Tracking the Atlantic Waters in the Arctic Ocean

Rebecca Woodgate

Below about 200m , the main circulation of the Arctic Ocean is believed to be a pan-Arctic boundary current, entering the Arctic through the Fram Strait and the Barents Sea, and following the topography in an anti-clockwise manner around the various Arctic Basins.  In many ways this is a climate hand-shake of the Arctic with the rest of the world, since these waters are modified in the Arctic and then return to the Atlantic Ocean exiting the Arctic via Fram Strait.  It is somewhat humbling to appreciate how little we know about this circulation.  It has been inferred from mostly summer measurements of temperature, salinity, and some chemical tracers. 

A few-year round  installations (moorings) have attempted to quantify the nature of this current (e.g. Lomonosov moorings and the NABOS program), but these sites give us only brief and local glimpses of a system which is the size of the continental USA.  Modeling studies can suggest possible schemes and properties for this circulation (e.g., AOMP – Arctic Ocean Model Intercomparison Project), but there is not enough observational data to confirm these results, or to resolve discrepancies between models.  The current moves slowly in the Arctic – a few cm/s at best – but there are occasional more energetic features, eddies, which may be almost 40 cm/s (almost 1 knot) extending kms in the vertical.   In addition, it appears that molecular scale processes may (currently) have a basin-wide manifestation.  Double diffusion (motion arising from changes in density driven by the difference in speed of diffusion of heat and salt) appears to drive interleaving layers between the boundary current and the interior of the Arctic.  To understand this system will require a combination of observational, modeling and theoretical techniques.  

Here are some links for efforts in this direction:
- observationally motivated project, combining modern analysis techniques with historic observational data in the Western Arctic
- year-round measurements of the Arctic Ocean Boundary Current in the eastern Arctic
- the Nansen and Amundsen Basins Observational System project

Monitoring of oceanic fluxes across Fram Strait

U. Schauer,  W.-J. von Appen, B. Rabe, A. Beszczynska-Möller (formerly), E. Fahrbach (formerly) Alfred Wegener Institute (AWI), Helmholtz Centre for Polar and Marine Research, Bremerhaven, Germany
L. de Steur, P.A. Dodd, E. Hansen (formerly)Norwegian Polar Institute (NPI), Tromsø, Norway

The Fram Strait is only deep ocean connection between the Arctic Ocean and the Nordic Seas. It is about 600km wide of which approximately half is the 200m deep East Greenland shelf and the other half is up to 2500m deep. Deep water exchanges between the two basins pass through the Fram Strait. The inflow of warm and saline Atlantic Water into the Arctic happens across the Barents Sea and in the eastern side of Fram Strait. There, the West Spitsbergen Current transports warm water into the Arctic, but about half of the Atlantic Water transported to Fram Strait in the boundary current does not enter the Arctic, but rather recirculates across Fram Strait before joining the East Greenland Current flowing southward. The East Greenland Current is also the major export pathway for solid sea-ice and liquid freshwater out of the Arctic Ocean.

In order to monitor both the heat import to the Arctic Ocean and the sea-ice and freshwater export from the Arctic Ocean, the AWI and the NPI have been maintaining a mooring array across Fram Strait. While the array has experienced some changes over the years, the western side of the array has been operated by the NPI with a focus on the sea-ice and freshwater export while the eastern and central part of the array has been maintained by the AWI with a focus on the warm water import.