Arctic Heat Trap

Scientists from the Alfred Wegener Institute (AWI) have managed to explain the origin of unusually warm water masses in the Arctic. Ocean currents simulated by a computer model explain measurements made during the nineties which indicated unexpected warming but also, in some places, unexpectedly low temperatures. As a result, the circulation of water masses through this section of the world ocean is better understood. The model does not only reproduce data from the past two decades, it can also be used to make predictions. The publication of these findings was included in the recent Highlights list of the American Geophysical Union.

The paper, by Michael Karcher, Rüdiger Gerdes, Frank Kauker and Cornelia Köberle from the AWI, describes the source of unusually warm water masses as a result of a particularly strong phase of the North Atlantic Oscillation (NAO). The NAO describes the oscillation of air pressure differences between Iceland and the Azores. It is linked to variability of air temperatures, precipitation and wind, and also of the oceans. At the end of the eighties it was associated with increased and warmer currents flowing into the Arctic Ocean through the Fram Strait and Barents Sea. The resulting warm anomaly raised questions in the early nineties, when it was described as „Arctic warming“. The water was one to two degrees warmer than expected.

„It was a single event rather than a continual warming process“, comments Karcher. Using a computer simulation with atmospheric data from the past twenty years as input, the AWI researchers calculated that this water circulated for years at between 200 and 1000 metres depth before finally leaving the Arctic.

In 2002, a joint Russian and American team measured surprisingly low temperatures north of the Siberian Laptev Sea, which the model can also explain: The warm anomaly, which reached the Arctic at the beginning of the nineties, has already passed. A second warm anomaly was predicted by the model. In 1999, another warm water mass formed and flowed into the Arctic. This was actually observed by another research team from the AWI during an expedition in the Fram Strait.

„The verification of the model through real measurements shows that we now understand the currents in the Arctic much better. This success is also due in part to the ability to carry out intensive measurements using the ‘Polarstern’ adds Karcher.

The team of authors is currently working on extending the experiment back into the past. The sparse historical data sets of the last 55 years will be used. The team aims to explore the long term variability in ice and ocean conditions in the Arctic. The water masses which they are seeking to understand have a considerable impact on the global oceanic circulation, and hence on climatic changes far beyond the central Arctic.

Bremerhaven, 28.3.2003