New Iceland current could sway N. Atlantic climate

An international team of researchers has confirmed the presence of a deep-reaching ocean circulation system off Iceland that could have “important ramifications” for ocean circulation’s impact on climate in the Northern Hemisphere.



The current, called the North Icelandic Jet (NIJ), contributes to a key component of the Atlantic Meridional Overturning Circulation (AMOC), also known as the “great ocean conveyor belt,” which is critically important for regulating Earth’s climate.



Climate specialists have been concerned that the conveyor belt is
slowing down due to a rise in global temperatures. They suggest that increasing amounts of fresh water from melting ice and other warming-related phenomena are making their way into the northern North Atlantic, where it could freeze, which would prevent the water from sinking and decrease the need for the loop to deliver as much warm water as it does now. Eventually, this could lead to a colder climate in the northern hemisphere. This newly discovered deep, cold current off Iceland's coast may reveal that the North Atlantic is less sensitive to climate change than previously thought.



The "conveyor belt" current, introduced to movie-goers in the Al Gore
environmental film "An Inconvenient Truth," carries warm surface water from the tropical Atlantic toward the Arctic. In the process, the water warms the air in high latitudes, then cools, sinks and returns toward the equator, flowing as a deep stream at lower ocean depths. Crucial to this warm-to-cold oceanographic choreography is the Denmark Strait Overflow Water (DSOW), the largest of the deep, overflow plumes that feed the lower limb of the conveyor belt and return the dense water south through gaps in the Greenland-Scotland Ridge



Climate specialists reckoned that most of the cold water that made up
that deep south-flowing stream came from off the Greenland coast and was made up of fresh glacier-melt water, produced by new warmth in glacier-covered Greenland. However, this view was recently called into question by two oceanographers from Iceland who discovered a deep current flowing southward along the continental slope of Iceland. They named the current the North Icelandic Jet and hypothesized that it formed a significant part of the overflow water.



Now, the team of researchers—including the two Icelanders who discovered it—has confirmed that the Icelandic Jet is not only a major
contributor to the DSOW but “is the primary source of the densest overflow water.”



Because fresh water freezes at a higher temperature than salt water, these specialists suggested that this fresh water from glaciers and other warming-related phenomena would get into the North Atlantic, where it could freeze and prevent the water from sinking to make up the bottom of the conveyor belt.



AMOC RUNNING AMOK?



If that happened, and the AMOC was disrupted or slowed at the place in the far north where the warm water at the surface cools and sinks -- called the overturning -- it could eventually lead to a colder Northern
Hemisphere.



However, the newly confirmed North Icelandic Jet appears to contribute more to the deeper part of the AMOC than the Greenland current does, according to research published in the August 21 online issue of the journal Nature Geoscience.



"Present thinking contends that increased fresh water delivered to the North Atlantic, due to melting ice and increased precipitation under a warming climate, will slow down or halt the overturning" of the AMOC, said study co-author Robert Pickart of Woods Hold Oceanographic Institution.



This might not be the case if the overturning occurs in the interior of the Iceland Sea, which feeds the North Icelandic Jet, Pickart said in an
email interview from Reykjavik.



"It is not inconceivable that this open-ocean process is less sensitive to fresh water forcing than the presently accepted mechanism ... which might lead one to speculate that the deepest part of the overturning may be less sensitive to climate change," he said.



The existence of the NIJ was suspected for decades but was only confirmed recently by Icelandic researchers using underwater velocity
measurements taken from a ship. The NIJ current can't be seen by satellites or detected by its temperature or salinity, but it does move a bit faster than the surrounding water, Pickart said.



Pickart and researchers from Norway and Iceland don't know whether the North Icelandic Jet flows year round or how it varies with time. They are beginning a
research voyage this week to deploy oceanographic instruments to directly measure the NIJ over the course of a full year to try to figure out where and how this current forms.



Picart contends that it is critical that researchers understand the overturning
process to be able to make accurate predictions about the future of climate and circulation interaction. “If a large fraction of the overflow water comes from the NIJ, then we need to re-think how quickly the warm-to-cold conversion of the AMOC occurs, as well as how this process might be altered under a warming climate,” Pickart said.





Source:

Reuters,"New Iceland current could sway N. Atlantic climate", by Deborah Zabarenko, accessed August 22, 2011

Irish Weather Online, "Ocean Current Could Lead To Cooling Of Northern Hemisphere Climate", by Mark Dunply, accessed August 22, 2011

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