Mixing and convection in the Greenland Sea from a tracer-release experiment

Convective vertical mixing in restricted areas of the subpolar oceans, such as the Greenland Sea, is thought to be the process responsible for forming much of the dense water of the ocean interior. Deep-water formation varies substantially on annual and decadal timescales, and responds to regional c...

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Bibliographic Details
Published in:	Nature (London) Vol. 401; no. 6756; pp. 902 - 904
Main Authors:	Watson, A. J, Messias, M.-J, Fogelqvist, E, Van Scoy, K. A, Johannessen, T, Oliver, K. I. C, Stevens, D. P, Rey, F, Tanhua, T, Olsson, K. A, Carse, F, Simonsen, K, Ledwell, J. R, Jansen, E, Cooper, D. J, Kruepke, J. A, Guilyardi, E
Format:	Journal Article
Language:	English
Published:	London Nature Publishing 28-10-1999 Nature Publishing Group
Subjects:	Climate change Convection Deep water Earth, ocean, space Exact sciences and technology Experiments External geophysics Oceans Physics of the oceans Summer Thermohaline circulation Thermohaline structure and circulation. Turbulence and diffusion Water column Water depth Arctic Ocean Greenland Sea United Kingdom > UK United States > US Faroe Islands ANE, Greenland Sea AN, North Atlantic, North Atlantic Oscillation Mixing process Sulfur hexafluoride Ocean convection Turbulent mixing Tracers
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Summary:	Convective vertical mixing in restricted areas of the subpolar oceans, such as the Greenland Sea, is thought to be the process responsible for forming much of the dense water of the ocean interior. Deep-water formation varies substantially on annual and decadal timescales, and responds to regional climate signals such as the North Atlantic Oscillation; its variations may therefore give early warning of changes in the thermohaline circulation that may accompany climate change. Here we report direct measurements of vertical mixing, by convection and by turbulence, from a sulphur hexafluoride tracer-release experiment in the central Greenland Sea gyre. In summer, we found rapid turbulent vertical mixing of about 1.1 cm2 s-1. In the following late winter, part of the water column was mixed more vigorously by convection, indicated by the rising and vertical redistribution of the tracer patch in the centre of the gyre. At the same time, mixing outside the gyre centre was only slightly greater than in summer. The results suggest that about 10% of the water in the gyre centre was vertically transported in convective plumes, which reached from the surface to, at their deepest, 1,200-1,400 m. Convection was limited to a very restricted area, however, and smaller volumes of water were transported to depth than previously estimated. Our results imply that it may be the rapid year-round turbulent mixing, rather than convection, that dominates vertical mixing in the region as a whole.
Bibliography:	ObjectType-Article-2 SourceType-Scholarly Journals-1 ObjectType-Feature-1 content type line 23 ObjectType-Article-1 ObjectType-Feature-2
ISSN:	0028-0836 1476-4687
DOI:	10.1038/44807