Long-lived vortices as a mode of deep ventilation in the Greenland Sea

Abstract

The Greenland Sea is one of a few sites in the world ocean where convection to great depths occurs1,2,3,4—a process that forms some of the densest waters in the ocean. But the role of deep convective eddies, which result from surface cooling and mixing across density surfaces followed by geostrophic adjustment5, has not been fully taken into account in the description of the initiation and growth of convection6. Here we present tracer, float and hydrographic observations of long-lived (1 year) and compact (5 km core diameter) vortices that reach down to depths of 2 km. The eddies form in winter, near the rim of the Greenland Sea central gyre, and rotate clockwise with periods of a few days. The cores of the observed eddies are constituted from a mixture of modified Atlantic water that is warm and salty with polar water that is cold and fresh. We infer that these submesoscale coherent eddies contribute substantially to the input of Atlantic and polar waters to depths greater than 500 m in the central Greenland Sea.

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Figure 1: The Nordic seas (NS) and an enlargement of the central Greenland Sea (GS).
Figure 2: Time series for the period November 1996–August 1997.
Figure 3: Vertical sections taken along 75° N in May 1997 in the central Greenland Sea.

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Acknowledgements

We thank the staff and crew of RV Håkon Mosby, RV Johan Hjort and RRS James Clark Ross for their support. The main support for this work was from the programmes of the EU: European sub-polar ocean project (ESOP), Tracer and Circulation in the Nordic Seas Region (TRACTOR) and Monitoring the Atlantic Inflow toward the Arctic (MAIA). Additional support from the following national agencies was also important: IFRTP (France), NERC (UK). ESOP required the involvement of a large number of individuals. We thank E. Jansen, coordinator of ESOP 2 and F. Rey for leading the RV Johan Hjort cruise; E. Fogelqvist, T. Tanhua, D. Wallace, C. Rouault and A. Lourenço for their contributions to the tracers and floats programmes respectively. NCEP-NCAR re-analysis data were provided through the NOAA Climate Diagnostics Center.

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Correspondence to Jean-Claude Gascard.

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Gascard, J., Watson, A., Messias, M. et al. Long-lived vortices as a mode of deep ventilation in the Greenland Sea. Nature 416, 525–527 (2002). https://doi.org/10.1038/416525a

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