Arctic warming - Evolution and Spreading of the 1990s warm event in the Nordic Seas and the Arctic Ocean,

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Karcher, M. , Gerdes, R. , Kauker, F. and Köberle, C. (2003): Arctic warming - Evolution and Spreading of the 1990s warm event in the Nordic Seas and the Arctic Ocean, , Journal of Geophysical Research, Vol. 108(C2) . doi: 10.1029/2001JC001265
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Observations in the Arctic Ocean have revealed changes in oceanic temperature, salinity and the ice cover of the 1990s in comparison to earlier data. With a numerical model we hindcast the coupled ice-ocean system of the Arctic and sub-Arctic seas for the past two decades to improve the scientific understanding of their modes of response to atmospheric forcing. The model is driven by atmospheric data from the ECMWF reanalysis between 1979 a nd 1993 and from the ECMWF analysis between 1994 and 1999. The focus of the work presented here is on the temperature rise which occurred in the Atlantic layer of the Arctic Ocean in the early 1990s.The model favorably reproduces the development and subsequent propagation of temperature anomalies in the water of Atlantic origin in the Northwest European Shelf area and along the Norwegian coast. These anomalies propagate into the Arctic Ocean via the Barents Sea and the Fram Strait. Two warm anomalies are entering the Arctic Ocean through these passages between 1983 and 1985 and between 1989 and 1994, respectively. While the first smaller anomaly only warms up the western Eurasian Basin, the second large anomaly spreads far into the eastern Eurasian Basin and across the Lomonossov Ridge into the western Arctic basins.Intensified boundary currents during the high NAO state in the first half of the 1990s significantly influence amplitude and speed of the temperature anomalies inside the Arctic Ocean. In contrast to the notion of a continuos warming process during the 1990s our model results suggest the warming of the Atlantic Layer in the Arctic Ocean to happen in the form of events. The event with the largest anomalous heat input during the modeled period entered the Arctic between 1989 and 1994. It delivers an additional heat of about 30 TW to the Arctic Ocean proper compared to most of the 1980s. In the analysis of the model results it is possible to trace back this surplus of heat input to the Arctic to an increased volume inflow via the Faroer-Scotland passage and a reduced heat loss to the atmosphere in the late 1980s and early 1990s.We conclude that apart from the intrusion of anomalously warm water also the strong intensification of the cyclonic circulation in the Nordic Seas and the Eurasian Basin is responsible for the rapid warming of the Arctic boundary current in the early 1990s. After a reduction of warm water inflow into the Arctic Ocean in the second half of the 1990s, the most recent observations and the model results point to a recurrence of a warm anomaly in the inflow from 1999 onwards.

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