Heat and freshwater budgets of the Nordic seas computed from atmospheric reanalysis and ocean observations

Abstract

[1] The heat and freshwater budgets of the Nordic seas are computed from atmospheric reanalysis data and ocean observations, mainly taken during the period 1990-1999. The total heat loss is 198 TW and the freshwater gain 52 mSv (1 Sv = 10 6 m 3 s −1 ), with residuals equal to 1 TW and 3 mSv, respectively. Budgets are also computed for three subregions within the Nordic seas: the Norwegian Sea, the Barents Sea and the Greenland/ Iceland Sea. Without accounting for transfer of heat and freshwater across the Arctic Front, which separates the Greenland/Iceland Sea from the Norwegian Sea, the residuals of the heat and freshwater budgets range from −36 TW to 34 TW and from −16 mSv to 19 mSv, respectively. To close the budgets of all subregions cross-frontal fluxes of −35 TW and 17 mSv, caused either by eddy shedding along the Arctic Front or ocean currents not accounted for, must be included. Combined with observations of the average temperature and salinity on both sides of the Arctic Front these values indicate a rate of cross-frontal water exchange of approximately 4 Sv. The most intense water mass modifications occur in the Norwegian Sea, where ocean heat loss and freshwater input are equal to 119 TW and 41 mSv, respectively.

Mechanisms for decadal scale variability in a simulated Atlantic meridional overturning circulation

“…Vertical heat fluxes of 170 TW (1 TW = 10 12 W) is lost to the atmosphere within the Nordic Seas. This is in good agreement with recent estimates of 197 TW (Segtnan et al 2011). A modest storage anomaly term of -0.05 TW is calculated from the total temperature drift of -0.19°C over the entire 600-year period.…”

“…The external freshwater forcing does not add any volume to the budget, but is rather a ''virtual salt flux'' accounted for by adjusting the salinity according to the forcing. The external freshwater input in the model compares favourably with recent observational-based estimates of around 55 mSv (Dickson et al 2007;Segtnan et al 2011). Note that the model includes river runoff to the Baltic Sea and the North Sea, which is not included for in observational-based estimates.…”

“…This is consistent with the concept first introduced by Mauritzen (1996), where the inflowing Atlantic Water gradually looses buoyancy and sinks as it circulates around the basin. This is due to heat loss (while freshwater forcing partly compensates), as has been shown in several other observational studies (Rudels et al 1999;Segtnan et al 2011).…”

Frontal structures in the West Spitsbergen Current margins

“…Preconditioning to deep water formation, which is possible due to salt transport towards the Greenland Sea, makes the transport of the AW towards the Greenland Sea Gyre especially important. This transport is also necessary to close the heat and freshwater budget of the Greenland Sea (Latarius and Quadfasel, 2010;Segtnan et al, 2011).…”

Along-shelf hydrographic anomalies in the Nordic Seas (1960–2011): locally generated or advective signals?

“…The water masses partly flow through the Nordic Seas to the Arctic Oceans and North Atlantic, respectively, partly mix at the Arctic front, or exchange with the interior basins (Mauritzen et al 2011;Segtnan et al 2011). Variability in the flux and characteristics of these water masses exists on a multitude of temporal and spatial scales (Skagseth et al 2008) and cascades up through the ecosystem, impacting marine species (Hátun et al 2009;Drinkwater 2011).…”