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

• Published in: Progress in Oceanography
• Main Authors: 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., Budéus, G., Danielsen, M., Gascard, Jean-Claude, Jeansson, E., Olafsdottir, S. R., Simonsen, K., Tanhua, T., van Scoy, K., Ledwell, J. R.
• Other Authors: School of Environmental Sciences Norwich, University of East Anglia Norwich (UEA), Bjerknes Centre for Climate Research (BCCR), Department of Biological Sciences Bergen (BIO / UiB), University of Bergen (UiB)-University of Bergen (UiB), Department of Chemistry (Göteborg, Suède), Göteborgs Universitet = University of Gothenburg (GU), Marine Research Institute Reykjavik, National Oceanography Centre Southampton (NOC), University of Southampton, Alfred Wegener Institute for Polar and Marine Research (AWI), Laboratoire d'Océanographie et du Climat : Expérimentations et Approches Numériques (LOCEAN), Muséum national d'Histoire naturelle (MNHN)-Institut de Recherche pour le Développement (IRD)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Institut Pierre-Simon-Laplace (IPSL (FR_636)), École normale supérieure - Paris (ENS-PSL), Université Paris Sciences et Lettres (PSL)-Université Paris Sciences et Lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris Diderot - Paris 7 (UPD7)-École polytechnique (X)-Centre National d'Études Spatiales Toulouse (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-École normale supérieure - Paris (ENS-PSL), Université Paris Sciences et Lettres (PSL)-Université Paris Sciences et Lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris Diderot - Paris 7 (UPD7)-École polytechnique (X)-Centre National d'Études Spatiales Toulouse (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS), Nansen Environmental and Remote Sensing Center Bergen (NERSC), Department of Atmospheric and Oceanic Sciences Madison, University of Wisconsin-Madison, Woods Hole Oceanographic Institution (WHOI)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2008
• Subjects: [SDU]Sciences of the Universe [physics]; Arctic; Greenland; Greenland Sea; Nordic Seas; North Atlantic
• Online Access: https://hal.science/hal-04115080; https://doi.org/10.1016/j.pocean.2007.06.005

International audience In summer 1996, a tracer release experiment using sulphur hexafluoride (SF 6 ) 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 ...