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Significant role of the North Icelandic Jet in the formation of Denmark Strait overflow water

Abstract

The Denmark Strait overflow water is the largest dense water plume from the Nordic seas to feed the lower limb of the Atlantic Meridional Overturning Circulation. Its primary source is commonly thought to be the East Greenland Current. However, the recent discovery of the North Icelandic Jet—a deep-reaching current that flows along the continental slope of Iceland—has called this view into question. Here we present high-resolution measurements of hydrography and velocity north of Iceland, taken during two shipboard surveys in October 2008 and August 2009. We find that the North Icelandic Jet advects overflow water into the Denmark Strait and constitutes a pathway that is distinct from the East Greenland Current. We estimate that the jet supplies about half of the total overflow transport, and infer that it is the primary source of the densest overflow water. Simulations with an ocean general circulation model suggest that the import of warm, salty water from the North Icelandic Irminger Current and water-mass transformation in the interior Iceland Sea are critical to the formation of the jet. We surmise that the timescale for the renewal of the deepest water in the meridional overturning cell, and its sensitivity to changes in climate, could be different than presently envisaged.

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Figure 1: Flow through the Denmark Strait.
Figure 2: Hydrographic properties along the Látrabjarg line near the sill as measured during the October 2008 survey.
Figure 3: Flow of dense water upstream of the Denmark Strait.
Figure 4: Model circulation and hydrography.

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Acknowledgements

The authors wish to thank B. Rudels and J. B. Girton for comments. Support for this work was provided by the US National Science Foundation and the Research Council of Norway. This is publication A351 from the Bjerknes Centre for Climate Research.

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K.V., R.S.P., H.V., S.J. and D.J.T. collected and analysed the data; M.A.S. designed and analysed the model simulations; K.V., R.S.P. and M.A.S. wrote the paper and all authors interpreted the results and clarified the implications.

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Correspondence to Kjetil Våge.

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Våge, K., Pickart, R., Spall, M. et al. Significant role of the North Icelandic Jet in the formation of Denmark Strait overflow water. Nature Geosci 4, 723–727 (2011). https://doi.org/10.1038/ngeo1234

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