Heat content in the Norwegian Sea, 1995–2010

Abstract

Spatio-temporal hydrographic data from the Nordic Seas during spring over the period 1995–2010 were investigated in terms of the relative heat content (RHC) above the density surface σt = 27.9, chosen to capture the changes in Atlantic water (AW). Focusing on the Atlantic (eastern) domain of the Nordic Seas, negative anomalies dominated the early part of the series. There was then a gradual transition towards an absolute maximum in 2003/2004, followed by a small reduction with positive values for the period ending in 2010. The maps clearly reveal the events of propagating signals. The variability is regionally comparable, but the persistence on a year-to-year basis is higher in the Lofoten Basin than in the Norwegian Basin. Compared with other studies, in this study, the estimated trend in the RHC of the Nordic Seas was larger than for the global mean and the North Atlantic. The warming of the Nordic Seas derives mainly from the advection of warmer inflowing AW and less from changes in local air–sea heat fluxes. The importance of advection suggests that the variability of the Norwegian Sea's ocean climate can, to a large extent, be predicted based on the observed hydrographic conditions.