Possible predictability in overflow from the Denmark Strait

Bob Dickson (), Jens Meincke, Ian Vassie, Johann Jungclaus and Svein Østerhus
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Bob Dickson: Centre for Environment, Fisheries and Aquaculture Science
Jens Meincke: Institut fr Meereskunde, Universitt Hamburg
Ian Vassie: Proudman Oceanographic Laboratory, Bidston Observatory
Johann Jungclaus: Institut fr Meereskunde, Universitt Kiel
Svein Østerhus: Geophysical Institute, University of Bergen

Nature, 1999, vol. 397, issue 6716, 243-246

Abstract: Abstract The overflow and descent of cold dense water from the Denmark Strait sill — a submarine passage between Greenland and Iceland — is a principal means by which the deep ocean is ventilated, and is an important element in the global thermohaline circulation. Previous investigations of its variability — in particular, direct current measurements1,2 in the overflow core since 1986 — have shown surprisingly little evidence of long-term changes in flow speed. Here we report significant changes in the overflow characteristics during the winter of 1996–97, measured using two current-meter moorings and an inverted echo sounder located at different depths in the fastest part of the flow. The overflow warmed to the highest monthly value yet recorded (2.4 °C), and showed a pronounced slowing and thinning at its lower margin. We believe that the extreme warmth of the overflow caused it to run higher on the continental slope off east Greenland, so that the lower current meters and the echo sounder were temporarily outside and deeper than the fast-flowing core; model simulations appear to confirm this interpretation. We suggest that the extreme warmth of the overflow is a lagged response to a warming upstream in the Fram Strait three years earlier (caused by an exceptional amplification of the winter North Atlantic Oscillation). If this is so, overflow characteristics may be predictable.

Date: 1999
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DOI: 10.1038/16680

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