaccharide-degrading bacteria belonged to phylum Proteobacteria, followed by Firmicutes, Actinobacteria, and Bacteroidetes. The dominant polysaccharide-degrading genera are Marinobacter, Bacillus, Salinibacterium, Alcaligenes, and Planococcus. The findings reveal the availability of a wide range of polysaccharide substrates in fjord sediments and the significant functional role of the heterotrophic bacterial community in the remineralization process of fjord environments.

From shallow-water carbonate ramp to hemipelagic deep-marine carbonate deposition: Part 3. Lithostratigraphy and Formations of the Middle to Late Anisian Bulog sedimentary successions (Bulog Group) in the Dinarides (Bosnia and Herzegovina, Serbia, Montenegro)

In the Middle Anisian the opening of the Neo?Tethys started and this is characterized by a significant change in deposition in the whole Western Tethys Realm. In the Dinarides the Middle to Late Anisian tectonostratigraphic and basin evolution is mirrored by their sedimentary successions. In the Middle Anisian, the evolution of the shallow?water Ravni Carbonate Ramp ended relatively abrupt in the late Pelsonian: a rapid decrease of carbonate production is accompanied by formation of a horst?and?graben topography. This change is expressed by the change in deposition from shallow?water carbonates to deepwater sedimentary rocks, i.e. the Ravni Carbonate Ramp experienced a drowning. Contemporaneously neptunian dikes were formed in the underlying Ravni Formation, filled with deep?water limestones. In the grabens, near to the newly formed escarpments mass transport deposits accumulated. During the time span late Pelsonian to middle Illyrian a general deepening trend is mirrored in the sedimentological trend and the microfacies characteristics. Fossilla ? gerst?tten (mainly cephalopods) and hardgrounds occur widespread in the deeper?water red nodular limestones formed widespread above the Ravni Carbonate Ramp. Around the middle/late Illyrian boundary a second intense pulse of tectonic motions, related to the onset of volcanic activity, resulted in a crosscut of the older horst?and?graben topo graphy. A second generation of neptunian dikes was formed, the blocks tilted, and again mass transport deposits accumulated near to escarpments. The late Illyrian is characterized by an overall deepening trend expressed also in a change in the microfacies characteristics to radiolarian?rich wacke? to packstones. In cases even radio larites or silicified limestones are characteristic sedimentary rocks in late Illyrian to Ladinian times beside silicified volcano?sedimentary rocks. This paper will define the late Middle?Late Anisian red nodular limestones and related sedimentary rocks with mass transport deposits overlying the Ravni Carbonate Ramp on base of new sedimen tological, stratigraphic and micro facies data following the international rules and standards. The palaeo geographic position together with characteristic litho? and microfacies features cause the lithostratigraphic definition of the different units. Included in the newly introduced Bulog Group are: 1) the emended and formalized Bulog Formation and 2) the newly introduced and defined Komarani Formation. The type?section of the Bulog Formation east of Sarajevo (Han Vidovic, central Bosnia and Herzegovina) is revisited. The Komarani Formation is introduced with the type?section in Komarani village (Zlatar Mt. in SW Serbia). The reference sections for the Bulog Formation in SW Serbia (Klisura quarry on Zlatibor Mt.), Bosnia and Herzegovina (Pridvorica locality at Romanija Mt.) and in Montenegro (Boljevici near Virpazar), are defined. In the reference sections some characteristic lithological and microfacies features are better preserved as in the type?section and included in the emendation and formalization of the Bulog Formation. The Bulog Formation at the type?section and all reference sections are in the Late Triassic overlain by the shallow?water carbonates of the Wetterstein and Dachstein Carbonate Platforms. Age and facies equivalent red nodular limestones deposited in the outer shelf region are part of the Middle to Late Triassic Hallstatt Limestone succession. In the type?region of the Hallstatt Limestones these late Middle to Late Anisian red nodular limestones are named Schreyeralm Limestones. The name Schreyeralm Limestone was introduced earlier as the name Bulog Limestone. It is discussed if also in the Dinarides the name Schreyeralm Limestone should be used for such Anisian red nodular limestones deposited in the outer shelf region, for priority reasons, or if they should be included into the Bulog Formation to avoid confusion, for historical reasons.

Tracing ecological fluctuations during the Middle to Late Jurassic of Jhura, Kutch, India, using foraminifera

The aim of this work is to examine ecological patterns by analyzing the distribution of foraminifera in the Jurassic sediments of the Jhura area, Kutch, India. 87 foraminiferal species were recovered, which were analyzed for paleoecological interpretations. Three techniques were employed: 1) Diversity indices, in which four episodes are identified based on different indices values; 2) Clustering and nMDS ordination approaches identify four assemblages of benthic foraminifera, which differ in biotic and abiotic characteristics; 3) Morphogroup analysis, which divides the studied sequence into four paleoecological units. Four depositional episodes are recognized within the studied interval: Episode I (Bajocian to Bathonian), Spirillina polygyrata assemblage shows the calm environment with a high diversity of foraminiferal species and enough nutrients in the outer shelf zone having normal salinity and high level of dissolved oxygen. Episode II (Lower Callovian), Miliammina cf. M. valdensis assemblage occurred in a stressed condition with low diversity of species in a shallower portion of mid-shelf in a hypo-saline environment and reduced oxygen condition having low to average food influx. Episode III (Middle to Upper Callovian), Lenticulina subalata assemblage indicates that this portion deposited in stress-free environmental conditions having normal salinity and well‑oxygenated waters in the deepest section of the outer shelf region with high nutrient supply. Episode IV (Oxfordian), Lenticulina bulla assemblage thrived in hyposaline conditions with low oxygen levels and enough nutrients in the deeper portion of the mid-shelf region. An unstable oceanic shelf is interpreted during the deposition of the examined section because of the fluctuations in all inferred parameters.

Local And Deep-Ocean Forcing Effects on the West Florida Continental Shelf Circulation and Ecology

We review the evolution of knowledge on the forcing of the west Florida continental shelf by a combination of local winds and deep-ocean influences, and we provide application examples regarding the relationships between the shelf responses to these forcing functions and certain ecological phenomena, including blooms of the harmful alga,Karenia brevis, recruitment of gag juveniles and how Deepwater Horizon hydrocarbons may have affected west Florida reef fish and the shoreline. Our approach employs a coordinated set of observations and numerical circulation model simulations, wherein the observations, by providing reasonable veracity checks on the model simulations, allow for further dynamical analyses that would otherwise be unavailable from the observations alone. For the case of local forcing only, we provide two dynamically consistent definitions of the inner-shelf and outer-shelf regions, and for the case of deep-ocean forcing, we show how the west Florida shelf geometry (with regard to certain geophysical fluid dynamics principles) can result in the entire shelf region being impacted by the Gulf of Mexico Loop Current. Thus, we help to explain why the west Florida shelf experiences large inter-annual variations in shelf ecology, providing impetus for further interdisciplinary study.

Interactions between the North Brazilian Undercurrent (NBUC) and the Southwest Atlantic Margin. Implications for Brazilian shelf-edge systems

Western boundary currents influence the global ocean circulation and climate, whereas it locally reaches out differently to the continental margins. This study investigates the response of the North Brazilian Undercurrent (NBUC) over their interactions with the eastern and northern margins of the northeastern Brazil. The data set comprises regional bathymetry, in situ current measurements, CTD profiling, and simulations of oceanic currents using a regional model (CROCO). The physical analysis focuses on the months of February (austral summer) and August (austral winter). Horizontal and vertical structure of current velocity, temperature and salinity were correlated using maps and bathymetric profiles along the critical pathways of the NBUC. The eastern and northern margins are narrow and retracted with widths up to 40 km and steep upper continental slopes (14°). These margins are separated by the Touros High, which extends eastward up to 80 km offshore, with a shallow shelf (most parts are < 10 m) of approximately 55 km wide. The vertical sections of velocity show the NBUC shifting onto the Touros shelf in August and show that the strong trade winds during the austral winter handle the alongshore current circulation of this region. In the northern margin, the recirculation of the NBUC disturbs the base of the thermocline and part of these current fluxes toward the outer shelf region. The different patterns of the NBUC affect the sedimentary and ecological characteristics of eastern, Touros and northern outer shelves. Besides, the slope and outer shelf morphology might contribute to events of current-driven nutrient-enrichment and mixing processes at the base of the mixed layer. These results support the evidences that the western boundary current interactions by eddies and jets with the margin control the morpho-sedimentary and environmental conditions of the Brazilian outer shelf ecological system corridor.

Sediment Prediction in the Great Barrier Reef using Vision Transformer with finite element analysis

Suspended sediment is a significant threat to the Great Barrier Reef (GBR) ecosystem. This catchment pollutant stems primarily from terrestrial soil erosion. Bulk masses of sediments have potential to propagate from river plumes into the mid-shelf and outer-shelf regions. Existing sediment forecasting methods suffer from the problem of low-resolution predictions, making them unsuitable for wide area coverage. In this paper, a novel sediment distribution prediction model is proposed to augment existing water quality management programs for the GBR. This model is based on the state-of-the-art Transformer network in conjunction with the well-known finite element analysis. For model training, the emerging physics-informed neural network is employed to incorporate both simulated and measured sediment data. Our proposed Finite Element Transformer (FE-Transformer) model offers accurate predictions of sediment across the entire GBR. It provides unblurred outputs, which cannot be achieved with previous next-frame prediction models. This paves a way for accurate forecasting of sediment, which in turn may lead to improved water quality management for the GBR.

Temporal changes of phytoplankton biomass in the western Black Sea shelf waters: Evaluation by satellite data (1998–2018)

This study investigated temporal changes of phytoplankton biomass with particular focus on blooms and their underlying mechanisms within different shelf regions in the western part of the Black Sea for the poorly studied post-eutrophication period. We combined satellite chlorophyll with carbon-to-Chl a ratios to obtain a better proxy of phytoplankton biomass, and applied an algorithm to partition these data into a base seasonal variation and blooms. The base phytoplankton biomass was characterized by a seasonal maximum in October–November, highest values in the Romanian inner shelf region that receives inputs directly from the Danube River, and downward time trends in all shelf regions, coinciding with reduced nitrate inputs from the Danube. The majority of phytoplankton blooms were short-lived events (lasting up to 5 days), which accounted for over 60% of total bloom events. The initiation of spring blooms coincided with the peak riverine input for the Romanian inner shelf and with the formation of the thermocline in other regions. Autumn blooms were observed with the breakdown of the thermocline in October–November. These were most likely sustained by nutrient accumulation in bottom waters originating from riverine inputs in spring and regenerated nutrients from sedimenting organic matter and sediments. Large diatoms may contribute to autumn blooms in the outer shelf regions through harvesting “new” nitrate from deeper waters and hosting endosymbiotic cyanobacteria to extract “new” nitrogen from the atmosphere. Finally, high intensity of upwelling processes could support winter blooms in the Bulgarian outer shelf region.

Manned submersible dives reveal a singular assemblage of Hexactinellida (Porifera) off the Amazon River mouth, Northern Brazil.

The outer shelf and upper slope region under the influence of the Amazon River mouth harbors an extensive reef system with a rich sponge fauna, but no hexactinellids were recorded in the area so far. In this work, manned submersibles were used to describe for the first time three species of Hexactinellida off the Amazon River mouth: Hyalonema (Cyliconemaoida) alucia sp. nov., Dactylocalyx pumiceus and Claviscopulia facunda. We found two morphotypes of Dactylocalyx pumiceus, suggesting that it may be a complex of cryptic species. The populations of the three species off Par State were sparse, but a large aggregation of D. pumiceus was found off Maranho State from 145 to 230 m depth. These findings indicate that hexactinellid grounds may be more common along the Northern Brazilian continental outer shelf and slope than previously thought.

Three-Dimensional Movements and Habitat Selection of Young White Sharks (Carcharodon carcharias) Across a Temperate Continental Shelf Ecosystem

As highly mobile predators with extensive home ranges, some shark species often utilize a continuum of habitats across the continental shelf ranging from the surf zone to the open ocean. For many species, these cross-shelf distributions can change depending on ontogeny or seasonal conditions. Recent research has confirmed a white shark (Carcharodon carcharias) summer nursery off Long Island, New York; however, habitat characterization of this nursery has not yet been conducted nor has fine-scale analysis of vertical behavior. Between 2016 and 2019, 21 young-of-the-year and juvenile white sharks were fitted with satellite and acoustic tags to examine distribution and selection for a suite of oceanographic variables during their late summertime (i.e., August to October) residence in the New York Bight. Horizontal position estimates were used to extract a suite of environmental measurements via remote sensing platforms and were linked with vertical profiles to produce three-dimensional movements for a subset of individuals also fitted with pop-up satellite archival tags (n = 7). Sharks exhibited horizontal movements parallel to Long Island’s southern shoreline and coastal New Jersey, with distances from 0.1 to 131.5 km from shore. Log-likelihood chi-square analyses determined selection for waters with underlying bathymetry of 20–30 m, sea surface temperatures between 20.0 and 22.0°C, sea surface salinities between 31.0 and 32.0 ppt, and chlorophyll-a concentrations between 2.0 and 8.0 mg⋅m–3. Multiple individuals also traversed the mid- to outer shelf region after leaving the Montauk tagging area. Vertical depth profiles illustrated oscillations between the surface and 199 m of water, with an average swimming depth of 9.2 ± 8.9 m. Water column temperatures during these oscillations ranged between 7.9 and 26.2°C (mean = 19.5 ± 2.0°C) with several individuals traversing highly stratified regions presumably associated with a mid-shelf cold pool adjacent to the Hudson Shelf Valley. These results suggest young white sharks exhibit connectivity between the immediate shoreline and mid-continental shelf region, where they play important ecological roles as predators on a variety of species. Our study improves characterization of essential fish habitat for young white sharks and provides new insights into their reliance on this productive continental shelf ecosystem.

Reconstructing the Preindustrial Coastal Carbon Cycle Through a Global Ocean Circulation Model: Was the Global Continental Shelf Already Both Autotrophic and a CO2 Sink?

AbstractThe contribution of continental shelves to the marine carbon cycle is still poorly understood. Their preindustrial state is, for one, essentially unknown, which strongly limits the quantitative assessment of their anthropogenic perturbation. To date, approaches developed to investigate and quantify carbon fluxes on continental shelves have strongly simplified their physical and biogeochemical features. In this study, we enhance the global ocean biogeochemistry model HAMburg Ocean Carbon Cycle by explicitly representing riverine loads of carbon and nutrients, as well as improving the representation of organic matter dynamics in the coastal ocean. Our simulations, at a resolution of ∼0.4°, reveal a globally averaged shelf water residence time (RT) of 12–17 months, which is much shorter than the global RTs previously assumed in benchmark studies (&gt;4 years). This shorter global RT, induced primarily through outer shelf regions with large oceanic inflows, promotes an efficient offshore transport of terrestrial and marine organic carbon (0.44 PgCyr−1) and a dissolved inorganic carbon sink from the organic cycling of carbon on the global shelf (net ecosystem productivity [NEP] equal to +0.20 PgCyr−1). In turn, this autotrophic state of continental shelves contributes to a weak global preindustrial sink of atmospheric CO2 (0.04 PgCyr−1), dominated by extensive regions with large oceanic inflows and positive NEPs, such as the Patagonian shelf, the East China Sea and the outer North Sea. The contemporary global shelf CO2 uptake of 0.15 PgCyr−1 furthermoresuggests that the anthropogenic CO2 uptake (0.11 PgCyr−1) on the global continental shelf is less efficient with respect to the open ocean.

Subsurface Ocean Warming Hotspots and Potential Impacts on Marine Species: The Southwest South Atlantic Ocean Case Study

Fil: Franco, Barbara Cristie. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Oficina de Coordinacion Administrativa Ciudad Universitaria. Centro de Investigaciones del Mar y la Atmosfera. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Investigaciones del Mar y la Atmosfera; Argentina. Instituto Franco-argentino sobre Estudios del Clima y sus Impactos; Argentina

Nutrients and particulate organic matter dynamics in the outer-shelf of the South Brazil Bight: Two distinct scenarios during summer 2013

The pool of particulate organic matter driven by primary production in western boundary continental margins is known to be smaller than the highly eutrophic upwelling systems of eastern margins. Its production and export, however, can be high compared to productive ocean environments due to inherent specific physical dynamics such as mesoscale instabilities driven by the boundary current. To investigate how such physical process influence nutrients, chlorophyll-a and particulate matter on the outer shelf of the South Brazil Bight, two oceanographic cruises were conducted three months apart (November 2012 and January 2013), both under wind conditions that favor intrusions of South Atlantic Central Water (SACW). Our results showed two distinct hydrographic scenarios derived by the relative positions of oceanographic fronts in the outer shelf and shelf break region, associated with the Brazil Current (BC). In November 2012, the oligotrophic Tropical Water occupied a larger area of the continental shelf. Low nutrients and chlorophyll-a concentrations were found, typical of a regenerated production system. In contrast, maximum concentration of particulate matter and particulate inorganic carbon occurred at deeper layers in this period, together with low POC:PON ratio — probably from sediment resuspension. In January 2013, a strong shelf break upwelling was detected that enhanced SACW intrusion, notably increasing nutrient availability in the euphotic zone and the chlorophyll-a concentration at deeper layers. These deep chlorophyll maximum layers contribute to the production and accumulation of particulate organic carbon and nitrogen under these conditions. BC mesoscale instabilities appear to act as a particulate matter transport and export agent to the deep waters throughout the South Brazil Bight outer shelf.

Crustal structure of the offshore Labrador margin into deep water from combined seismic reflection interpretation and gravity modeling

A regional long-offset 2D seismic reflection program undertaken along the Labrador margin of the Labrador Sea, Canada, and complemented by the acquisition of coincident gravity data, has provided an extensive data set with which to image and model the sparsely investigated outer shelf, slope, and deepwater regions. Previous interpretation of the seismic data revealed the extent of Mesozoic and Cenozoic basins and resulted in the remapping of the basin configuration for the entire margin. To map the synrift package and improve understanding of the geometry and extent of these basins, we have undertaken joint seismic interpretation and gravity forward modeling to reduce uncertainty in the identification of the prerift basement, which varies between Paleozoic shelfal deposits and Precambrian crystalline rocks, with similar density characteristics. With this iterative approach, we have obtained new depth to basement constraints and have deduced further constraints on crustal thickness variations along the Labrador margin. At the crustal scale, extreme localized crustal thinning has been revealed along the southern and central portions of the Labrador margin, whereas a broad, margin-parallel zone of thicker crust has been detected outboard of the continental shelf along the northern Labrador margin. Our final gravity models suggest that Late Cretaceous rift packages from further south extend along the entire Labrador margin and open the possibility of a Late Cretaceous source rock fairway extending into the Labrador basins.

Vertical variations in the bio-optical properties of seawater in the northern South China Sea during summer 2008

Vertical variability in the bio-optical properties of seawater in the northern South China Sea (NSCS) including inherent optical properties (IOPs) and chlorophyll a concentration (Chl) were studied on the basis of in situ data collected in summer 2008 using an absorption/attenuation spectrophotometer. An empirical model was developed to estimate Chl profiles based on the absorption line height at long wavelengths, with a relative root mean square error of 37.03%. Bio-optical properties exhibited large horizontal and vertical spatial variability. As influenced by coastal upwelling and the Zhujiang River (Pearl River) discharge, both IOPs and Chl exhibited high values in the surface waters of the inner shelf, which tended to decrease with distance offshore. Subsurface maximum layers of IOPs and Chl were observed in the middle and outer shelf regions, along with significantly higher values of attenuation coefficients beneath this layer that rapidly increased towards the bottom. In the open ocean, both IOPs and Chl exhibited consistent variability, with the subsurface maximum layer typically located at 34–84 m. Phytoplankton were found to be one of the major components in determining the vertical variability of bio-optical properties, with their vertical dynamics influenced by both physical forcing and light attenuation effects. The depth of the subsurface maximum layer was found to be closely related to the fluctuation of the oceanic thermocline and the depth of the euphotic zone, which also affected the total integrated biomass of the upper ocean. Typically high values of attenuation coefficients observed in the bottom waters of the continental shelf reflected the transport of particulate matter over the bottom boundary layer. Our results reveal large spatial differences in bio-optical profiles in response to complex marine ecodynamics in the NSCS. From the perspective of marine research, high-resolution optical measurements are clearly advantageous over conventional bottle sampling.

Examining the ecological role of jellyfish in the Eastern Bering Sea

AbstractWithin the Eastern Bering Sea, the jellyfish Chrysaora melanaster has fluctuated widely over recent decades. We examined the role of C. melanaster as an ecosystem-structuring agent via application of ecosystem models representing inner-, mid-, and outer-shelf regions of comparable areal coverage. Chrysaora melanaster utilize 1% of total mid-shelf consumer production, or 1/4th the energy required by forage fish (capelin Mallotus villosus, Pacific herring Clupea pallasii, age-0 Pacific cod Gadus macrocephalus, age-0 walleye pollock Gadus chalcogrammus). Model simulations show the impacts of C. melanaster are broadly distributed across consumer groups with increasingly negative impacts with higher jellyfish biomass. Age-0 pollock represent the greater part of the forage fish biomass, and observed pollock biomass during low jellyfish years (2004–2007) was significantly greater than during high jellyfish years (2009–2014). However, sensitivity among consumer groups to observed jellyfish variability is small, within 5% of baseline (2004–2015) conditions. Estimates using similar models for the Coastal Gulf of Alaska (CGoA) and Northern California Current (NCC) suggest large differences in the role of scyphozoans among northern Pacific shelf ecosystems. Only 0.1% of total summer consumer production is required to support CGoA Chrysaora, while the coastal NCC population uses 19%.

Multispecies biomass dynamics models reveal effects of ocean temperature on predation of juvenile pollock in the eastern Bering Sea

AbstractWalleye pollock (Gadus chalcogrammus) supports one of the largest commercial fisheries in the world. Juvenile pollock are important forage fish in the eastern Bering Sea (EBS) ecosystem, often representing the largest fraction in the diets of major Bering Sea piscivores. Large variability in the EBS pollock stock biomass in recent years has been attributed primarily to fluctuations in recruitment. It has been hypothesized that predation rates on forage fishes increase when the cold pool (a body of cold water &lt; 2°C) is extensive and covers much of the middle continental shelf, which tends to concentrate larger predatory fishes in the outer shelf and slope regions. In contrast, young pollock appear to tolerate colder temperatures than older fish and can stay in the cold pool, thereby reducing predation. We used a multispecies modeling approach to examine the effects of the cold pool size on predation of juvenile pollock. We found that predation on age‐1 pollock by age‐3+ pollock decreased, and predation on age‐1 and age‐2 pollock by arrowtooth flounder increased with increasing bottom temperature, which was used as a proxy for the cold pool size. These results suggest that the cold pool creates spatial separation between juvenile pollock and arrowtooth flounder, but not between adult and juvenile pollock. The model developed in this study could be used to examine the effects of other covariates on interspecific interactions, help explain observed changes in fish communities, and understand implications of climate change on ecosystems and their productivity.

Dissolved organic carbon dynamics in the East China Sea and the northwest Pacific Ocean

Abstract. Oceanic dissolved organic carbon (DOC) represents one of the largest carbon reservoirs on Earth, and its distribution and biogeochemical cycles play important roles in carbon cycling and other biogeochemical processes in the ocean. We report the distribution and concentrations of DOC for water samples collected from the shelf-edge and slope regions in the East China Sea (ECS) and the Kuroshio Extension (KE) in the northwestern North Pacific during two cruises in 2014–2015. The DOC concentrations were 45–88 µM in the ECS and 35–65 µM in the KE. In addition to biological processes that are estimated to account for 7 % and 8 %–20 % in shaping the DOC distribution in the ECS and KE regions, respectively, the DOC distribution is largely controlled by hydrodynamic mixing of different water masses. By comparing the DOC results with dissolved inorganic carbon (DIC) and dissolved inorganic radiocarbon (Δ14C-DIC) measured from the same water samples, we further demonstrate that the intrusion of the Kuroshio Current could dilute the DOC concentrations at stations in the outer shelf and slope regions of the ECS. The concentrations of DOC in the KE were significantly lower in surface waters than in the ECS, and a relatively low and stable DOC level (∼40 µM) was found in deep water (below 1500 m) at all stations. Based on the previously reported DIC and Δ14C-DIC values for the stations, the observed spatial variations of DOC in the upper 700 m among the stations in the KE were mainly influenced by mixing of the two water masses carried by the Kuroshio and Oyashio, the two dominant western boundary currents in the region. The hydrodynamic processes are thus important factors in the distribution and dynamics of DOC in the KE region.

Geochemistry and Sedimentary Sources of the Surface Sediments from the Continental Shelf off the Indus Delta, Pakistan

This study focuses on the spatial distribution of the major and minor elements (Al, Ca, Fe, K, Ti, Ba, Sr, V, Zn, Cr, Ni, Li, Zr, Cu, and Co) and the textural characteristics of the surface sediments from the continental shelf off the Indus delta, Pakistan. The sediments from the inner shelf near the Indus River mouth and around the Indus canyon towards the outer shelf region are fine-grained clayey silt with low (~30%) carbonate. The coarse-grained sediments, high (40–70%) in carbonate with abundant skeletal material cover the western shelf area. The inter-element relationship, elements distribution, and associated textural characteristics of the sediments suggest a common detrital source except for Ca. The concentration of the major elements (Al, Fe, K and Ti) and the trace elements (Ba, V, Zn, Cr, Ni, Li, Zr, Cu, and Co) is highest in the silty clayey sediments from the inner shelf and near the Indus River mouth, around the Indus canyon and towards the outer shelf region. The Indus River sediments are the major contributing source of these elements. A relatively high concentration of Cr, Zr, Ni, Zn and Cu in the sediments from the western shelf area imply a source different from the major Indus River probably from the western Makran or Murray ridge zone. Association of Ca and Sr with CaCO3 in the western and central west area of the Indus shelf suggests that calcareous skeletal fragments are the main contributor of these elements in the surface sediments that contain 40–70% carbonate.