The Demark Strait: Looking for the origins of a mysterious current

There is this obscure body of water separating Iceland from Greenland called the Denmark Strait. It’s not very wide, only some 600 miles, but it’s one of the most important stretches of water in the entire world-ocean circulation. Here’s why: Every second of every day millions of cubic meters of warm water flow north along the British Isles and up the coast of Norway aboard an arm of the Gulf Stream System, treating Western Europe to a far more moderate climate than their latitude deserves. However, if all that warm water flows north, an equal quantity of cold water must flow south to maintain the circulation—the stability of our climate depends on it. The narrow Denmark Strait is the main portal for southbound water. Therefore, it’s vital we understand the upstream system that delivers water to the strait.

The accepted theory has held that a current flowing down the East Greenland coast delivered most of the water to the strait. It sounded reasonable. Besides, this region was so under-measured no one had enough data to offer another hypothesis. But then in 2004 two Icelandic oceanographers, Drs. Jonsson and Valdimarsson, found intriguing evidence of an unknown current. That doesn’t happen very often these days; in fact, it’s almost unprecedented. The current seemed to pass over the north slope of Iceland and then flow into the Denmark Strait. The Icelanders were certain enough of its existence to give it a name—the North Icelandic Jet. Then during a follow-on expedition in 2008, WHOI oceanographer Bob Pickart verified its existence with more extensive measurements. Not only is this a new current, not only does it flow into this important Denmark Strait—it supplies fully half the water that exits the strait to form the return-flow current. At least that’s the hypothesis. It remains to be proven. That’s what this cruise is all about.