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

A. J. Watson (), M.-J. Messias, E. Fogelqvist, K. A. Van Scoy, T. Johannessen, K. I. C. Oliver, D. P. Stevens, F. Rey, T. Tanhua, K. A. Olsson, F. Carse, K. Simonsen, J. R. Ledwell, E. Jansen, D. J. Cooper, J. A. Kruepke and E. Guilyardi
Additional contact information
A. J. Watson: School of Environmental Sciences, University of East Anglia
M.-J. Messias: School of Environmental Sciences, University of East Anglia
E. Fogelqvist: Göteborg University
K. A. Van Scoy: Atmospheric and Oceanic Sciences, University of Wisconsin-Madison
T. Johannessen: University of Bergen
K. I. C. Oliver: School of Environmental Sciences, University of East Anglia
D. P. Stevens: School of Mathematics, University of East Anglia
F. Rey: Institute of Marine Research
T. Tanhua: Göteborg University
K. A. Olsson: Göteborg University
F. Carse: School of Environmental Sciences, University of East Anglia
K. Simonsen: The University of the Faroe Islands
J. R. Ledwell: Woods Hole Oceanographic Institution
E. Jansen: University of Bergen
D. J. Cooper: Atmospheric and Oceanic Sciences, University of Wisconsin-Madison
J. A. Kruepke: Atmospheric and Oceanic Sciences, University of Wisconsin-Madison
E. Guilyardi: School of Environmental Sciences, University of East Anglia

Nature, 1999, vol. 401, issue 6756, 902-904

Abstract: Abstract 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 interior1,2. Deep-water formation varies substantially on annual and decadal timescales3,4,5, and responds to regional climate signals such as the North Atlantic Oscillation6,7; its variations may therefore give early warning of changes in the thermohaline circulation that may accompany climate change8. 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 estimated9. 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.

Date: 1999
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DOI: 10.1038/44807

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