Alfred Wegener Institute for Polar and Marine Research
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Structure and Seasonal Variability of the Arctic Boundary Current North of Severnaya Zemlya
Get PDFWe assessed the spatial and temporal variability of the Arctic Boundary Current (ABC) using seven oceanographic moorings, deployed across the continental slope north of Severnaya Zemlya in 2015–2018. Transports and individual water masses were quantified based on temperature and salinity recorders and current profilers. Our results were compared with observations from the northeast Svalbard and the central Laptev Sea continental slopes to evaluate the hydrographic transformation along the ABC pathway. The highest velocities (>0.30 m s−1) of the ABC occurred at the upper continental slope and decreased offshore to below 0.03 m s−1 in the deep basin. The ABC showed seasonal variability with velocities two times higher in winter than in summer. Compared to upstream conditions in Svalbard, water mass distribution changed significantly within 20 km of the shelf edge due to mixing with- and intrusion of shelf waters. The ABC transported 4.15 ± 0.3 Sv in the depth range 50–1,000 m, where 0.88 ± 0.1, 1.5 ± 0.2, 0.61 ± 0.1 and 1.0 ± 0.15 Sv corresponded to Atlantic Water (AW), Dense Atlantic Water (DAW), Barents Sea Branch Water (BSBW) and Transformed Atlantic Water (TAW). 62–70% of transport was constrained to within 30–40 km of the shelf edge, and beyond 84 km, transport increases were estimated to be 0.54 Sv. Seasonality of TAW derived from local shelf-processes and advection of seasonal-variable Fram Strait waters, while BSBW transport variability was dominated by temperature changes with maximum transport coinciding with minimum temperatures. Further Barents Sea warming will likely reduce TAW and BSBW transport leading to warmer conditions along the ABC pathway
Nunataryuk field campaigns: understanding the origin and fate of terrestrial organic matter in the coastal waters of the Mackenzie Delta region
Get PDFClimate warming and related drivers of soil thermal change in the Arctic are expected to modify the distribution and dynamics of carbon contained in perennially frozen grounds. Thawing of permafrost in the Mackenzie River watershed of northwestern Canada, coupled with increases in river discharge and coastal erosion, triggers the release of terrestrial organic matter (OMt) from the largest Arctic drainage basin in North America into the Arctic Ocean. While this process is ongoing and its rate is accelerating, the fate of the newly mobilized organic matter as it transits from the watershed through the delta and into the marine system remains poorly understood. In the framework of the European Horizon 2020 Nunataryuk programme, and as part of the Work Package 4 (WP4) Coastal Waters theme, four field expeditions were conducted in the Mackenzie Delta region and southern Beaufort Sea from April to September 2019. The temporal sampling design allowed the survey of ambient conditions in the coastal waters under full ice cover prior to the spring freshet, during ice breakup in summer, and anterior to the freeze-up period in fall. To capture the fluvial-marine transition zone, and with distinct challenges related to shallow waters and changing seasonal and meteorological conditions, the field sampling was conducted in close partnership with members of the communities of Aklavik, Inuvik and Tuktoyaktuk, using several platforms, namely helicopters, snowmobiles, and small boats. Water column profiles of physical and optical variables were measured in situ, while surface water, groundwater, and sediment samples were collected and preserved for the determination of the composition and sources of OMt, including particulate and dissolved organic carbon (POC and DOC), and colored dissolved organic matter (CDOM), as well as a suite of physical, chemical, and biological variables. Here we present an overview of the standardized datasets, including hydrographic profiles, remote sensing reflectance, temperature and salinity, particle absorption, nutrients, dissolved organic carbon, particulate organic carbon, particulate organic nitrogen, CDOM absorption, fluorescent dissolved organic matter intensity, suspended particulate matter, total particulate carbon, total particulate nitrogen, stable water isotopes, radon in water, bacterial abundance, and a string of phytoplankton pigments including total chlorophyll. Datasets and related metadata can be found in (10.1594/PANGAEA.937587)
Spatial distribution of amphipod assemblages in Marine Protected Areas of the German Bight (North Sea)
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Uniquely low stable iron isotopic signatures in deep marine sediments caused by Rayleigh distillation
Get PDFDissimilatory iron reduction (DIR) is suggested to be one of the earliest forms of microbial respiration. It plays an important role in the biogeochemical cycling of iron in modern and ancient sediments. Since microbial iron cycling is typically accompanied by iron isotope fractionation, stable iron isotopes are used as tracer for biological activity. Here we present iron isotope data for dissolved and sequentially extracted sedimentary iron pools from deep and hot subseafloor sediments retrieved in the Nankai Trough off Japan. Dissolved iron (Fe(II)aq) is isotopically light throughout the ferruginous sediment interval but some samples have exceptionally light isotope values. Such light values have never been reported in natural marine environments and cannot be solely attributed to DIR. We show that the light isotope values are best explained by a Rayleigh distillation model where Fe(II)aq is continuously removed from the pore water by adsorption onto iron (oxyhydr)oxide surfaces. While the microbially mediated Fe(II)aq release has ceased due to an increase in temperature beyond the threshold of mesophilic microorganisms, the abiotic adsorptive Fe(II)aq removal continued, leading to uniquely light isotope values. These findings have important implications for the interpretation of dissolved iron isotope data especially in deep subseafloor sediments
Three major mesoplanktonic communities resolved by in situ imaging in the upper 500 m of the global ocean
Get PDFAim: The distribution of mesoplankton communities has been poorly studied at global scale, especially from in situ instruments. This study aims to (1) describe the global distribution of mesoplankton communities in relation to their environment and (2) as-sess the ability of various environmental- based ocean regionalizations to explain the distribution of these communities.
Location: Global ocean, 0–500 m depth.
Time Period: 2008–2019.
Major Taxa Studied: Twenty-eight groups of large mesoplanktonic and macroplank-tonic organisms, covering Metazoa, Rhizaria and Cyanobacteria.
Methods: From a global data set of 2500 vertical profiles making use of the Underwater Vision Profiler 5 (UVP5), an in situ imaging instrument, we studied the global distribu-tion of large (>600 μm) mesoplanktonic organisms. Among the 6.8 million imaged ob-jects, 330,000 were large zooplanktonic organisms and phytoplankton colonies, the rest consisting of marine snow particles. Multivariate ordination (PCA) and clustering were used to describe patterns in community composition, while comparison with existing regionalizations was performed with regression methods (RDA).
Results: Within the observed size range, epipelagic plankton communities were Trichodesmium- enriched in the intertropical Atlantic, Copepoda- enriched at high latitudes and in upwelling areas, and Rhizaria-enriched in oligotrophic areas. In the mesopelagic layer, Copepoda-enriched communities were also found at high lati-tudes and in the Atlantic Ocean, while Rhizaria-enriched communities prevailed in the Peruvian upwelling system and a few mixed communities were found elsewhere. The comparison between the distribution of these communities and a set of existing regionalizations of the ocean suggested that the structure of plankton communities described above is mostly driven by basin- level environmental conditions.
Main Conclusions: In both layers, three types of plankton communities emerged and seemed to be mostly driven by regional environmental conditions. This work sheds light on the role not only of metazoans, but also of unexpected large protists and cy-anobacteria in structuring large mesoplankton communities
A Review of Arctic–Subarctic Ocean Linkages: Past Changes, Mechanisms, and Future Projections
Get PDFArctic Ocean gateway fluxes play a crucial role in linking the Arctic with the global ocean and affecting climate and marine ecosystems. We reviewed past studies on Arctic–Subarctic ocean linkages and examined their changes and driving mechanisms. Our review highlights that radical changes occurred in the inflows and outflows of the Arctic Ocean during the 2010s. Specifically, the Pacific inflow temperature in the Bering Strait and Atlantic inflow temperature in the Fram Strait hit record highs, while the Pacific inflow salinity in the Bering Strait and Arctic outflow salinity in the Davis and Fram straits hit record lows. Both the ocean heat convergence from lower latitudes to the Arctic and the hydrological cycle connecting the Arctic with Subarctic seas were stronger in 2000–2020 than in 1980–2000. CMIP6 models project a continuing increase in poleward ocean heat convergence in the 21st century, mainly due to warming of inflow waters. They also predict an increase in freshwater input to the Arctic Ocean, with the largest increase in freshwater export expected to occur in the Fram Strait due to both increased ocean volume export and decreased salinity. Fram Strait sea ice volume export hit a record low in the 2010s and is projected to continue to decrease along with Arctic sea ice decline. We quantitatively attribute the variability of the volume, heat, and freshwater transports in the Arctic gateways to forcing within and outside the Arctic based on dedicated numerical simulations and emphasize the importance of both origins in driving the variability.</jats:p
Potential of calcein staining as growth monitoring marker in Ostrea edulis
Get PDFGrowth is an important biological trait and monitoring metric for the assessment of the success and progress of restoration projects with the European oyster (Ostrea edulis). However, sampling time and frequency are often limited, as well as the ability to survey individual growth. Chemical dyes, such as calcein, can be used to create incremental markings for measuring growth in shell cross-sections, especially in bivalves. However, potential negative effects and limits for successful staining have not been assessed for O. edulis, yet. In this study, three different calcein concentrations (100-mg l-1, 150-mg l-1, 200-mg l-1) with three different immersion times (6-h, 12-h, 24-h) were tested for potential negative effects, the best incremental marking result and their potential to be used in growth measurements. Furthermore, the deposition of an annual growth line was investigated. Results showed that calcein is a reliable in situ fluorescence marker that produced sufficient growth lines in the cross-section of O. edulis. At a concentration of 100-mg l-1 or higher and immersion times of 6-h or more, no negative effects on growth and survival were observed after five months. Applications include the possibility for long-term, individual growth data for a large number of oysters for restoration monitoring as well as the option of marking restored oysters from aquaculture production to distinguish them from existing wild stock populations or natural offspring
On their way to the north: larval performance of Hemigrapsus sanguineus invasive to the European coast—a comparison with the native European population of Carcinus maenas
Get PDFThe Asian shore crab Hemigrapsus sanguineus has become invasive in North Europe and it co-occurs and competes with the native European shore crab Carcinus maenas. Both species develop through a feeding and dispersive larval phase characterised by several zoeal and a settling megalopa stage. Larvae of marine crabs are vulnerable to food limitation and warming has the potential to exacerbate the negative effects of food limitation on survival and growth. We quantified the combined effects of temperature and food limitation on larval performance (survival and growth) of H. sanguineus and we compared our results with those reported on performance of C. maenas larvae, under the same experimental design and methodology. Larvae from four females of H. sanguineus collected on Helgoland (North Sea) were experimentally reared from hatching to megalopa, at four temperatures (range 15–24 °C) and two food conditions (permanent vs. daily limited access to food). Larval survival of H. sanguineus was low at 15 °C and increased with temperature, in contrast to the high survival reported for C. maenas larvae in the range 15–24 °C. Food limitation reduced survival and body mass of H. sanguineus larvae at all temperatures, but without evidence of the exacerbating effect caused by high temperatures and reported for C. maenas. By contrast, high temperature (24 °C) mitigated the negative effect of food limitation on body mass on H. sanguineus larvae. Advantages of H. sanguineus over C. maenas appear especially under the increased temperatures expected from climate change
