For many years, it was thought that the primary source of the Denmark Strait Overflow Water (DSOW) – a large, deep plume of water that forms part of the ‘great ocean conveyor belt’, returning dense water south through gaps in the Greenland-Scotland Ridge – is a current adjacent to Greenland known as the East Greenland Current. However, two oceanographers from Iceland recently called this into question when they discovered a deep current flowing southward along the continental slope of Iceland, which they named the North Icelandic Jet (NIJ).

In a paper published in Nature Geoscience, the researchers have confirmed that the NIJ is not only a major contributor to the DSOW but ‘is the primary source of the densest overflow water’. ‘Our data demonstrate that the NIJ indeed carries overflow water into Denmark Strait and is distinct from the East Greenland Current,’ said one of the study’s authors, Robert S Pickart of the Woods Hole Oceanographic Institution. ‘We show that the NIJ constitutes approximately half of the total overflow transport and nearly all of the densest component.’

The results, Pickart said, have ‘important ramifications’ for the impact of ocean circulation on climate. Climate scientists have previously raised concerns that the conveyor belt is slowing down due to a rise in global temperatures. ‘If a large fraction of the overflow water comes from the NIJ, then we need to rethink how quickly the warm-to-cold conversion of the Atlantic Meridional Overturning Circulation occurs, as well as how this process might be altered under a warming climate,’ Pickart said.

October 2011