The Greenland Sea tracer experiment 1996-2002: Horizontal mixing and transport of Greenland Sea Intermediate Water

Messias, M.-J., Watson, A. J., Johannessen, T., Oliver, K. I. C., Olsson, K. A., Fogelqvist, E., Olafsson, J., Bacon, S., Balle, J., Bergman, N., Budeus, G., Danielsen, M., Gascard, J.-C., Jeansson, E., Olafsdottir, S. R., Simonsen, K., Tanhua, T., Van Scoy, K. and Ledwell, J. R. (2008) The Greenland Sea tracer experiment 1996-2002: Horizontal mixing and transport of Greenland Sea Intermediate Water. Progress in Oceanography, 78 (1). pp. 85-105.

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In summer 1996, a tracer release experiment using sulphur hexafluoride (SF6) was launched in the intermediate-depth waters of the central Greenland Sea (GS), to study the mixing and ventilation processes in the region and its role in the northern limb of the Atlantic overturning circulation. Here we describe the hydrographic context of the experiment, the methods adopted and the results from the monitoring of the horizontal tracer spread for the 1996-2002 period documented by ~10 shipboard surveys. The tracer marked "Greenland Sea Arctic Intermediate Water" (GSAIW). This was redistributed in the gyre by variable winter convection penetrating only to mid-depths, reaching at most 1800 m depth during the strongest event observed in 2002. For the first 18 months, the tracer remained mainly in the Greenland Sea. Vigorous horizontal mixing within the Greenland Sea gyre and a tight circulation of the gyre interacting slowly with the other basins under strong topographic influences were identified. We use the tracer distributions to derive the horizontal shear at the scale of the Greenland Sea gyre, and rates of horizontal mixing at ~10 and ~300 km scales. Mixing rates at small scale are high, several times those observed at comparable depths at lower latitudes. Horizontal stirring at the sub-gyre scale is mediated by numerous and vigorous eddies. Evidence obtained during the tracer release suggests that these play an important role in mixing water masses to form the intermediate waters of the central Greenland Sea. By year two, the tracer had entered the surrounding current systems at intermediate depths and small concentrations were in proximity to the overflows into the North Atlantic. After 3 years, the tracer had spread over the Nordic Seas basins. Finally by year six, an intensive large survey provided an overall synoptic documentation of the spreading of the tagged GSAIW in the Nordic Seas. A circulation scheme of the tagged water originating from the centre of the GS is deduced from the horizontal spread of the tracer. We present this circulation and evaluate the transport budgets of the tracer between the GS and the surroundings basins. The overall residence time for the tagged GSAIW in the Greenland Sea was about 2.5 years. We infer an export of intermediate water of GSAIW from the GS of 1 to 1.85 Sv (1 Sv = 106 m3 s-1) for the period from September 1998 to June 2002 based on the evolution of the amount of tracer leaving the GS gyre. There is strong exchange between the Greenland Sea and Arctic Ocean via Fram Strait, but the contribution of the Greenland Sea to the Denmark Strait and Iceland Scotland overflows is modest, probably not exceeding 6% during the period under study

Item Type: Article
Additional Information: Acknowledgements: The Greenland Sea tracer experiment started under the ESOP-2 project (European Sub-Polar Oceans Project, phase 2, supported by the European Commission under MAST III Contract MAS3CT95-0015). The large scale and long term experiment continued under several research project namely ARCICE (Arctic Ice and Environmental Variability supported by Bristish NERC thematique programme), GINS (Greenland–Iceland–Norwegian Seas project, under French INTERPOLE program funded by IFRTP/IPEV), VEINS (Variability of Exchanges in the Northern Seas, European Commission EU programme) and TRACTOR (Tracer and Circulation of the Nordic Seas Region supported by the European Commission under the Fifth Framework Programme Contract No. EVK22000-00080). The Knorr cruise 166/11 was funded by the US NSF and the Oden cruise Arctic Ocean 2002 by the Swedish Polar Secretariat. For their assistance on the tracer measurements, the authors thank Dorothee Bakker, Fiona Carse, David Cooper, Kristina Jönsson, Jo-Anne Kruepke, Malcoam Liddicoat, Gareth Lee, Justin McCarthy, Benoit Mignon, Roger Ling, Marie Persson, Maria Petersson, Sandra Sequeira and Helen Smith.
Faculty \ School: Faculty of Science > School of Environmental Sciences
UEA Research Groups: Faculty of Science > Research Groups > Climate, Ocean and Atmospheric Sciences (former - to 2017)
Faculty of Science > Research Groups > Centre for Ocean and Atmospheric Sciences
Depositing User: Rosie Cullington
Date Deposited: 25 Feb 2011 14:25
Last Modified: 23 Jul 2024 00:13
DOI: 10.1016/j.pocean.2007.06.005

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