Category: Poster

Recent rapid sea-ice reduction in the Arctic Ocean (AO) has been well documented in model simulations, observations, and reconstructions. The decline in Arctic sea ice in recent decades has been attributed, in large part, to increasing greenhouse warming and we are expected to observe an ice-free summer in upcoming decades. As a result of the above trends in observed Arctic sea ice, it is important to understand the consequences of Arctic sea ice loss for both local and global climate patterns and marine ecosystems. To understand these consequences, we present a review of recent studies that investigate the implications of Arctic sea ice loss. We will in particular focus on sea ice decline in the Barents Sea (20-60°E, 67.5-85°N). Changes to Atlantic Water inflow in this region play a significant role in determining sea ice cover. Through the case study on the Barents Sea, we conclude that the main consequences of Arctic sea ice loss in recent decades include; disturbance of global weather patterns, a threat to coastal communities, and extreme temperatures. We also demonstrate how a decline in sea ice in the AO, will drive further Arctic warming and sea ice loss due to Arctic Amplification. The above consequences provide a rationale for continued monitoring of Arctic sea ice.

The Atlantic Meridional Overturning Circulation (AMOC) is projected to experience a slowdown due to anthropogenic global warming. Concurrently, the Arctic Ocean is undergoing rapid transformations, including retreating sea ice extent, changing freshwater inputs from rivers and melting ice and increased Atlantic Water (AW) heat transport and air-sea heat fluxes. Following the realization that not only the Nordic Seas, but also the Arctic Ocean is a major component in sustaining the AMOC, the Arctic Ocean has emerged as a region of particular interest for further research. In the Arctic Ocean, the transformation of AW yields two key products, related to distinct overturning circulation branches: dense overflow waters, contributing to the thermal overturning branch, and Polar Waters (PW) created by mixing with freshwater from sources like rivers and melting ice, forming the estuarine circulation branch. Here we will discuss an outlook for the Arctic Ocean overturning in a future climate, as well as some of the processes involved in potentially counterbalancing AMOC decline. For instance, recent research contrastingly highlights the potential for a northward shift of deep convection areas, strengthening Arctic overturning, and the potential for the collapse of one of its overturning cells.

The general surface circulation of the Nordic Seas consists of poleward flowing relatively warm waters from the Atlantic and a return flow along the East Greenland Current with colder and fresher waters, along with transformed Atlantic waters sub-surface. The mid-depth circulation of the Nordic Seas, particularly the exchange between the various basins, however, has not been well studied, but is important for understanding the main pathways between dense water formation regions towards the overflows of the Greenland Scotland Ridge. The transformation of the water to denser and colder waters is important for dense water overflowing towards the North Atlantic and supplying the lower limb of the AMOC. Here we use Argo floats drifting at intermediate depths (1000 – 1500 m) to provide an overview of this mid-depth circulation. We found the highest velocities along the boundaries and in the Norwegian Sea along steep topography, while the velocities in the interior basins are lower. Floats generally remain within the basin they were deployed in unless they are entrained into the boundary current. This occurs primarily when the interior gyre circulation is close to the boundary, or where steep topography can cause instabilities. The exchanges across submarine ridges show certain preferred inter-basin pathways, except for the crossings between the Greenland and Lofoten Seas. This circulation shows similar features to the surface boundary current, but interior pathways are distinctly different and reveal the main pathways connecting the basins.

Warm water from the Atlantic is flowing into the Arctic through the Fram strait, after following the Norwegian coast. After a full circulation in the Arctic Sea, it exits through the Fram strait again, only now as a denser water mass in the East Greenland Current (EGC). The Atlantic Current that circumnavigates in the Arctic is an extension of the Atlantic Water Boundary Current (AWBC) and flows eastwards along the northern continental slope of Eurasia and North America. During this circulation the AWBC is gradually being modified to a denser water mass. During its circulation the AWBC interacts with freshwater input from continental rivers, the sea-ice cover, different types of bathymetries, the atmosphere and other different water masses in the Arctic. Over the most recent decades a retreating sea ice cover has increased the amount of interaction between AWBC and the atmosphere, implying an increase in water modification due to heat loss to the atmosphere. This poster will elaborate the modification throughout.

The Antarctic Slope Current (ASC) circumnavigates the Antarctic continent following the continental slope, separating the waters on the continental shelf from the deeper offshore Southern Ocean and regulates the flow towards the Antarctic coastline. We can classify the current’s frontal structure in 3 ranges: warm shelf, fresh shelf and dense shelf. It is difficult to reveal its spatial and sub-annual variability, as direct velocity measurements are sparse. Spatial variability of the ASC has also been characterized as three flow regimes: the surface-intensified ASC, the bottom-intensified ASC, and the reversed ASC. The surface-intensified ASC regime is stronger in the winter months. Seasonality of the winds may be the relevant driver for the seasonality along stretches of the coastline with a surface-intensified ASC. The reversed ASC has an inverted seasonality, meaning it is weaker in the winter months. The surface-intensified ASC occurs at sections of the continental slope with a fresh shelf, the bottom-intensified ASC occurs at dense shelves, and the reversed ASC occurs at warm shelves. Seasonality of the ASC is influenced not only by the mechanical forcing provided by the winds and sea ice at the ocean surface, but also by a geostrophic adjustment to changes in the cross-slope density gradient via freshwater input from basal melting and via surface water mass transformation.

The East Greenland Current (EGC) transports fresh and cold Polar Water (PW) southwards from the central Arctic Ocean. Observations of strength and properties of the EGC have been monitored through moored instruments in Fram Strait since 1997. Freshwater transport since 2015 has decreased, with an exception for 2017. The general decrease is caused by a velocity reduction of the EGC and PW. Results points to an “Atlantification” of the western Fram Strait section. Mechanisms controlling the export of freshwater from the EGC, both in liquid and solid forms, are explored using an idealized numerical model and scaling theory. Climate models predict an increase of offshore winds and decrease in Arctic export of sea-ice for the coming future. This leads to a decrease in offshore sea-ice transport. Uncertainties occur for onshore freshwater transport, as it may both increase or decrease depending on the changing effects of Ekman transport and offshore eddy fluxes.