Community Research and Development Information Service - CORDIS

Data of Lagrangian floats deployed in the Norwegian Sea during the years 2002-2005

Neutrally buoyant floats are devices that drift with the currents and thereby track the water pathways. During ASOF-N standard RAFOS floats were used. They were equipped with acoustic receivers tuned to the same frequency as the SOFAR sound sources installed on 13 moorings. The floats' acoustic receivers are detecting the time of arrivals (TOA) of signals transmitted regularly by the SOFAR sources. With these TOAs the position of the floats is tracked underwater acoustically. Thirty-eight floats were ballasted to drift at depths of about 300m and an additional four floats were ballasted to drift at 1000m. The floats were deployed west of the Lofoten Islands, across the Norwegian Atlantic Current and close to the continental slope. After drifting for approximately 6 months, the floats were released to pop up at the surface, where they transmitted via satellite the data recorded during the previous 6 months. During this transmission the floats also recorded in situ temperature and pressure.

Of the 38 floats ballasted for 300m, 25 transmitted data. While in general the data transmission rate was very good (of 24 floats deployed between spring 2003 and 2004 only 3 were lost) all ten floats deployed in November 2004 were lost. The best explanation to account for this strange loss is that they got transported northward by a current surge and got stuck under the ice cover. This would then indicate that in winter 2004 none of floats got transported into the Barents Sea, where they would have been safe but all ten floats got transported into Fram Strait.

During ASOF-N the balance depth was increased to 300m as previous experience from the MAIA project showed that this is the depth were the core of Atlantic water is found. The 5 float deployments made during ASOF-N means that for the first time variability between the years can be traced. During the predecessor project MAIA only 1 deployment of 5 floats took place. The measurements with floats made during ASOF-N showed that the Atlantic current is not restricted to a swift boundary current (like a jet) but more like a broad current dominated by mesoscale eddies.

Users interested in the result:
Oceanographer, especially scientists interested in Arctic ocean research, Scientists investigating ocean circulation, Scientist studying the interactions of water circulation and climate.

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