Blog Archive

Friday, May 9, 2008

Arctic Ocean Circulation Does An About-Face



This shows contours of the trend in ocean bottom pressure from 2002 to 2006 as measured by GRACE along with hypothetical trends that would apply at the circles if ocean salinity reverted from 1990s values to climatological conditions over the same period. (Credit: Image courtesy of NASA/Jet Propulsion Laboratory.)


[BLOGGER'S NOTE: This article is from last year, but it is highly relevant to what is going on, at present, in the Arctic sea. From viewing daily satellite images, it seems clear that the circulation is now, again, counter-clockwise. Please comment to correct me, if this assumption is not correct. Also, a wealth of information in the form of maps and graphs related to the Arctic and projections of its climate can be found here: http://maps.grida.no/region/geoarctic ]


ScienceDaily
, Nov. 14, 2007

A team of NASA and university scientists has detected an ongoing reversal in Arctic Ocean circulation triggered by atmospheric circulation changes that vary on decade-long time scales. The results suggest not all the large changes seen in Arctic climate in recent years are a result of long-term trends associated with global warming.

The team, led by James Morison of the University of Washington's Polar Science Center Applied Physics Laboratory, Seattle, used data from an Earth-observing satellite and from deep-sea pressure gauges to monitor Arctic Ocean circulation from 2002 to 2006. They measured changes in the weight of columns of Arctic Ocean water, from the surface to the ocean bottom. That weight is influenced by factors such as the height of the ocean's surface, and its salinity. A saltier ocean is heavier and circulates differently than one with less salt.

The very precise deep-sea gauges were developed with help from the National Oceanic and Atmospheric Administration; the satellite is NASA's Gravity Recovery and Climate Experiment (Grace). The team of scientists found a 10-millibar decrease in water pressure at the bottom of the ocean at the North Pole between 2002 and 2006, equal to removing the weight of 10 centimeters (four inches) of water from the ocean. The distribution and size of the decrease suggest that Arctic Ocean circulation changed from the counterclockwise pattern it exhibited in the 1990s to the clockwise pattern that was dominant prior to 1990.

Reporting in Geophysical Research Letters, the authors attribute the reversal to a weakened Arctic Oscillation, a major atmospheric circulation pattern in the northern hemisphere. The weakening reduced the salinity of the upper ocean near the North Pole, decreasing its weight and changing its circulation.

"Our study confirms many changes seen in upper Arctic Ocean circulation in the 1990s were mostly decadal in nature, rather than trends caused by global warming," said Morison.

"While some 1990s climate trends, such as declines in Arctic sea ice extent, have continued, these results suggest at least for the 'wet' part of the Arctic -- the Arctic Ocean -- circulation reverted to conditions like those prevalent before the 1990s," he added.

The Arctic Oscillation was fairly stable until about 1970, but then varied on more or less decadal time scales, with signs of an underlying upward trend, until the late 1990s, when it again stabilized. During its strong counterclockwise phase in the 1990s, the Arctic environment changed markedly, with the upper Arctic Ocean undergoing major changes that persisted into this century. Many scientists viewed the changes as evidence of an ongoing climate shift, raising concerns about the effects of global warming on the Arctic.

Morison said data gathered by Grace and the bottom pressure gauges since publication of the paper earlier this year highlight how short-lived the ocean circulation changes can be. The newer data indicate the bottom pressure has increased back toward its 2002 level. "The winter of 2006-2007 was another high Arctic Oscillation year and summer sea ice extent reached a new minimum," he said. "It is too early to say, but it looks as though the Arctic Ocean is ready to start swinging back to the counterclockwise circulation pattern of the 1990s again."

Morison cautioned that while the recent decadal-scale changes in the circulation of the Arctic Ocean may not appear to be directly tied to global warming, most climate models predict the Arctic Oscillation will become even more strongly counterclockwise in the future. "The events of the 1990s may well be a preview of how the Arctic will respond over longer periods of time in a warming world," he said.

Grace monitors tiny month-to-month changes in Earth's gravity field caused primarily by the movement of water in Earth's land, ocean, ice and atmosphere reservoirs. As such it can infer changes in the weight of columns of ocean water. In contrast, the pressure gauges installed on the sea floor in 2005-2006 directly measured water pressure at the bottom of the ocean. Gauge data were remotely recovered during the first year of the study.

"The close agreement between the North Pole pressure gauges and Grace data demonstrates Grace's potential for tracking world ocean circulation," said study co-author John Wahr of the University of Colorado, Boulder.

"Satellite altimeters, such as NASA's Jason, are ideal for studying ocean circulation but can't be used at Earth's poles due to ice cover," said study co-author Ron Kwok of NASA's Jet Propulsion Laboratory, Pasadena, Calif. "Our results show Grace can be a powerful tool for tracking changes in the distribution of mass in the Arctic Ocean, as well as its circulation."

Grace is a partnership between NASA and the German Aerospace Center (DLR). The University of Texas Center for Space Research, Austin, has overall mission responsibility. JPL developed the twin satellites. DLR provided the launch, and GeoForschungsZentrum Potsdam, Germany, operates Grace. For more on Grace: http://www.csr.utexas.edu/grace/ .

The study was funded by the National Science Foundation.


Adapted from materials provided by NASA/Jet Propulsion Laboratory.
APA format:

NASA/Jet Propulsion Laboratory (2007, November 14). Arctic Ocean Circulation Does An About-Face. ScienceDaily. Retrieved May 9, 2008, from http://www.sciencedaily.com­ /releases/2007/11/071113200545.htm

Link to article: http://www.sciencedaily.com/releases/2007/11/071113200545.htm

__________________________________________________________________

Here is a graph from 1997 (click to enlarge), from the following site: http://maps.grida.no/go/graphic/ocean_currents_and_sea_ice_extent




7 comments:

SteamGeek said...

As I understand it, the (deep) arctic basin is bisected by a rather distinct and tall mid-basin ridge effectively making the basin two separate bodies of water. I'm assuming the currents reversal of your discussion is more near the surface than overall regarding the depths? Any evidence of volcanic or geothermal activity below the ice cap?

Cassandra_Moderna said...

Well, first, as you know, the Arctic sea doesn't really have an "ice cap." I also think that the U.S. Navy most likely has quite a bit of data, but I am not sure how to locate it. In such a large geographic area there well may be some geothermal and/or volcanic activity, but I really don't know.

My present interest is rather more obscure -- I am looking for maps that show more detail on the currents close to the surface as well as those closer to the bottom, in the more narrow channels, as are found in the Bosporus between the Mediterranean and Black Seas (very much having to do with differences in salinity).

But, the counterclockwise current is not ideal if we would like the ice to hang around longer, as it is drawing up the warm waters coming in from the north Atlantic.

It is a pity that these studies have such long publication delays.

SteamGeek said...

And I'm just an old Industrial Hygiene / Facility Engineering guy with a life long insterest in Earth science, climate, and Ice Ages (and energy management)...

But what do you think of this:

http://news.nationalgeographic.com/news/2003/06/0625_030625_gakkelridge.html

Think it might impact arctic ocean currents, and ice pack cycles?

Cassandra_Moderna said...

That is very interesting, but it is likely to be way too far down to affect the sea surface ice. Have you found any studies on its effects?

http://en.wikipedia.org/wiki/Image:IBCAO_betamap.jpg

What about vulcanism? I kept hearing bits and pieces about Greenland -- do you have links?

SteamGeek said...

Did have some time ago, probobly have links somewhere, but I'm not at my "normal" base right now. I would however, love to continue the discussion later. Pooling resources in the interest of learning more is a good thing.

Cassandra_Moderna said...

I ran across an article not so very long ago that mentioned a researcher who was trying to correlate the onset of El Ninos with those deep sea vents. It was a bit shaky.

SteamGeek said...

Links from my blogging network:

http://www. ucar. edu/communications/newsreleases/2003/volcano. html
http://www. infoplease. com/ipa/A0001762. html
http://www. vulkaner. no/v/volcan/anatahan_e. html
http://www. volcano. si. edu/reports/usgs/
http://www. whoi. edu/home/about/currents9_no1_vailulu. html
http://vulcan. wr. usgs. gov/Volcanoes/SolomonIslands/Maps/map_solomon_islands_volcanoes. html
http://vulcan. wr. usgs. gov/Volcanoes/Tonga/Maps/map_tonga_volcanoes. html
http://vulcan. wr. usgs. gov/Volcanoes/Vanuatu/Maps/map_vanuatu_volcanoes. html
http://vulcan. wr. usgs. gov/Volcanoes/Indonesia/Maps/map_indonesia_volcanoes. html
http://pubs. usgs. gov/gip/dynamic/world_map. html
http://pubs. usgs. gov/gip/dynamic/Hawaiian. html

And on a possible link between melting arctic ice and volcanism...

http://www. volcano. si. edu/world/region. cfm?rnum=17
http://news. nationalgeographic. com/news/2001/11/1129_icebreaker. html
http://www. athropolis. com/arctic-facts/fact-volcanoes. htm
http://seagrant. uaf. edu/news/01ASJ/10. 05. 01seamounts. html