Surveys of the Nordic seas spanning more than 100 years reveal that warm water from the North Atlantic flows along the eastern margin of the Nordic seas while cold water from the Arctic flows south along the east coast of Greenland. However, the temperature differences in the deep waters are small and give little information on how the deep water circulates within these basins. From theory we know that the shape of the ocean bottom significantly constrains fluid motion in the deep waters, but a limited number of direct measurements leave the flow pattern and strength mainly unknown in the Nordic Seas.
Twenty five subsurface drifters tracking the currents
In order to study the deep flow, we deployed 25 neutrally buoyant subsurface drifting floats across the northern slope of the Iceland–Faroe Ridge at a depth of 800 m in the fall of 2004. The floats drifted with the flow for 18 months and surfaced in the spring of 2006. During their 18 month journey the floats recorded temperature, pressure and reception times of acoustic signals from moored low frequency sound sources. The acoustics signals enable us to calculate 2 positions per day and construct complete subsurface trajectories for the 18 month period.
Revealing the secret behind the ocean currents paths
We found that the movement of the floats was tightly controlled by topography such that flow of intermediate waters within and the exchange between the basins took place along depth contours. By contrast, just upstream of the outflow of intermediate water from the Nordic seas to the North Atlantic, the flow is forced to cross depth contours. As a result, the flow becomes conspicuously unstable with strong eddy motion in the Faroe–Shetland Channel.
Increasing the understanding of the ocean circulation
It has long been known that cold deep water from the Nordic Seas flow into the Atlantic and forms the bottom water and that this is an important contribution to the deep circulation in the Atlantic Ocean. In this study it has been shown that the deep water flows in a narrow current along the topography in the Nordic Seas. This is new knowledge that contributes to the fundamental understanding of the circulation and it also points to key areas for monitoring of potential changes is the deep circulation due to a warming climate.
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Reference:
¹Institute of Marine Research and Bjerknes Centre for Climate Research, Norway
²Graduate School of Oceanography, University of Rhode Island,
USA
³Graduate School of Oceanography, University of Rhode Island,
USA