Annual and interannual variability of Atlantic Water temperatures in the Norwegian and Barents Seas: 1980–1996

Changes in the oceanographic climate of the Arctic Ocean during the 1990s have been linked to anomalous heat and volume transports of Atlantic Water (AW) from the Nordic Seas. This paper focuses on the variability in the AW temperature in the Norwegian Sea and in the Barents Sea Opening (BSO), using 16 years of data from five regular hydrographic sections across the flow of AW from the Faroe–Shetland inflowing area to the Barents Sea and Fram Strait. In a section across the BSO, data from 102 surveys were analysed. Here time series for mean temperatures and salinities are constructed for 10, 50, 100, 200, 300, and 400 m depths. While seasonal- and shorter-period variability has largest amplitudes in the water masses above 200 m depth, interannual variability in temperature has largest amplitudes near the bottom. At 400 m depth, the amplitudes of the interannual variations are of the order of 1°C and exceed the magnitude of the seasonal cycle. Two warm periods, 1983–1984 (W1) and 1990–1992 (W2), and one cold period, 1986–1988 (C1), are discussed. W1 and partly C1 can be traced back to the Iceland–Scotland Gap, from where they were advected with the mean flow of AW northwards along the eastern flank of the Nordic Seas. The temperature anomalies decreased in magnitude while they moved towards the north. W2 had a different characteristic, as it can be explained by reduced heat loss to the atmosphere, or by an increased advection speed, within the Nordic Seas. The anomaly was strengthened along the flow towards the north. The salinity anomalies were advected with the AW and strengthened by fresh-water fluxes along their pathway inside the Nordic Seas. In the BSO the temperature anomalies indicate that the AW inflow to the Barents Sea occurs in two branches along the southern slope of the BSO. The anomalies are recirculated in the Barents Sea and return to the BSO along the northern slope of the section.