On the spatial structure and temporal variability of poleward transport between Scotland and Greenland

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The flow north of warm subtropical water though the northeastern Atlantic is known to have many pathways that vary over time. Here we use a combination of upper ocean current measurements between Greenland and Scotland near 60°N and satellite altimetry to examine the space-time variability of poleward transport. The high-resolution scans of currents in the top 400 m show that the Reykjanes Ridge serves as a very effective separator of flow toward the Nordic and Labrador Seas, respectively. Whereas the Labrador Sea branch exhibits two mean flows to the north on the western slope of the Reykjanes Ridge, the eastern branch flows north in roughly equal amounts over the deep Maury channel and east of Hatton Bank including the Slope Current. There is also a well-defined southward flow along the eastern slope of the Reykjanes Ridge. The satellite altimetric sea surface height (SSH) data show good overall agreement with geostrophically determined -level difference from the repeat ADCP sections (1999-2002), but are unable to resolve the fine structure of the topographically defined mean circulation. The altimetric data show that variations in poleward flow west and east of the Reykjanes Ridge are strongly anticorrelated. They further reveal that the two eastern subbranches also exhibit anticorrelated variability, but offset in time with respect to the Labrador Sea branch. Remarkably, all these variations cancel out for the entire Greenland-Scotland section leaving a gradual decrease in sea-level difference of about 0.06 m over the 1993 to the end of 2010 observation period. Key Points Enormous advantage of repeat current sampling from a vessel in regular traffic The RR is an effective separator of flow toward the Nordic and Labrador Seas A long-term decrease in transport appears to be underway © 2014. American Geophysical Union. All Rights Reserved.

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Journal of Geophysical Research: Oceans