January 23, 2012
Scientists Find An Abundance Of Fresh Water In The Arctic
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A massive pool of fresh water in the Arctic Ocean -- a result of melting ice and river runoff -- has been discovered by British scientists who believe it is expanding and could lower temperatures in Europe by causing the ocean current to slow down.
Scientists from University College London and Britain´s National Oceanography Center found that the western Arctic´s sea surface has risen by 6 inches since 2002. The rise could be due strong Arctic winds accelerating a huge clockwise ocean circulation known as the Beaufort Gyre, which is causing the surface water to bulge.
The Beaufort Gyre is one of the least understood bodies of water on the planet. It is a slowly swirling body of ice and water north of Alaska, about 5 times the size of Tennessee.
The team, using European Space Agency (ESA) satellites ERS-2 and Envisat, measured sea-surface height over the western Arctic over a 15-year period, beginning in 1995 which led to the discovery of the bulge. They found that the volume of fresh water has also swollen by nearly 5000 cubic miles. This accounts for nearly ten percent of all fresh water found in the Arctic Ocean.
Earlier studies from ships, subs and buoy instruments had measured increased volumes of fresh water in the Arctic over the past few decades, and other studies had found that less fresh water was flowing into the Atlantic than expected during the same time period. Those findings suggested water was mostly concentrated in the gyre, and was not spilling into the Atlantic. But those studies also relied on limited observations, not allowing scientists to make good solid estimates at what was driving the changes.
Dr. Katharine Giles from the Center for Polar Observation and Modeling (CPOM) at UCL, lead author of the study, said her team´s findings suggest that a “reversal of the wind could result in the release of this fresh water to the rest of the Arctic Ocean and even beyond.”
Experts say that if the wind changes direction, as has occurred before -- in the mid-1980s and mid-1990s -- the water could spill into the rest of the Arctic and perhaps even the north Atlantic, which in turn could cool Europe by slowing a major ocean current derived from the Gulf Stream, which brings relatively mild air to the continent.
“We were surprised to find that our results also suggested that something else was going on,” Giles told NERC's Planet Earth Online. “When we looked at our data on a year-to-year basis we noticed that the changes in the sea surface height did not always follow what the wind was doing so we thought about reasons why this might happen. One idea is that sea ice forms a barrier between the atmosphere and the ocean. So, as the sea-ice cover changes, the effect of the wind on the ocean might also change.”
Giles said the next step will be to “look into how changes in the sea-ice cover might affect the coupling between the atmosphere and the ocean in more detail to see if we can confirm this idea.”
“Satellites have been measuring how the ice is changing for many years but we now have the tools to monitor how the ocean underneath the ice is changing. These techniques can also be used with the recently launched CryoSat-2 satellite to measure changes over the whole basin,” Dr Seymour Laxon, director of CPOM and co-author of the study, told the agency.
The research results were published in the journal Nature Geoscience on Sunday.
Envisat, the largest Earth observation satellite ever built, will mark 10 years in orbit in March. ERS-2 was retired in July 2011, but data from both it and its predecessor ERS-1 will benefit scientific studies for years to come.
“We were able to produce the Beaufort Gyre results thanks to the overlap of the ERS-2 and Envisat missions and long-term satellite data availability,” said Laxon.
ESA will continue to monitor the Arctic with the upcoming Sentinel series of Earth-observing satellites for Europe´s Global Monitoring for Environment and Security (GMES) program. Later this year, the first results of seasonal changes in sea-ice thickness from data acquired by ESA´s CryoSat-2 satellite will be presented.
Image 2: Arctic Ocean mean sea-surface with respect to the geoid for the past 15 years of satellite radar altimetry data. The Beaufort Gyre is the yellow/orange dome in the Western Arctic. Credits: CPOM/UCL/ESA/Planetary Visions
Image 3: This is a mosaic of Envisat radar images acquired between 9 and 11 September 2011 over the Arctic Ocean. The sea ice extent highlighted in blue corresponds to the areas where more than 80% of the sea surface is covered by ice (from an analysis performed by the US National Ice Center). The Arctic is one of the most inaccessible regions on Earth, so obtaining measurements of sea ice was difficult before the advent of satellites. Credits: ESA/DMI/NIC
On the Net:
- University College London
- Center for Polar Observation and Modeling (CPOM)
- National Oceanography Center
- European Space Agency (ESA)
- Nature Geoscience