Circulation in the Arctic Ocean and the Nordic Seas

The Norwegian Atlantic Current is the extension of the North Atlantic Current in the Nordic Seas and transports warm waters from the mid-latitudes to the Arctic Ocean. The Atlantic-derived water propagates in a boundary current through the entire Arctic Mediterranean. Along its pathway, Atlantic water transitions into several prominent branches, and releases heat to the surrounding water, ice cover and atmosphere. To capture any changes in the warm northward flow, we monitor the Atlantic Water in the West Spitsbergen Current in Fram Strait by use of an oceanographic mooring array since 1997.

Surface waters are densified through cooling and brine release during ice formation, and subsequently sink to depth. These sinking waters form a part of the dense overflow waters spilling over the Denmark Scotland Ridge, which closes the cyclonic circulation through the Arctic Mediterranean.

A particular feature of the Arctic Ocean is the enormous freshwater surplus. The upper Arctic Ocean receives freshwater from the Pacific inflow, through runoff from large rivers and through the distilling process of sea ice formation and melting. Nearly 11% of the global river runoff enters the Arctic, with the majority discharged to the Siberian shelves. This leads to a strongly stratified upper ocean, separating the warm and saline Atlantic waters from the sea ice and the atmosphere. The main wind-driven ice and surface circulation features are the anti-cyclonic (freshwater storing) Beaufort Gyre, and the Transpolar Drift, which drives the freshwater towards Greenland and Fram Strait from where it is eventually exported to the subpolar North Atlantic.

The Arctic freshwater inventory has substantially increased over the last decades. This accumulation might be part of a multi-decadal oscillation, which is linked to the subpolar North Atlantic, where the freshwater can influence deep-water formation. To understand the underlying mechanisms, we conduct long-term observations to document the freshwater changes and analyze the observations in close cooperation with numerical modeling efforts. The freshwater (solid and liquid) is eventually exported to the sub-polar North Atlantic. One part of the export occurs with the East Greenland Current, which episodically leaks freshwater into the interior Greenland and Icelandic seas, where it may impact deep water formation and hence the formation of overflow waters. We investigate freshwater leakage mechanisms from the East Greenland Current with a long-mission autonomous glider program.  

Greenland’s ice sheet loses mass at an alarming rate, with yet unknown consequences for the meridional overturning circulation and the regional sea level distribution. Advection of warming North Atlantic water to Greenland’s marine outlet glaciers may enhance glacial melt and likely contributes to a destabilization of the Greenland ice streams. We observed Atlantic water warming in Fram Strait and this water is likely to affect the (presently) stable North East Greenland ice stream (NEGIS), one of the largest Greenland ice streams. We investigate the mechanisms that transfer the warm Atlantic water from the return flow in Fram Strait towards the 79°N glacier which is the main outlet glacier onto the shelf east of Greenland.

Shallow shelf seas occupy ~40% of the Arctic Ocean’s area. The shelves’ current systems convey the freshwater from the sources at the rim to the central Arctic and the Transpolar Drift. In addition, upwelling mechanisms persist that transport the intermediate warm Atlantic-derived waters from along the continental slopes to the bottom waters of the shallow shelves, some of which contain submarine permafrost and gas hydrates. Offshore-directed winds in winter frequently open leads and polynyas in the ice cover, i.e. local “cold spots”, characterized by strong oceanic heat loss and large sea ice formation rates. Polynyas produce those cold and dense shelf waters, that spread beyond the shelf edge and ventilate the intermediate and deep layers of the Arctic Ocean, thereby forming the Arctic contribution to the dense waters of the Greenland-Shetland-Overflow. To study the Arctic shelf processes, exemplified in the Laptev Sea, we use oceanographic moorings and high-resolution hydrographic observations in co-operation with Russian partners.