Structure, variability, and dynamics of the West Greenland Boundary Current System

The ventilation of intermediate waters in the Labrador Sea has important implications for the strength of the Atlantic Meridional Overturning Circulation. Boundary current-interior interactions regulate the exchange of properties between the slope and the basin, which in turn regulates the magnitude of interior convection and the export of ventilated waters from the subpolar gyre. This thesis characterizes theWest Greenland Boundary Current System near Cape Farewell across a range of spatio-temporal scales. The boundary current system is composed of three velocity cores: (1) the West Greenland Coastal Current (WGCC), transporting Greenland and Arctic meltwaters on the shelf; (2) the West Greenland Current (WGC), which advects warm, saline Atlantic-origin water at depth, meltwaters at the surface, and newly-ventilated Labrador Sea Water (LSW); and (3) the Deep Western Boundary Current, which carries dense overflow waters ventilated in the Nordic Seas. The seasonal presence of the LSW and Atlantic-origin water are dictated by air-sea buoyancy forcing, while the seasonality of the WGCC is governed by remote wind forcing and the propagation of coastally trapped waves from East Greenland. Using mooring data and hydrographic surveys, we demonstrate mid-depth intensified cyclones generated at Denmark Strait are found offshore of the WGC and enhance the overflow water transport at synoptic timescales. Using mooring, hydrographic, and satellite data, we demonstrate that the WGC undergoes extensive meandering due to baroclinic instability that is enhanced in winter due to LSW formation adjacent to the current. This leads to the production of small-scale, anticyclonic eddies that can account for the entirety of wintertime heat loss within the Labrador Sea. The meanders are shown to trigger the formation of Irminger Rings downstream. Using mooring, hydrographic, atmospheric, and Lagrangian data, and a mixing model, we find that strong atmospheric storms known as forward tip jets cause upwelling at the shelfbreak that triggers offshore export of freshwater. This freshwater flux can explain the observed lack of ventilation in the eastern Labrador Sea. Together, this thesis documents previously unobserved interannual, seasonal, and synoptic-scale variability and dynamics within the West Greenland boundary current system that must be accounted for in future modeling.

A new record of the brassy chub, Kyphosus vaigiensis (Actinopterygii: Perciformes: Kyphosidae), from the Mediterranean Sea

One individual of the brassy chub, Kyphosus vaigiensis (Quoy et Gaimard, 1825) (41.5 cm TL, 1.27 kg TW), was caught off Annaba, on the eastern coasts of Algeria in December 2013. This circumtropical fish is found for the first time on the south-western Mediterranean coasts. The chronology of its records in the Mediterranean supports the hypothesis of its Atlantic origin.

Polychaetes (Annelida: Polychaeta) of the Kara Sea

As a result of processing materials from the expeditions of the Saint-Petersburg State University in 2012–2013 and the Transarctic expedition of 2019, 131 polychaete taxa were recorded, of which 124 were identified to species. On the basis of data from previous and recent collections, the general list of polychaetes in the Kara Sea was updated; it includes 209 species belonging to 98 genera, 37 families, and 15 orders. The following species are reported for the first time from the sea: Abyssoninoe hibernica (McIntosh, 1903), Ampharete falcata Eliason, 1955, Brada rugosa Hansen, 1882, Microclymene acirrata Arwidsson, 1906; Nephtys pente Rainer, 1984; Ophelina abranchiata Stop-Bowitz, 1948, Scolelepis burkovskii Sikorski, 1994, and Travisia forbesii Johnson, 1840. Polychaetes were found at all stations; the number of species per station ranged from 1 to 28. Shannon’s indices (H'SpA and H'spB) showed that at most stations the diversity of species was high and resistance to stress (DE') was quite satisfactory. Only in a few cases some tension existed in the ecological situation, estimated by the index of difference in evenness and this applies, to an overwhelming degree, to the shallow water stations in the area of the outlet from the Ob and Yenisei bays. New data show a more pronounced Arctic character of the Kara Sea fauna in comparison with the polychaete fauna of neighboring seas. The influence of the Pacific and Atlantic oceans both on the polychaete fauna of the Kara Sea and on the polychaete fauna of the neighboring seas is noticeable and natural, which is confirmed by changes in the proportion of species of Pacific and Atlantic origin. The trophic structure of polychaetes is represented by four main groups; the distribution of trophic groups is closely related to environmental conditions.

Drivers of sea ice decline in the Fram Strait and north of Svalbard

<p>The Arctic Ocean is undergoing rapid change. Satellite observations indicate significant negative Arctic sea ice extent trends in all months and substantial reduction of winter sea ice in the Atlantic sector. One of the possible reasons can be sought in the observed warming of Atlantic water, carried through Fram Strait into the Arctic Ocean. Fram Strait, as well as the region north of Svalbard, play a key role in controlling the amount of oceanic heat supplied to the Arctic Ocean and are the place of dynamic interaction between the ocean and sea ice. Shrinking sea ice cover in the southern part of Nansen Basin (north of Svalbard) and shifting the ice edge in Fram Strait are driven by the interplay between increased advection of oceanic heat in the Atlantic origin water and changes in the local atmospheric conditions.</p><p>Processes related to the loss of sea ice and the upward transport of heat from the layers of the Arctic Ocean occupied by the Atlantic water are still not fully explored, but higher than average temperature of Atlantic inflow in the Nordic Seas influence the upper ocean stratification and ice cover in the Arctic Ocean, in particular in the north of Svalbard area. The regional sea ice cover decline is statistically signifcant in all months, but the largest changes in the Nansen Basin are observed in winter season. The winter sea ice loss north of Svalbard is most pronounced above the core of the inflow warm Atlantic water. The basis for this hypothesis of the research is that continuously shrinking sea ice cover in the region north of Svalbard and withdrawal of the sea ice cover towards the northeast are driven by the interplay between increased oceanic heat in the Atlantic origin water and changes in the local atmospheric conditions, that can result in the increased ocean-air-sea ice exchange in winter seasons. In the current study we describe seasonal, interannual and decadal variability of concentration, drift, and thickness of sea ice in two regions, the north of Svalbard and central part of the Fram Strait, based on the satellite observations. To analyze the observed changes in the sea ice cover in relation to Atlantic water variability and atmospheric forcing we employ hydrographic data from the repeated CTD sections and new atmospheric reanalysis from ERA5. Atlantic water variability is described based on the set of summer synoptic sections across the Fram Strait branch of the Atlantic inflow that have been occupied annually since 1996 under the long-term observational program AREX of the Institute of Oceanology PAS. To elucidate driving mechanisms of the sea ice cover changes observed in different seasons in Fram Strait and north of Svalbard we analyze changes in the temperature, heat content and transport of the Atlantic water and describe their potential links to variable atmospheric forcing, including air temperature, air-ocean fluxes, and changes in wind pattern and wind stress.</p>

A changing Arctic Ocean: How measured and modeled 129I distributions indicate fundamental shifts in circulation between 1994 and 2015

<p><sup>129</sup>I measurements on samples collected during GEOTRACES oceanographic missions in the Arctic Ocean in 2015 have provided the first detailed, synoptic <sup>129</sup>I sections across the Eurasian, Canada and Makarov Basins. <sup>129</sup>I is discharged from European nuclear fuel reprocessing plants since several decades and is carried north into the Arctic Ocean with waters of Atlantic origin. Here the measurements of its passage can be used to identify the ocean circulation at different depth horizons. Elevated <sup>129</sup>I levels measured over the Lomonosov and Alpha-Mendeleyev Ridges in 2015 were associated with tracer labeled, Atlantic-origin water bathymetrically steered by the ridge systems through the central Arctic while lower <sup>129</sup>I levels were evident in the more poorly ventilated basin interiors. <sup>129</sup>I levels of 200-400 x 10<sup>7</sup> at/l measured in intermediate waters had increased by a factor of 10 compared to results from the same locations in 1994-1996 owing to the arrival of a strong increase in the discharges from La Hague, that occurred during the 1990s. Comparisons of the patterns of <sup>129</sup>I between the mid-1990s and 2015 delineate large scale circulation changes that occurred during the shift from a positive Arctic Oscillation and a cyclonic circulation regime in the mid-1990s to anticyclonic circulation in 2015. These are characterized by a broadened Beaufort Gyre in the upper ocean, a weakened boundary current and partial AW flow reversal in the southern Canada Basin at mid-depth. Tracer <sup>129</sup>I simulations using the coupled ocean-sea ice model NAOSIM agree with both, the historical <sup>129</sup>I results and recent GEOTRACES data sets, thereby lending context and credibility to the interpretation of large-scale changes in Arctic circulation and their relationship to shifts in climate indices revealed by the tracer <sup>129</sup>I distributions. We will present measurements and simulation results of <sup>129</sup>I for the 1990s and 2015 and put them into the context of ocean circulation responses to changing atmospheric forcing regimes.</p>

Floating marine macro-litter distribution in the Russian Arctic Seas in relation to oceanographic characteristics

<p>The main objectives of this work was the acquisition of new data on floating marine macro litter (FMML) and natural floating objects in the Arctic seas, an initial assessment of the level of pollution by FMML and an analysis of potential sources. The results of this study present the first data on FMML distribution in Russian Arctic shelf seas in relation to oceanographic conditions (i.e. position of water masses of different origin as described by temperature, salinity, dissolved oxygen and pH). The main finding of this study is that FMML was found only in the water of Atlantic origin, inflowing from the Barents Sea, where FMML average density on the observed transects was 0.92 items/ km2. Eastern parts of the study, Kara Sea, Laptev Sea and East Siberian Sea were practically free from FMML. The input from rivers appears to be negligible, at least in autumn.</p>

Microplastics distribution in the Eurasian Arctic is affected by Atlantic waters and Siberian rivers

Plastic pollution is globally recognised as a threat to marine ecosystems, habitats, and wildlife, and it has now reached remote locations such as the Arctic Ocean. Nevertheless, the distribution of microplastics in the Eurasian Arctic is particularly underreported. Here we present analyses of 60 subsurface pump water samples and 48 surface neuston net samples from the Eurasian Arctic with the goal to quantify and classify microplastics in relation to oceanographic conditions. In our study area, we found on average 0.004 items of microplastics per m3 in the surface samples, and 0.8 items per m3 in the subsurface samples. Microplastic characteristics differ significantly between Atlantic surface water, Polar surface water and discharge plumes of the Great Siberian Rivers, allowing identification of two sources of microplastic pollution (p < 0.05 for surface area, morphology, and polymer types). The highest weight concentration of microplastics was observed within surface waters of Atlantic origin. Siberian river discharge was identified as the second largest source. We conclude that these water masses govern the distribution of microplastics in the Eurasian Arctic. The microplastics properties (i.e. abundance, polymer type, size, weight concentrations) can be used for identification of the water masses.

Ryder Glacier in northwest Greenland is shielded from warm Atlantic water by a bathymetric sill

The processes controlling advance and retreat of outlet glaciers in fjords draining the Greenland Ice Sheet remain poorly known, undermining assessments of their dynamics and associated sea-level rise in a warming climate. Mass loss of the Greenland Ice Sheet has increased six-fold over the last four decades, with discharge and melt from outlet glaciers comprising key components of this loss. Here we acquired oceanographic data and multibeam bathymetry in the previously uncharted Sherard Osborn Fjord in northwest Greenland where Ryder Glacier drains into the Arctic Ocean. Our data show that warmer subsurface water of Atlantic origin enters the fjord, but Ryder Glacier’s floating tongue at its present location is partly protected from the inflow by a bathymetric sill located in the innermost fjord. This reduces under-ice melting of the glacier, providing insight into Ryder Glacier’s dynamics and its vulnerability to inflow of Atlantic warmer water.

The mesoscale eddy field in the Lofoten Basin from high-resolution Lagrangian simulations

Warm Atlantic-origin waters are modified in the Lofoten Basin in the Nordic Seas on their way toward the Arctic. An energetic eddy field redistributes these waters in the basin. Retained for extended periods, the warm waters result in large surface heat losses to the atmosphere and an impact on fisheries and regional climate. Here, we describe the eddy field in the Lofoten Basin by analysing Lagrangian simulations forced by a high-resolution numerical model. We obtain trajectories of particles seeded at three levels: near the surface, at 200 m and 500 m depth, using 2D and 3D velocity fields. About 200,000 particle trajectories are analyzed from each level and each simulation. Using multivariate wavelet ridge analysis, we identify coherent cyclonic and anticyclonic vortices in the trajectories and describe their characteristics. We then compare the evolution of water properties inside cyclones and anticyclones as well as in the ambient flow outside vortices. As measured from Lagrangian particles, anticyclones have longer lifetimes than cyclones (16–24 days compared to 13–19 days), larger radius (20–22 km compared to 17–19 km) and a more circular shape (ellipse linearity of 0.45–0.50 compared to 0.51–0.57). The angular frequencies for cyclones and anticyclones have similar magnitudes (absolute values of about 0.05f). The anticyclones are characterized by warm temperature anomalies whereas cyclones are colder than the background state. Along their path, water parcels in anticyclones cool at a rate of 0.02–0.04 °C/day while those in cyclones warm at a rate of 0.01–0.02 °C/day. Water parcels experience a net downward motion in anticyclones and upward motion in cyclones, often found to be related to changes in temperature and density. The along-path changes of temperature, density and depth are smaller for particles in the ambient flow. An analysis of the net temperature and vorticity fluxes into the Lofoten Basin shows that while vortices contribute significantly to the heat and vorticity budgets, they only cover a small fraction of the domain area (about 6 %). The ambient flow, including filaments and other non-coherent variability undetected by the ridge analysis, hence plays a major role in closing the budgets of the basin.