Task 3.3: Bifurcation of the Norwegian Atlantic Current into a Barents Sea and a Fram Strait path

Main objective The overall objective of this task is to improve the understanding of the mechanisms governing the bifurcation of the NwAC into the Barents Sea and to the West Spitzbergen Current (WSC) and use this as basis for interpretation of observed variations in the Arctic.

The NwAC divides into a WSC branch and a Barents Sea branch at about 73oN, just north of the Gimsøy section. The relative distribution of these branches is besides being determining for the local climate of the Barents Sea, also fundamentally important for the heat budget of the Arctic Ocean. This is because AW is cooled to near the freezing point in the Barents Sea before cascading into the Arctic at some intermediate depth (Midttun, 1985; Blindheim, 1989), whereas AW in the WSC subducts below fresher Arctic water at about west of Bear Island and thus basically preserves its heat as advected into the Arctic.

Dependent on what is the governing mechanism for the bifurcation the effect on the biology maybe quite differently as for the physical climate. This is simply because the physical ocean climate is basically an integrated effect of sources and sinks, whereas for the distribution of particular biological species the important factor may be the actual currents at some specific period. An example related to this task is the larvae and pelagic juveniles of Arcto-Norwegian cod that after the winter spawning in the Lofoten-Vesterålen area drift northward with the NwAC and the Norwegian Coastal Current (NCC). In late winter/early spring the they are in the region of the Tromsøflaket, and variations in the atmospheric forcing and the currents during this particular period have a large effect on the their distribution (Vikebø et al., 2005).

Proposed activity

The gathered data under activity 1.4 and 1.5 will, together with other available data, be synthesized to investigate the control of both the mean state and the variability. In terms of variability will seek causal relations between variations in the atmospheric forcing and the bifurcation of the current into the two branches, and investigate the role of local topography in creating waves and eddies that can affect the two branches (Skagseth and Orvik, 2002). Data from a larger region will be included to investigate the role of non-local oceanic and atmospheric dynamics.  An eddy resolving Regional Ocean Model System (Budgell, 2005) will be used as a central tool; both performing idealized simulations and forced with atmospheric reanalysis data.
 
Links: The proposed activity related to the bifurcation of the NWAC at 73°N (WP 1.5, 3.3), and the monitoring in the Fugløya Bear Island section is closely linked and provide input to a number of other IPY proposals: ESSAR- lead by K. Drinkwater focusing on fronts in the Barents Sea, BIAC- lead by T. Gammelsrød focusing on the dense-water formation in the Barents Sea where these data provide the necessary upstream input, and IPY-PanAME lead by Stig Falk-Petersen where biological sampling is planned in Fugløya-Bjørnøya.