13 September 2017: FB1 seminar

14:00, lecture hall west, Düsternbrooker Weg 20

Abstract:

The Fram Strait is the deepest and widest gateway connecting the Arctic Ocean with the Nordic Seas and thereby the North Atlantic. It is characterized by strong gradients in temperature and salinity: The warm and salty West Spitsbergen Current (WSC), transporting Atlantic Water (AW) northward, encounters the cold and fresh East Greenland Current (EGC), transporting Polar Water (PW) southward.  Eddy driven recirculation of AW in the Fram Strait modifies the amount of heat that reaches the Arctic Ocean, but is difficult to constrain in ocean models due to very small Rossby radius there.

 In this presentation I focus on the effect of resolved eddies on the AW circulation in a locally eddy-resolving simulation of the global Finite-Element-Sea ice-Ocean-Model (FESOM). An eddy-permitting simulation serves as a control run. Results suggest that resolving local eddy dynamics is critical to realistically simulate ocean dynamics in the Fram Strait. Strong eddy activity simulated by the eddy-resolving model, with peak in winter and lower values in summer, is comparable in magnitude and seasonal cycle to observations from a long-term mooring array, whereas the eddy-permitting simulation underestimates the observed magnitude. Furthermore, a strong cold bias in the central Fram Strait present in the eddy-permitting simulation is reduced due to resolved eddy dynamics, and AW transport into the Arctic Ocean is increased with possible implications for the Arctic Ocean heat budget.

For decades biological, chemical, and physical oceanographic as well as benthic studies have been conducted in the Fram Strait. An ocean-sea ice model that represents the processes occurring there is extremely valuable, since it helps to interpret the measurements and fill gaps that point-wise measurements inevitably leave. The eddy-resolving model configuration presented here can be used for many different applications. For example, it helps to interpret particle fluxes measured by sediment traps attached to moorings in the Fram Strait. Computation of backward trajectories can identify the catchment areas, which reveals the origin of particles.

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