Northern Shelf Research Articles

A Paleo-Changjiang Delta Complex on the East China Sea Shelf Formed Some 30 ka Ago (at the MIS 3 Stage)

The distribution patterns of the paleo-Changjiang River deltas formed during the MIS 3 period before the last glacial maximum (LGM) contain important information about the deltaic deposits in response to climate and sea-level changes. However, so far, they are still poorly understood. Here, we reconstruct the stratigraphic and chronological framework of the deltaic system based on the analysis of 1835 km of high-resolution seismic profiles obtained from the northern East China Sea, together with a comparison with the research results from four existing boreholes and three groups of published seismic profiles from the study area. Within the strata from MIS 5 to MIS 1 that are preserved on the northern shelf of the East China Sea, we discovered a large-scale paleodeltaic complex formed during the MIS 3 period. During MIS 3, sea level dropped slowly; the paleodelta formed was large in scale and was distributed between water depths of 40 and 150 m. It is now directly exposed at the seabed at a depth of more than 100 m. The paleodelta had extended from the northwest to the southeast, with maximum thickness of the deposits around 55 m. The extensions in the east–west and south–north directions both exceeded 300 km, with a total area around 1.35 × 105 km2. Since the late Pleistocene, the tectonic structure beneath the East China Sea has been relatively stable. As such, sea-level fluctuations, sediment supply, and original topography were the main controlling factors for the development of the delta.

Fish assemblages at the Yermak Plateau and in northern Svalbard waters during the period 2012–2020

During several surveys covering the north-western and northern Svalbard waters, and the deeper Yermak Plateau north of Svalbard during the period 2012–2020, 291 standardized hauls with a demersal trawl were made. All fishes in the catches were identified to the lowest possible taxonomic level, mostly to species. In addition to the data generated from the trawl catches, bottom temperature, salinity, and depth were recorded at each trawl station. The eelpouts were the most species rich family, with 15 species, followed by codfishes and sculpins with six species each. The other 13 families were represented with one to four species each. Atlantic cod (Gadus morhua) dominated by weight in the catches, while polar cod (Boreogadus saida) dominated by numbers. In the deeper areas including the Yermak Plateau, Greenland halibut (Reinhardtius hippoglossoides) dominated by weight. Zoogeographically, 23 species were Arctic, 5 were Mainly Arctic, 4 Arctoboreal, 25 Mainly Boreal, 9 Boreal, and 2 Widely Distributed. The Arctic species dominated in the deeper areas (Yermak Plateau and slope > 500 m) and on the shallow eastern shelf, whereas the Mainly Boreal species dominated along the slope and on the western and northern shelves < 500 m. A hierarchical cluster analysis revealed three prominent station clusters consistent with the zoogeographical classifications which reflected the oceanographic conditions, water masses and sea ice. The hierarchical cluster analysis additionally separated the cold-water species into two groups consistent with the bathymetry of the region. Diet studies of Atlantic cod revealed that it mainly fed on hyperiids, and that its preferred food further south, capelin, was not prominent in the diet.Regional index terms: Northeast Atlantic, Fram Strait, Svalbard, Yermak Plateau.

Weak local upwelling may elevate the risks of harmful algal blooms and hypoxia in shallow waters during the warm season

Harmful algal blooms (HABs) and hypoxia, as common ecological disasters, are typically site-specific and recurrent, causing enduring environmental problems for coastal communities. Although these issues are often attributed to coastal eutrophication, in certain low-nutrient areas, such ecological disasters still frequently occur while the underlying cause is poorly understood. A prime example is the Qinhuangdao coastal waters in North China. This study intends to investigate the controlling factors of such incongruous ecological issues recurring in those low-nutrient areas with a case study of Qinhuangdao, utilizing numerical models and satellite observations. The result indicates that the weak tide-induced upwelling during summer creates favorable conditions (warm water with high transparency) for the occurrence of HABs and hypoxia in this region. It is due to that Qinhuangdao is precisely situated at the current amphidromic point of semi-diurnal tides, characterized by weak tide mixing. Likewise, the same story happens on the northern shelf of the Shandong Peninsula, where ecological problems are also prominent in China. The present study implies that shallow waters with weak local upwelling are susceptible to ecological issues during the warm season. This finding challenges the traditional view that strong-upwelling zones are more vulnerable to ecological disasters due to ample nutrient supply within the euphotic layer. It implies that tidal dynamics can greatly affect the vulnerability of coastal waters to ecological issues, which can be of significance to coastal management. Furthermore, the finding may have broader global applicability, given the ubiquity of tide-induced upwelling in various other coastal regions.

Geographic variation in population structure and grazing features of Calanus glacialis/marshallae in the Pacific Arctic Ocean

Calanus glacialis/marshallae is a dominant zooplankton species in the Pacific Arctic Ocean that is widely distributed in shelf areas, and it plays a vital role in connecting primary production to higher trophic levels. Its phenology is well adapted to hydrography, but there is little available information about regional and diel changes in population structure and grazing features. In this study, we investigated C. glacialis/marshallae during autumn 2019 in the Eastern and Northeastern Chukchi and Canadian basins to reveal geographic and diel variations in population structure, body size, grazing activity, and fatty acid composition. The abundance of C. glacialis/marshallae was found to be high on the slopes and low on the shelves. Body size (prosome length) was well described by the Bělehrádek equation combined with in-situ temperature throughout the sampling region. Cluster analyses based on hydrographic parameters were divided into four regions: southern shelf, northern shelf, slope, and basin. The southern shelf was dominated by copepodite stage five (C5) transported from the Bering Sea by Pacific waters. C4 and C5 were dominant on the northern shelf, suggesting that they grew slower than those on the southern shelf, and the populations also exhibited higher concentrations of fatty acids originating from dinoflagellates than those originating from the pan-Arctic Ocean, indicating low productivity in the region. The population on the slope had the highest abundance, C4 was dominant, and large amounts of diatom-derived eicosapentaenoic acid (EPA). These features are attributed to the upwelling of populations and nutrients that support diatom growth. In the basin, the early copepodite stages of composition were distinctly higher than those recorded in previous studies, because larger amounts of organisms flow into the region, resulting in more extended reproduction periods. In the basin, small and large forms of C5 were simultaneously found, and the small form exhibited a diel grazing activity pattern, but the large forms did not. These findings suggest their well adaptation in changing of the Pacific Arctic Ocean.

Composition and sources of suspended particles in the Pacific Arctic region

During the 6th (2014) and 7th (2016) Chinese Arctic Expedition (CHINARE), samples of suspended particulate matter (SPM) were collected from both surface (depth: <1.0 m) and subsurface (depth: approximately between 10 and 150 m) waters over the northern shelf of the Bering Sea and in the western Arctic Ocean. To investigate the distribution and sources of organic matter in both the surface water and the vertical profile, the concentration and stable carbon isotopic composition of SPM, particulate organic carbon (POC), and particulate nitrogen (only in surface water samples) were determined, and some particle samples were selected for examination using scanning electron microscopy. Results showed apparent geographical partitioning and temporal variation in both the concentration and the composition of SPM. Higher SPM concentrations were observed in nearshore, shelf break, and sea ice edge areas; the distribution of POC concentration displayed a similar pattern, with higher values found from the northern part of the Bering Shelf to southern parts of the Chukchi Shelf. In surface water, SPM mainly comprised clay and detrital minerals with higher POC contents, lighter δ13C values, and higher POC/PN ratios, indicating organic matter predominantly derived from terrestrial sources in areas south of St. Lawrence Island and north of 73°N. The downward trend of heavier δ13C values, together with reduction in clay and detrital minerals, suggests that vertical transport of SPM is hindered by stratification, resulting in transport of terrestrial materials toward northern basin areas. In the Chukchi Slope and Canada Basin areas, extremely light δ13C values (as low as −33.41‰ PDB) were mainly observed at depths of 20–60 m, where the Polar Mixed Layer (PML) intersects with the Upper Halocline Layer (UHL). Under the condition of low sea ice extent in 2016, the POC-δ13C values were heavier in the PML than in the UHL in the Chukchi Slope and Canada Basin areas. These findings provide insights into the sources, transport, and fate of organic matter in the Pacific Arctic region, which have important implications for understanding the biogeochemical cycles and ecosystem dynamics in this remote and rapidly changing environment.

Relict and Modern Sediments on the Continental Shelf of the Northern South China Sea: A Reconsideration

AbstractUnderstanding the temporal‐spatial patterns of modern and relict sediments is of importance for assessing changes in the Quaternary environment and sea‐level. Sedimentological and geochemical data is presented, along with in situ shell‐based accelerator mass spectrometry 14C ages of 30 samples from the surface sediments on the northern shelf of the South China Sea (NSSCS). The authors’ data show that the NSSCS surface sediments exhibit considerable diversity in composition. Modern sediments are primarily constrained to the NW inner shelf, which is fed by fluvial sands sourced from Coastal South China river systems and dominated by the Pearl River Estuary delivery. The transport and discharge of the terrestrial sediments to the NSSCS is highly influenced by the Guangdong Longshore Current and its secondary cyclonic eddies. Relict sediments dominated by well‐sorted, medium‐ and coarse‐grained sands were identified in the NW Shenhu and NW Dongsha areas of the outer NSSCS. The sedimentology and geochemistry of the relict sediments imply that they were deposited in a dry and cold environment either during the low sea levels of the late Pleistocene (∼40 ka) or the early Holocene (∼10 ka). To the east, the Taiwan Shoal and vicinity are dominated by a sand mixture, at which the relict sediments were reworked by terrigenous supply and modern hydrodynamic environment due to the compound action of the Guangdong Longshore Current, seasonal cyclones, and Kuroshio Intrusion. The present isobaths of ∼−90 m in the NSSCS might be the reflective of the early Holocene coastal delta or the last glacial maximum shoreline.

Taxonomic Structure and Diversity of Benthic Diatoms (Bacillariophyta) in the Northern Shelf of the Black Sea

The key role of benthic diatoms in coastal ecosystems highlights the relevance of studying their biodiversity and developing integrated biodiversity conservation measures. Benthic diatom richness in the northern part of the Black Sea was estimated based on both published data and our own data. The checklist of benthic diatoms includes 1100 species and intraspecific taxa, 953 species, 149 genera, 61 families, 32 orders, and 3 classes of Bacillariophyta. More than 280 species and intraspecific taxa, as well as 8 genera new to the diatom flora of the Black Sea and 7 species new to science, were revealed. An interregional analysis of the diversity of benthic Bacillariophyta along the coasts of Bulgaria, Romania, and Crimea, as well as the northwestern and northeastern parts of the Black Sea shelf, was carried out using the Taxonomic Distinctness Indices (TaxDI). The lowest TaxDI value for Crimea was closest to the average value expected for the Black Sea diatom flora, indicating a large proportion of polyspecies branches in the taxocene structure, which resulted in the maximum species richness (species/genus = 7) and led to a decrease in the vertical evenness of hierarchical tree. On the contrary, the highest TaxDI value was detected off the Romanian coast, which was caused by the significant proportion of mono- and oligospecies branches and minimal species saturation in the taxocene structure (species/genus = 4). We also identified some species with a high taxonomic exclusivity rank. If these species disappear, the entire architectonics of the Black Sea hierarchical tree of Bacillariophyta may be significantly altered. Such region-specific species are given the highest protection priority since they have great importance for gene pool conservation.

Circulation and Cross‐Shelf Exchanges in the Northern Shelf of the Southwestern Atlantic: Dynamics

AbstractThe strong interaction between the Brazil Current and the adjacent shelf is clearly visible in satellite‐derived products (sea surface temperature, salinity, and chlorophyll‐a concentration). Assessments of circulation features and cross‐shelf exchanges from these products are, however, limited to the surface layer. Here we analyze the regional circulation and dynamics using the results of a suite of process‐oriented, high‐resolution numerical experiments. Passive tracers and Lagrangian floats characterize the exchanges between the shelf and the open ocean, identifying regions of high variability, and assessing the contribution of small‐scale eddies to the cross‐shelf mass exchanges. We estimate that 0.2–0.4 Sv of the shelf transport variability between 34°S and 25°S comes from ocean internal variability which represents ∼50%–70% of the total variability. Between 25°S and 21°S, internal ocean variability represents more than 90% of the shelf transport variability. We find that generation of cyclonic eddies is more frequent (&gt;15% of the time) at the shelfbreak bights. The core of these eddies contains fresher, colder, and more nutrient‐rich shelf waters. Maps of satellite chlorophyll‐a concentration suggest that the horizontal and vertical exchanges of mass associated with these eddies are a critical element of the primary production cycle.

Evaluation of heterocyte glycolipids with a hexose sugar moiety for tracing terrestrial organic matter in the South China Sea

Heterocyte glycolipids (HGs) are biomarkers for N2-fixing heterocytous cyanobacteria (HCB). The hexose (hereafter C6) sugar moiety of HGs is produced by free-living HCB dominant in fresh and brackish waters, while the pentose moiety (hereafter C5) of HGs is found in endosymbiotic HCB associated with diatoms in tropical-subtropical marine waters. Therefore, C6 HGs detected in marine environments may indicate terrestrial organic matter (TOM) input, but this may be complicated by the fact that free-living HCB may be active over a wide salinity range. In this study, we evaluate C6 HGs and their fraction in total HGs, referred to as FHG, to trace TOM in the South China Sea (SCS) by analyzing a series of surface sediments from the Pearl River Estuary (PRE) to the open SCS, as well as suspended particular matters (SPM) in the euphotic zone of central SCS and a sediment core 17950-2 in the deep SCS. Our results showed that C6 HGs were abundant in the PRE sediments but almost absent in sediments or SPM from the northern shelf to the central SCS, leading us to conclude that free-living HCB producing C6 HGs are inactive in the modern ocean where salinity is >30. In the sediment core, C6 HGs and FHG showed a variation pattern similar to sea level changes during glacial-interglacial cycles, and the reconstructed sea surface salinity was above 32 throughout the cycles. Such a pattern was also evident in the records of branched to isoprenoid tetraether (BIT) index and detrital content from the same core. Thus, the modern distribution of C6 HGs and FHG, together with their downcore records in this study, demonstrates that C6 HGs and FHG are excellent for tracking TOM in tropical-subtropical marine environments.

Monitoring Sea Currents with Midrange Acoustic Backscattering

This paper is devoted to an acoustical method of measuring mesoscale sea and ocean currents. Due to the fact that such currents exhibit variability, long-term studies are of great interest. The aim of this study is to prepare a physical foundation to organize current measurements in an automated way using stationary mounted underwater echosounding systems. An acoustic system operating at a frequency of 1–3 kHz (lower than commercial frequencies) that is capable of sensing echo signals from natural inhomogeneities located at distances of 1 to 10 km was tested. The test was conducted during a two-week marine experiment on the northern shelf of the Black Sea. The acoustic system was mounted on a platform together with a weather station and other tools that provided reference values for further comparison. Scattering from moving particles, as well as from wind waves, provides a general opportunity for sensing of currents at remote points. Since most scatterers exist at a depth of at least 2 m or on the surface, the proposed sensing method is going specialized for currents in upper layers. However, analysis of Doppler spectra of the actual returning (reverberation) signal showed that this kind of scattering was mixed with bottom reverberation (which contains no additional frequency shift), and other signal distortions were present. Thus, we proposed a new method of signal processing that is aware of the regional environment. The described method is based on machine learning, namely on gradient boosting to build decision trees, which compute water current properties. Such a computational routine is preceded by an original acoustic signal feature extraction process. Finally, a precision of an order of magnitude was achieved, and a sensing distance of at least 2 km was proven as a result of this study carried out with available instruments.

Multiple mechanisms for chlorophyll a concentration variations in coastal upwelling regions: a case study east of Hainan Island in the South China Sea

Abstract. Using satellite observations from 2003 to 2020 and cruise observations from 2019 and 2021, this study reveals an unexpected minor role of upwelling in seasonal and interannual variations in chlorophyll a (Chl a) concentrations in the coastal upwelling region east of Hainan Island (UEH) in the northwestern South China Sea (NWSCS). The results show strong seasonal and interannual variability in the Chl a concentration in the core upwelling area of the UEH. Different from the strongest upwelling in summer, the Chl a concentration in the UEH area reaches a maximum of 1.18 mg m−3 in autumn and winter, with a minimum value of 0.74 mg m−3 in summer. The Chl a concentration in summer increases to as high as 1.0 mg m−3 with weak upwelling, whereas the maximum Chl a concentration in October increases to 2.5 mg m−3. The analysis of environmental factors shows that, compared to the limited effects of upwelling, the along-shelf coastal current from the northern shelf and the increased precipitation are crucially important to the Chl a concentration variation in the study area. These results provide new insights for predicting marine productivity in upwelling areas, i.e., multiple mechanisms, especially horizontal advection, should be considered in addition to the upwelling process.

Depositional history of the subaqueous delta off the southeastern coast of Korea during the post-glacial period

The distal mud deposit (DMD) of the Korea Strait Shelf, located along the southeastern coast of Korea and detached from the main sediment source, the mouth of the Nakdong River, is considered a subaqueous delta system. The complex spatiotemporal changes in the stratigraphic architecture of the DMD were reconstructed, based on combined seismic and sediment core data, according to the three stages of post-glacial sea-level rise. During the early transgressive stage (from ca. 19 to 10.9 ka), transgression occurred at a relatively deeper northern outer shelf of the DMD, where Unit A began to be deposited in an aggradational stratal stacking pattern. During the late transgressive stage (ca. 10.9 to 8 ka), further sea-level rise provided sufficient accommodation for DMD, but an insufficient sediment supply from the Nakdong River might have prevented sedimentation. At the highstand stage (ca. 8 ka to the present), the increased supply of suspended sediments from the Nakdong River coupled with the entrance of the Tsushima Warm Current through the Korea Strait may have enabled the along-shore lobate progradation of Unit B on the flat and wide southern shelf. After appoximately 2 ka, as Unit B proceeded into the narrow, steep northern shelf, it started to prograde in a shore-normal direction, controlled by a rapid downslope decrease in near-bed shear stress. Over the last 700 years, sediments have been actively deposited at the depocenter of the DMD by frequent storm surges during the summer season. The reconstructed depositional history of the DMD demonstrates the importance of the pre-existing shelf morphology, along-shore currents, and storm surges in offshore sediment transport for a subaqueous delta in a microtidal shelf with a relatively small riverine sediment load.

Intermittent Generation of Internal Solitary‐Like Waves on the Northern Shelf of the South China Sea

AbstractPredicting the occurrence of internal solitary‐like waves (ISWs) is important for parameterizing turbulent dissipation. ISWs in the northern South China Sea (SCS) are well understood to mainly originate from the Luzon Strait (LS). They are generally predictable due to their phase‐locked relation with tidal forcing in the LS. However, irregular occurrence of ISWs is noted from our 9‐day moored measurements on the SCS shelf. More energetic ISWs unexpectedly appeared during the neap tide than the spring tide. Their occurrence was related to subtidal shelf flows. The tidal and shelf flows had comparable magnitudes. We thus hypothesize that when the total flow meets critical conditions ISWs are generated locally over irregular seafloor. This hypothesis is supported by numerical experiments and validated by observations. Consequently, local generation of ISWs enhances both the intensity and complexity of internal wave field on the shelf, and thus the unpredictability of ISW occurrence.

A coherent status of summer monsoon phytoplankton communities (2017–2018) along the Western Indian continental shelf: Implications for fisheries

The western Indian continental shelf is characterized by contrasting biogeochemical features from south to north mostly governed by monsoon wind forcing. Here we present the first detailed study on the phytoplankton community (analyzed by marker pigments and microscopy) during the summer monsoon addressing the interannual variability (Aug 2017 and 2018) along the Western Indian Continental Shelf waters (8° N-21° N, at 200 m isobaths). A distinct interannual variability in monsoon impacted the hydrography and nutrient stoichiometry that was further cascaded to the phytoplankton community structure. The timing of the monsoon onset, wind speeds, and the strength of the alongshore wind component were the major factors that governed the interannual variability in the development and progression of the upwelling as well as phytoplankton bloom. The upwelling-dominated southwestern shelf was characterized by cold, nutrient-rich waters dominated by the marker pigment of diatoms, fucoxanthin, and microscopy also revealed the presence of large, chain-forming diatoms (Chaetoceros sp.; Dactyliosolen fragilissimus). In contrast, low nutrient warm waters in the northern shelf housed nanophytoplankton and picophytoplankton along with small diatoms (Thalassiosira sp.) and dinoflagellates (Gymnodinium sp.). Interestingly, in a few stations in the southern shelf, the surface waters were low saline that was intensified in 2018 compared to 2017 inhibiting upwelled water from reaching the surface. Consequently, due to low nutrient levels caused by reduced upwelling and low salinity, picoplanktonic cyanobacteria dominated replacing the larger diatoms that were found plenty in 2017. Likely, such a niche shift adversely impacted the planktivorous fish catch (Indian Oil Sardine) that was seen to be less in 2018 relative to 2017. Any further changes in monsoon variability and freshwater flow to this region may have direct consequences on the phytoplankton community as well as fisheries.

Sensitivity of fishery resources to climate change in the warm-temperate Southwest Atlantic Ocean

Climate change impacts on fishery resources have been widely reported worldwide. Nevertheless, a knowledge gap remains for the warm-temperate Southwest Atlantic Ocean—a global warming hotspot that sustains important industrial and small-scale fisheries. By combining a trait-based framework and long-term landing records, we assessed species’ sensitivity to climate change and potential changes in the distribution of important fishery resources (n = 28; i.e., bony fishes, chondrichthyans, crustaceans, and mollusks) in Southern Brazil, Uruguay, and the northern shelf of Argentina. Most species showed moderate or high sensitivity, with mollusks (e.g., sedentary bivalves and snails) being the group with the highest sensitivity, followed by chondrichthyans. Bony fishes showed low and moderate sensitivities, while crustacean sensitivities were species-specific. The stock and/or conservation status overall contributed the most to higher sensitivity. Between 1989 and 2019, species with low and moderate sensitivity dominated regional landings, regardless of the jurisdiction analyzed. A considerable fraction of these landings consisted of species scoring high or very high on an indicator for potential to change their current distribution. These results suggest that although the bulk of past landings were from relatively climate-resilient species, future catches and even entire benthic fisheries may be jeopardized because (1) some exploited species showed high or very high sensitivities and (2) the increase in the relative representation of landings in species whose distribution may change. This paper provides novel results and insights relevant for fisheries management from a region where the effects of climate change have been overlooked, and which lacks a coordinated governance system for climate-resilient fisheries.

Provenance and dispersal patterns of sediments on the continental shelf of northern South China Sea: Evidence from detrital zircon geochronology

The northern shelf of South China Sea is an important passageway for the transportation of sediments from the terrigenous source to the oceanic sink, but the provenance and dispersal patterns of sediments remain largely unclear. Here we report the results of zircon grain-size analysis and U-Pb geochronology to investigate the sediment provenance and illustrate the transport and dispersal patterns of sediments on the continental shelf of the northern South China Sea. The results show that detrital zircon U-Pb ages within sediments are characterized by a major peak at ca. 150 Ma, as well as three minor age populations at ca. 240 Ma, 400–500 Ma, and 900–1000 Ma. A detailed provenance study suggests that these sediments were primarily derived from both the Pearl River catchment and the drainage systems in Taiwan Island. Our study confirms that the transportation and dispersion of sediments were largely controlled by both topography and hydrodynamics of sea. The sediments in the inner continental shelf were transported from the Pearl River drainage system and subject to the Guangdong Coastal Current, whereas the sediments in the middle and outer continental shelf were markedly influenced by the South China Sea warm current. This study elucidates the transport and dispersal patterns of detrital sediments in the marginal sea by comprehensive analyses of detrital zircon grains.

Marine zoning for the Marine Plan Partnership (MaPP) in British Columbia, Canada

A zoning framework was developed for the Marine Plan Partnership for the North Pacific Coast (MaPP) in order to provide guidance for decisions regarding coastal and marine economic development, marine resource management, and marine protection or conservation across the MaPP region, the Northern Shelf Bioregion, British Columbia, Canada. The MaPP Zoning Framework was developed over an 18-month period at the beginning of the marine spatial planning (MSP) process with stakeholder consultation and incorporated lessons learned from other planning efforts in British Columbia and globally. The three main requirements for the Framework included that it was applicable and flexible for use across the MaPP regional boundary, which included four sub-regions that had diverse priorities and marine activities, that guiding principles for zoning would provide consistency for policy and other decisions within the MaPP regions, and that zone categories synergized with existing policy and legislation. A stakeholder advisory process was used to develop the Framework which resulted in three zone categories to achieve the goals of MaPP: Protection Management Zone (PMZ), Special Management Zone (SMZ), and General Management Zone (GMZ). Zone identification included numerous factors such as species and habitat diversity, cultural values, existing uses and activities, and priorities for sustainable economic development and conservation. The Framework was effectively used to zone 102,000 km2 of the MaPP region during the MSP process for more than 15 different sectors that were within the scope of the MaPP partners’ jurisdiction. Importantly, the Framework was successfully adapted across the four distinct MaPP sub-regions and consistently applied for an effective regional approach to decision making and management for both First Nations and provincial governments.

A gulf-wide synoptic isoscape of zooplankton isotope ratios reveals the importance of nitrogen fixation in supporting secondary production in the central Gulf of Mexico

A synoptic gulf-wide isoscape of carbon (δ13C) and nitrogen (δ15N) in the Gulf of Mexico based on mesozooplankton (335-1000 um) was used as a proxy for the isotopic baseline and for calculating regional contributions of dissolved inorganic nitrogen sources. Mesozooplankton were sampled at 0-200 m (depth permitting) during the XIXIMI-06 and GOMECC-3 cruises held during the summer of 2017. A striking latitudinal gradient was found in δ15N values of zooplankton, with the highest values (10.4 ± 1.2‰) found over the northern shelf, and lowest values in the central, oligotrophic gulf (1.9 ± 0.5‰). To estimate the fractional contribution of potential nitrogen sources, the gulf was divided into six regions based on the spatial distribution of surface Chl-a, SST from remote sensing products and likely region-specific source contributions. A literature survey of (δ13C and δ15N values of particulate organic matter was used to characterize region-specific endpoint isotope ratios for use in a Bayesian isotope mixing model. Regional differences in δ15N values and the results of mixing models indicated nitrogen fixation is most likely an important source (45-74% contribution) of new nitrogen in the oceanic regions of the Gulf, the Loop Current and the Yucatan Shelf. In the oligotrophic gulf, the potential input of relatively light nitrate that reflects remineralization of surface layer POM or the excretion of light nitrogen by heterotrophs was insufficient to explain the low δ15N values found in the central Gulf, although it could account for about 40% of the N supporting secondary production. The high nitrogen isotope ratios found in the northern shelf were attributed to denitrified N (60%) and the inflow of heavy nitrogen from the Mississippi-Atchafalaya river system. Our results support the potential importance of fixed nitrogen in the deep waters of the Gulf of Mexico during the summer, characteristic for its highly stratified surface waters.

Santos Basin continental shelf morphology, sedimentology, and slope sediment distribution

The ocean bottom morphology, depth, sediment grain size, sediment sorting, carbonate content, and water depth are used to compose seafloor maps as support for biological studies. Sediments are reworked by waves and currents and accumulate according to the hydrodynamic level on the continental shelf. In contrast, sediments are accumulated by pelagic settling, mass wasting, turbidity flows, and boundary currents on the slope. Sea level oscillations during the Quaternary also played an important role in modifying the shelf seabed's morphology and sedimentary mosaic composition. The work addresses these topics in the Santos Basin based on extensive bathymetric data, shallow seismic records, and stratified bottom sediment samples in water depths ranging from 25 to 2,400m, as part of The Santos Basin Regional Environmental Characterization Project (PCR-BS). The main objective is to provide broad background information on the sedimentology and morphology of Santos Basin, focusing on the continental shelf. The morphology, sediment supply, shelf orientation, and ocean climate imprint the Santos Basin's characteristics. The Northern shelf sector is the most dynamic because of the narrow shelf, steep gradient, and East-West shoreline orientation, providing conditions for storm waves to approach and mobilize sediment in the ocean bottom shallow than 50 m water depth. The Southern sector of the shelf is much broader than the Northern sector; it displays a gentler gradient, and its orientation is Northeast-Southwest; therefore, less subject to storm waves than the Northern sector.

Investigation of various pipe materials for riser operation in the arctic seas

А riser, which is an offshore water separation column is the main difference between offshore drilling and onshore drilling. The idea of the research is to calculate the stressed-deformed state of a riser made of various materials to identify technological advantages during drilling on the shelf and at sea in the Arctic. The article is the result of research conducted in the Mathematica application program to determine the operating stresses that depend on the drilling process conditions and the external environment. Modern drilling technologies are designed to increase the capacity of the equipment or to use alternative materials. Given the pace of development of the fields of the Northern Shelf of Russia, there is a need to explore the use of alternative materials for such marine equipment as risers.