Unique survey of ocean climate may improve climate predictions

A new letter in Nature Geoscience provides a unique assessment of ocean circulation and climate variability, and thus adds to the basis for improved climate prediction.

A research team from the Nansen Environmental and Remote Sensing Center, and the Bjerknes Centre for Climate Research, both in Bergen, Norway, has studied observed anomalies in ocean climate, and identified the anomalies’ progression with the circulation of the Nordic Seas, and the Norwegian Sea in particular. The Nordic Seas have been much surveyed by, e.g., Norwegian, Faroese, Icelandic, and (Soviet) Russian research vessels since 1950. The present study is the first large-scale synthesis of this rich observational documentation on annual to decadal time scales.

- The traditional and common understanding is that variability in the exchange of water masses between the Nordic Seas and the North Atlantic Ocean is governed by changes in the northern deep waters. Our analysis does not support this concept. We find that anomalies can be traced back to the extension of the Gulf Stream into the Norwegian Sea, says the lead author of the study, dr. Tor Eldevik of the Nansen Center.

The Norwegian study improves the understanding of the Atlantic Ocean’s overturning circulation from a warm Gulf Stream in the surface to a cold return flow at depth. The analysis thus offer a new benchmark for evaluating which ocean regions and observations are the more appropriate for understanding past and present climate change. The study does in particular provide an observational basis for the development of future monitoring or model systems for climate prediction covering the North Atlantic/Nordic Seas region.

- It is a prerequisite for predicting future climate to identify and understand the climate variability of recent decades as documented by the instrumental record. Our study will hopefully be a valuable reference for identifying future change, says Eldevik.

Figure description:
The Atlantic Ocean’s large-scale overturning circulation from warm into cold water masses is a mediator of climate variability and change. The overturning from warm (red) into cold water masses (blue) in the Nordic Seas. The black arrow indicate the extension of the Gulf Stream into the Norwegian Sea, and the gray arrows the cold return flow at depth.

Further information:
Dr. Tor Eldevik, Nansen Environmental and Remote Sensing Center, Bergen, Norway, tor.eldevik-at-nersc.no, tel. +47 55 20 58 00/+47 93 49 40 38

The published letter: Eldevik, T., J.E.Ø. Nilsen, D. Iovino, K.A. Olsson, A.B. Sandø, and H. Drange, 2009: Observed sources and variability of Nordic seas overflow. Nature Geoscience, 2, doi: 10.1038/NGEO518.

The letter was published online 3/5/2009, and will appear in print with the June-issue of Nature Geoscience:


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