Continental Shelf Region Research Articles

Diversity Distribution, Driving Factors and Assembly Mechanisms of Free-Living and Particle-Associated Bacterial Communities at a Subtropical Marginal Sea.

Free-living (FL) and particle-associated (PA) bacterioplankton communities play critical roles in biogeochemical cycles in the ocean. However, their community composition, assembly process and functions in the continental shelf and slope regions are poorly understood. Based on 16S rRNA gene amplicon sequencing, we investigated bacterial communities’ driving factors, assembly processes and functional potentials at a subtropical marginal sea. The bacterioplankton community showed specific distribution patterns with respect to lifestyle (free living vs. particle associated), habitat (slope vs. shelf) and depth (surface vs. DCM and Bottom). Salinity and water temperature were the key factors modulating turnover in the FL community, whereas nitrite, silicate and phosphate were the key factors for the PA community. Model analyses revealed that stochastic processes outweighed deterministic processes and had stronger influences on PA than FL. Homogeneous selection (Hos) was more responsible for the assembly and turnover of FL, while drift and dispersal limitation contributed more to the assembly of PA. Importantly, the primary contributor to Hos in PA was Gammaproteobacteria:Others, whereas that in FL was Cyanobacteria:Bin6. Finally, the PICRUSt2 analysis indicated that the potential metabolisms of carbohydrates, cofactors, amino acids, terpenoids, polyketides, lipids and antibiotic resistance were markedly enriched in PA than FL.

Fortnightly Variation of the Tsushima Warm Current on the Continental Shelf in the Southwestern Japan Sea

AbstractThe first and second branches of the Tsushima Warm Current flow on the continental shelf and along the shelf break/slope in the southwestern Japan Sea, respectively. The second branch corresponds to the offshore side of the bottom temperature front between the offshore cold and nearshore warm waters. Across the Tsushima Warm Current on the continental shelf and the shelf edge, five bottom‐mounted ADCPs with temperature sensors were deployed between middle June and late July 2014. At the shelf edge, the bottom temperature varied with the diurnal tidal cycle. The offshore bottom cold‐water intruded into the continental shelf region in conjunction with the fortnightly spring‐neap (2‐week) cycle which is the modulation of the diurnal K1 and O1 internal tides. The bottom temperature front and the first branch of the Tsushima Warm Current on the continental shelf intensified in response to the bottom cold‐water intrusion.

Optimization and assessment of phytoplankton size class algorithms for ocean color data on the Northeast U.S. continental shelf

The size structure of phytoplankton communities influences important ecological and biogeochemical processes, including the transfer of energy through marine food webs. A variety of algorithms have been developed to estimate phytoplankton size classes (PSCs) from satellite ocean color data. However, many of these algorithms were developed for application to the global ocean, and their performance in more productive, optically complex coastal and continental shelf regions warrants evaluation. In this study, several existing PSC models were applied in the Northeast U.S. continental shelf (NES) region and compared with in situ PSC estimates derived from a local HPLC pigment data set. The effect of regional re-parameterization and incorporation of sea surface temperature (SST) into existing abundance-based model frameworks was investigated and model performance was assessed using an independent data set. Abundance-based model re-parameterization alone did not result in significant improvement in model performance compared with other models. However, the inclusion of SST led to a consistent reduction in model error for all size classes. Of two absorption-based algorithms tested, the best performing approach displayed similar performance metrics to the regional SST-dependent abundance-based model. The SST-dependent model and the absorption-based method were applied to monthly composites of the NES region for April and September 2019 and qualitatively compared. The results highlight the benefit of considering SST in abundance-based models and the applicability of absorption-based PSC methods in optically complex regions.

Precursor arrivals of explosive sounds during the Seabed Characterization Experiment 2021

Travel time and amplitude of precursor arrivals of explosive sounds in shallow water contain information of marine sediments and could be used for geoacoustic inversion. The precursor arrivals have been identified in the received signals from explosive SUS charges detonated during the Seabed Characterization Experiment (SBCEX2021) conducted in the New England continental shelf and slope region in the summer of 2021. These SUS charges were deployed at various ranges along and across 200-m and 250-m bathymetry contours and recorded by two vertical line arrays (VLAs) positioned at 200-m and 250-m water depths. In addition to the two acoustic VLAs equipped with environmental sensors, there were three environmental moorings simultaneously capturing the water column fluctuation of temperature and salinity. In this research, measured precursor arrivals are first extracted and analyzed. Simulated results are then obtained and compared with the measured ones. Finally, a sensitivity study of the precursor arrivals on water column sound speed and sediment parameters (e.g., sound speed and attenuation) is performed. [Work supported by ONR Ocean Acoustics.]

Mid- to late-Holocene analysis of the influence of the La Plata River plume on the southwestern Atlantic shelf: A paleoenvironmental reconstruction based on lipid biomarkers and benthic foraminifera

A combined analysis of sedimentological, molecular, and microfossil proxies was used to determine paleoclimatic and paleoceanographic variations and assess sediment transport pathways along the last c.a. 6300 years in a sedimentary record collected on the inner shelf of the southwestern Atlantic Ocean. The combined use of terrestrial and marine proxies enables a more complete environmental perspective of the La Plata River plume influence on the southwestern Atlantic shelf, regarding the relationship between climate, productivity, as well as hydrodynamic. Variations in marine productivity, lipid biomarkers of terrestrial plants, diagnostic geochemical indices, and sea-surface temperature point to three phases within the core. The first interval (6300–5200 cal yr BP) was characterized by low marine and terrigenous organic matter input, with pulses of phytodetritus indicated by benthic foraminifera. These features suggested dry climatic conditions over the southeastern portion of South America, with the influence of sediments from the adjacent continent and, on a smaller scale, transported from the Argentinian shelf due to the high relative sea level. The second interval (5200–2800 cal yr BP) was distinguished by a slight increase in marine productivity and terrigenous input, indicating a transition period with an increase of total rainfall influenced by an intensified South American Monsoon System (SAMS) and the modern El Niño-Southern Oscillation (ENSO) phenomenon. These features, associated with the changes in wind patterns and the lower relative sea level, suggest the onset of the influence of the La Plata River (LPR) plume over the southern regions of the Brazilian continental shelf for the last 6300 cal yr BP. The last interval (2800–890 cal yr BP) had the highest contents of marine and terrigenous proxies, suggesting less climatic variability, as the long-term intensification of the SAMS and a further increase in the amplitude of the ENSO resulted in the modern establishment and dominant influence of the LPR plume on the core site. Variations in sea-surface temperature up to 3.3°C were related to the influence of the LPR plume on the shelf off southern Brazil.

Global Connectivity of Southern Ocean Ecosystems

Southern Ocean ecosystems are globally important. Processes in the Antarctic atmosphere, cryosphere, and the Southern Ocean directly influence global atmospheric and oceanic systems. Southern Ocean biogeochemistry has also been shown to have global importance. In contrast, ocean ecological processes are often seen as largely separate from the rest of the global system. In this paper, we consider the degree of ecological connectivity at different trophic levels, linking Southern Ocean ecosystems with the global ocean, and their importance not only for the regional ecosystem but also the wider Earth system. We also consider the human system connections, including the role of Southern Ocean ecosystems in supporting society, culture, and economy in many nations, influencing public and political views and hence policy. Rather than Southern Ocean ecosystems being defined by barriers at particular oceanic fronts, ecological changes are gradual due to cross-front exchanges involving oceanographic processes and organism movement. Millions of seabirds and hundreds of thousands of cetaceans move north out of polar waters in the austral autumn interacting in food webs across the Southern Hemisphere, and a few species cross the equator. A number of species migrate into the east and west ocean-basin boundary current and continental shelf regions of the major southern continents. Human travel in and out of the Southern Ocean region includes fisheries, tourism, and scientific vessels in all ocean sectors. These operations arise from many nations, particularly in the Northern Hemisphere, and are important in local communities as well as national economic, scientific, and political activities. As a result of the extensive connectivity, future changes in Southern Ocean ecosystems will have consequences throughout the Earth system, affecting ecosystem services with socio-economic impacts throughout the world. The high level of connectivity also means that changes and policy decisions in marine ecosystems outside the Southern Ocean have consequences for ecosystems south of the Antarctic Polar Front. Knowledge of Southern Ocean ecosystems and their global connectivity is critical for interpreting current change, projecting future change impacts, and identifying integrated strategies for conserving and managing both the Southern Ocean and the broader Earth system.

Effect of Summer Typhoon Linfa on the Chlorophyll-a Concentration in the Continental Shelf Region of Northern South China Sea

Based on both physical and biological data collected from multi-source satellite during summer typhoon Linfa, we found that the typhoon triggered two phytoplankton declines and three phytoplankton blooms in the northern South China Sea (SCS), where the waters were influenced by coastal upwelling and the input of terrigenous materials from the Pearl River estuary (PRE). One phytoplankton decline (about a 3-fold reduction) in the continental shelf region can probably be attribute to the limited nutrient supply induced by the decayed coastal northeastern current and onshore Ekman transport (OET) and Kuroshio intrusion water, as well as the uplifted subsurface’s low chlorophyll-a (Chl-a) concentration driven by vertical mixing and upwelling. Another phytoplankton decline (about a 3.5-fold reduction) in the eastern Leizhou Peninsula-coastal upwelling region is probably caused by OET and a decayed coastal northern current. Conversely, the decayed coastal current, OET, and the vertical mixing and upwelling could lead to the transport of nutrient-rich water from the PRE to the nearshore region of the southwestern PRE mouth, and from the subsurface layer to the surface, respectively, thereby stimulating the growth of phytoplankton in the nearshore region (increased by about 4-fold) and the open ocean (increased by about 2.3-fold). In the Shantou (the coastal upwelling region), the phytoplankton responses to nutrient supply were feeble when phytoplankton was already growing in nutrient replete conditions. In addition, the OET and the high turbidity barely resulted in moderate phytoplankton bloom (increased by 38%). In summary, the physical driving forces associated with typhoons that modulates phytoplankton dynamics are the nutrient and phytoplankton transportation in the northern SCS during the wet season.

Wave–current-surge interaction in a changing climate over a shallow continental shelf region

Wave climate over the North Indian Ocean region experienced a paradigm shift in the recent past, indicating an increase in the extremes. Wind-waves and swell climatology have shown an increasing trend over this region, having direct implications on the coastal zone dynamics surrounding the mainland and island features. The present study aims to investigate the wave–current-surge interaction characteristics over a shallow continental shelf region between India and Sri Lanka using the state-of-art coupled ADCIRC-SWAN model. In particular, a case study performed during tropical cyclone Madi (2013) demonstrates the extreme wave–current-surge interaction mechanism over varying nearshore bathymetric features. Study investigated the wave reflection and transmission characteristics in both the absence and presence of the proposed navigation channel (known as Sethusamudram project) in a coastal vulnerability context. Construction of the channel may result in westward shift of hazardous coastal water zones attributed to storm tides. The navigation channel expects to enhance both extreme waves and storm surge by 1% and 4%, respectively. Synthetic experiments, considering an increase in sea level rise by 0.4 m expected by 2050, indicate that wave activity can increase by 3% with marginal variations in storm tide. Simulations performed with a 7% rise in tropical cyclone intensity reveals a substantial increase in storm surge (10%) and significant wave (20%) heights along the coastal belt.

A chemical weathering control on the delivery of particulate iron to the continental shelf

The delivery of potentially reactive iron minerals to the marine environment exerts a major control on ocean and marine sediment biogeochemistry, including the preservation and burial of organic carbon. One aspect of the global iron cycle that has received little attention concerns the phase partitioning of iron in highly chemically-weathered sediments from (sub)tropical mountainous regions, where the sediment is commonly deposited directly onto adjacent continental margins. Here, we report the phase partitioning of particulate iron in surface seafloor sediments deposited from oxic bottom waters along the east coast of China, including the Bohai Sea, Yellow Sea and East China Sea, in addition to the continental shelf region adjacent to the (sub)tropical mountainous island of Hainan in the northern South China Sea. We document highly reactive (FeHR) to total iron (FeT) ratios for the Bohai Sea, Yellow Sea and East China Sea that are typical of global marine sediments deposited under oxic water column conditions. By contrast, FeHR/FeT ratios in Hainan offshore sediments are significantly elevated above normal oxic marine sediments. These Hainan offshore sediments display a strong positive correlation between FeHR/FeT ratios and the chemical index of alteration (CIA) weathering proxy, suggesting that the Fe speciation systematics are controlled by the intensity of chemical weathering. This observation is supported by additional geochemical data and Nd isotope analyses, which suggest a common source lithology for all the studied regions. The Hainan sediments thus document a specific scenario, whereby highly chemically weathered sediments from the mountainous Hainan region bypass the inner shore settings that commonly disproportionately trap Fe (oxyhydr)oxide minerals, depositing high concentrations of FeHR on the adjacent continental margin. Such enrichments likely aid in the preservation of organic carbon in marine sediments, suggesting that organic carbon preservation and burial may be enhanced by elevated FeHR in such settings. We also establish a set of essential criteria for potential recognition of chemical weathering-induced enrichments in FeHR/FeT ratios in ancient marine sediments.

Diatom Hotspots Driven by Western Boundary Current Instability

AbstractClimatic changes have decreased the stability of the Gulf Stream (GS), increasing the frequency at which its meanders interact with the Mid‐Atlantic Bight (MAB) continental shelf and slope region. These intrusions are thought to suppress biological productivity by transporting low‐nutrient water to the otherwise productive shelf edge region. Here we present evidence of widespread, anomalously intense subsurface diatom hotspots in the MAB slope sea that likely resulted from a GS intrusion in July 2019. The hotspots (at ∼50 m) were associated with water mass properties characteristic of GS water (∼100 m); it is probable that the hotspots resulted from the upwelling of GS water during its transport into the slope sea, likely by a GS meander directly intruding onto the continental slope east of where the hotspots were observed. Further work is required to unravel how increasingly frequent direct GS intrusions could influence MAB marine ecosystems.

A Multifaceted Approach to Advance Oil Spill Modeling and Physical Oceanographic Research at the United States Bureau of Ocean Energy Management

The Environmental Studies Program (ESP) at the United States Bureau of Ocean Energy Management (BOEM) is funded by the United States Congress to support BOEM’s mission, which is to use the best available science to responsibly manage the development of the Nation’s offshore energy and mineral resources. Since its inception in 1973, the ESP has funded over $1 billion of multidisciplinary research across four main regions of the United States Outer Continental Shelf: Gulf of Mexico, Atlantic, Alaska, and Pacific. Understanding the dynamics of oil spills and their potential effects on the environment has been one of the primary goals of BOEM’s funding efforts. To this end, BOEM’s ESP continues to support research that improves oil spill modeling by advancing our understanding and the application of meteorological and oceanographic processes to improve oil spill modeling. Following the Deepwater Horizon oil spill in 2010, BOEM has invested approximately $28 million on relevant projects resulting in 73 peer-reviewed journal articles and 42 technical reports. This study describes the findings of these projects, along with the lessons learned and research information needs identified. Additionally, this paper presents a path forward for BOEM’s oil spill modeling and physical oceanographic research.

Impact of larval behaviors on dispersal and connectivity of sea scallop larvae over the northeast U.S. shelf

Sea scallops (Placopecten magellanicus) are a highly fecund species that supports one of the most commercially valuable fisheries in the northeast U.S. continental shelf region. Scallop landings exhibit significant interannual variability, with abundances widely varied due to a combination of anthropogenic and natural factors. By coupling a pelagic-stage Individual-Based scallop population dynamics Model (hereafter referred to as Scallop-IBM) with the Northeast Coastal Ocean Forecast System (NECOFS) and considering the persistent aggregations over Georges Bank (GB)/Great South Channel (GSC) as source beds, we have examined the dispersion and settlement of scallop larvae over 1978–2016. The results demonstrated that the significant interannual variability of larval dispersal was driven by biophysical interactions associated with scallop larval swimming behaviors in their early stages. The duration, frequency, and stimulus of larval vertical migration in the ocean mixed layer (OML) affected the residence time of larvae in the water column over GB. It thus sustained the persistent aggregations of scallops in the GB/GSC and Southern New England region. In addition to larval behavior in the OML, the larval transport to the Middle Atlantic Bight (MAB) was also closely related to the intensity and duration of northeasterly wind in autumn. There was no conspicuous connectivity of scallop larvae between GB/GSC and MAB in the past 39 years except in the autumn of 2009. In 2009, the significant larval transport to the MAB was produced by unusually strong northeasterly winds. Ignoring larval behavior in the OML could overestimate the scallop population’s connectivity between GB and the MAB and thus provide an unrealistic prediction of scallop larval recruitment in the region. Both satellite-derived SST and NECOFS show that the northeast U.S. shelf experienced climate change-induced warming. The extreme warming at the shelfbreak off GB tends to intensify the cross-isobath water temperature gradient and enhance the clockwise subtidal gyre over GB. This change can increase the larval retention rate over GB/GSC, facilitating enhanced productivity on GB.

Projected shifts in loggerhead sea turtle thermal habitat in the Northwest Atlantic Ocean due to climate change

It is well established that sea turtles are vulnerable to atmospheric and oceanographic shifts associated with climate change. However, few studies have formally projected how their seasonal marine habitat may shift in response to warming ocean temperatures. Here we used a high-resolution global climate model and a large satellite tagging dataset to project changes in the future distribution of suitable thermal habitat for loggerheads along the northeastern continental shelf of the United States. Between 2009 and 2018, we deployed 196 satellite tags on loggerheads within the Middle Atlantic Bight (MAB) of the Northwest Atlantic continental shelf region, a seasonal foraging area. Tag location data combined with depth and remotely sensed sea surface temperature (SST) were used to characterize the species’ current thermal range in the MAB. The best-fitting model indicated that the habitat envelope for tagged loggerheads consisted of SST ranging from 11.0° to 29.7 °C and depths between 0 and 105.0 m. The calculated core bathythermal range consisted of SSTs between 15.0° and 28.0 °C and depths between 8.0 and 92.0 m, with the highest probability of presence occurred in regions with SST between 17.7° and 25.3 °C and at depths between 26.1 and 74.2 m. This model was then forced by a high-resolution global climate model under a doubling of atmospheric CO2 to project loggerhead probability of presence over the next 80 years. Our results suggest that loggerhead thermal habitat and seasonal duration will likely increase in northern regions of the NW Atlantic shelf. This change in spatiotemporal range for sea turtles in a region of high anthropogenic use may prompt adjustments to the localized protected species conservation measures.

Range edges of North American marine species are tracking temperature over decades.

Understanding the dynamics of species range edges in the modern era is key to addressing fundamental biogeographic questions about abiotic and biotic drivers of species distributions. Range edges are where colonization and extirpation processes unfold, and so these dynamics are also important to understand for effective natural resource management and conservation. However, few studies to date have analyzed time series of range edge positions in the context of climate change, in part because range edges are difficult to detect. We first quantified positions for 165 range edges of marine fishes and invertebrates from three U.S. continental shelf regions using up to five decades of survey data and a spatiotemporal model to account for sampling and measurement variability. We then analyzed whether those range edges maintained their edge thermal niche-the temperatures found at the range edge position-over time. A large majority of range edges (88%) maintained either summer or winter temperature extremes at the range edge over the study period, and most maintained both (76%), although not all of those range edges shifted in space. However, we also found numerous range edges-particularly poleward edges and edges in the region that experienced the most warming-that did not shift at all, shifted further than predicted by temperature alone, or shifted opposite the direction expected, underscoring the multiplicity of factors that drive changes in range edge positions. This study suggests that range edges of temperate marine species have largely maintained the same edge thermal niche during periods of rapid change and provides a blueprint for testing whether and to what degree species range edges track temperature in general.

Introduction and application of a proposed method for quantitative soundscape analysis: The soundscape code

A novel methodology for the analysis of soundscapes was developed in an attempt to facilitate quick and accurate soundscape comparisons across time and space. The methodology, proposed here for the first time, consists of a collection of traditional soundscape metrics, statistical measures, and acoustic indices that were selected to quantify several salient properties of marine soundscapes: amplitude, impulsiveness, periodicity, and uniformity. The metrics were calculated over approximately 30 h of semi-continuous passive acoustic data gathered in seven unique acoustic environments. The resultant metric values were analyzed and cross-examined to determine which combination most effectively captured the characteristics of the respective soundscapes. The best measures of amplitude, impulsiveness, periodicity, and uniformity were combined to form the proposed “Soundscape Code,” which allows for rapid multidimensional and direct comparisons of salient soundscape properties across time and space. The soundscape code methodology was then applied at three deep-sea habitats located in the Mid- South Atlantic Outer Continental Shelf (OCS) region that varied in depth, substrate, proximity to shore, and community structure. Soundscape code metrics highlighted nuanced differences in the acoustic environments and allowed for rapid, direct, quantitative comparisons to be made between the sites.

An observation-based evaluation and ranking of historical Earth system model simulations in the northwest North Atlantic Ocean

Abstract. Continental shelf regions in the ocean play an important role in the global cycling of carbon and nutrients, but their responses to global change are understudied. Global Earth system models (ESMs), as essential tools for building understanding of ocean biogeochemistry, are used extensively and routinely for projections of future climate states; however, their relatively coarse spatial resolution is likely not appropriate for accurately representing the complex patterns of circulation and elemental fluxes on the shelves along ocean margins. Here, we compared 29 ESMs used in the Intergovernmental Panel on Climate Change (IPCC)'s Assessment Reports (ARs) 5 and 6 and a regional biogeochemical model for the northwest North Atlantic (NWA) shelf to assess their ability to reproduce surface observations of temperature, salinity, nitrate and chlorophyll. The NWA region is biologically productive, influenced by the large-scale Gulf Stream and Labrador Current systems and particularly sensitive to climatically induced changes in large-scale circulation. Most ESMs compare relatively poorly to observed surface nitrate and chlorophyll and show differences with observed surface temperature and salinity that suggest spatial mismatches in their large-scale current systems. Model-simulated nitrate and chlorophyll compare better with available observations in AR6 than in AR5, but none of the models perform equally well for all four parameters. The ensemble means of all ESMs, and of the five best-performing ESMs, strongly underestimate observed chlorophyll and nitrate. The regional model has a much higher spatial resolution and reproduces the observations significantly better than any of the ESMs. It also simulates reasonably well vertically resolved observations from gliders and bi-monthly ship-based monitoring observations. A ranking of the ESMs indicates that only one ESM has good and consistent performance for all variables. An additional evaluation of the ESMs along the regional model boundaries shows larger variability but is generally consistent with the ranking on the shelf. Overall, 11 ESMs were deemed satisfactory for use in the NWA, either directly or for regional downscaling.

Bycatch of non-commercial batoids in the trawl fishery of south India: Status and conservation prerequisites

Bycatch of trawl fishery is a global concern and batoid fishes, including skates, rays and guitar fishes, are caught frequently as non-targeted species in commercial trawl fishery of India. While the commercial batoid species are documented separately in fishery data, a large number of non-commercial species do not form part of fishery data, even though many such species are listed as ‘Data Deficient’ in IUCN red list. A survey was conducted from July 2018 to June 2019 in the major harbours and landing centresof the south coasts of India to monitor the non-commercial batoid species in the trawl bycatch. Massive landings of non-commercial batoid species such as Torpedo sinuspersici, Narcine cf maculata, Orbiraja powelli Acroteriobatus variegatus and the occasional occurrence of Dipturus johannisdavisi, Benthobatis moresbyi, Narcine timlei and Plesiobatis daviesi have been recorded, besides the juveniles, sub-adults and few adults of commercial species Rhinobatos annandalei, Brevitrygon imbricata and Neotrygon indica from south India. The non-commercial batoids mainly inhabit continental shelf and slope regions of Indian coast where fishing pressure and efforts are high. When these k-selected species live in fishing zones with intense fishing pressure, data deficient species of batoids should be considered as threatened, and this paper discuss challenges in the sector, and forwards strategies for conserving non-targeted batoids.

Regional differences in seasonal variation of air–sea CO2 exchange in the Yellow Sea

Evidence suggests that the continental shelf CO2 influx rate might have increased globally during the past several decades. It remains a challenge to quantify air–sea CO2 fluxes in continental shelf regions and to understand their variations. The Yellow Sea on the western margin of the North Pacific represents one of the largest continental shelf regions. In this study, we conducted 10 carbonate surveying cruises between 2011 and 2018 that revealed regional differences in seasonal variation of surface fugacity of CO2 (fCO2) and air–sea CO2 fluxes on the Chinese side of the Yellow Sea. Results suggested that among various continental shelf CO2 sinks, the Yellow Sea represents one of the weakest marine CO2 absorbers. Despite the regionality of the study, we integrated spring/summer biological drawdown, summer/autumn vertical mixing, and universal warming/cooling and air–sea re-equilibration into an explanation of the seasonal variation in fCO2. These insights are fundamental to understanding sea surface carbonate chemistry in the Yellow Sea, and might help elucidate the biogeochemical controls of air–sea CO2 fluxes in other temperate seas.

A bio-optical model for the estimation of chlorophyll a using animal-borne instruments in an optically complex ecosystem

Studies using marine animals instrumented with biologging devices to estimate phytoplankton biomass have typically omitted continental shelf regions due to the confounding effects of optically active constituents other than phytoplankton present. The lack of algorithms for these regions is problematic, as they are some of the most biologically productive in the world and are often inhabited by the species of interest. We developed a bio-optical model to estimate chlorophyll a concentration (chl a) using light attenuation (LA) measured using a standard oceanographic instrument in an optically complex water body that is applicable to data collected by animal-borne devices. To achieve this, we conducted a replicated experiment to compare measurements made using time-depth-light recorders (TDLRs) to those of a standard oceanographic instrument (the HyperPro) in an adjacent water body, the Bedford Basin, Nova Scotia, Canada. Measurements of LA made by TDLRs were comparable to those of the HyperPro atdepth. The best supported bio-optical model for the estimation of chl a included both LA measured by the HyperPro and season as a fixed effect. The use of animal-borne devices to collect subsurface chl a data not only provides an opportunity to collect valuable oceanographic data but also allows for the exploration of broader ecological questions relating to the influence of primary productivity on the movement patterns of wide-ranging marine species.

Distribution and stoichiometry of Al, Mn, Fe, Co, Ni, Cu, Zn, Cd, and Pb in the East China Sea

The dissolved (d) and total dissolvable (td) trace metals were determined in seawater samples collected from the East China Sea (ECS). Labile particulate (lp) species was calculated as td minus d, and the sectional and vertical distributions of d and lp trace metals were evaluated. The surface concentrations of dAl, dCo, dNi, dCu, and dPb were higher in the continental shelf region than in the Kuroshio region. lpAl and lpFe were the dominant species below a depth of 400 m, and a strong positive correlation was observed between them in the Kuroshio region. The enrichment factor (EF) against crustal abundance was calculated for the purpose of estimating the origin of dMs in the ECS. The EF(dFe) was close to unity. These results suggest that both lpFe and dFe are dominated by crustal sources. The other elements had high EF, indicating significant contributions from other sources. EF(dPb) was close to the enrichment factor in aerosol, suggesting atmospheric input from anthropogenic sources. The dM/P ratios were calculated to investigate the validity of the extended Redfield ratio in the ECS. The Mn/P, Co/P, Cu/P, Zn/P, and Cd/P ratios in shallow water (< 200 m) were within the same order of magnitude as those in phytoplankton. In contrast, the Al/P and Fe/P ratios were, respectively, 27 and 213 times higher in phytoplankton compared to those in shallow water. These results suggest that dFe is a potential limiting factor for biological production, although it is not exhausted in surface water.