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Written by fatih al-farahat in , , ,


R. Kwok et al., J. Geophys. Res., 114 (2009): Thinning and volume loss of the Arctic Ocean sea ice cover: 2003–2008

Journal of Geophysical Research - Oceans, 114 (2009) C07005; doi: 10.1029/2009JC005312.

Thinning and volume loss of the Arctic Ocean sea ice cover: 2003–2008

R. Kwok, G. F. Cunningham (Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, U.S.A.), M. Wensnahan (Polar Science Center, Applied Physics Laboratory, University of Washington, Seattle, WA, U.S.A.), I. Rigor (Polar Science Center, Applied Physics Laboratory, University of Washington, Seattle, WA, U.S.A.), H. J. Zwally (Cryospheric Sciences Branch, NASA Goddard Space Flight Center, Greenbelt, MD, U.S.A.), and D. Yi (SGT, Inc., NASA Goddard Space Flight Center, Greenbelt, MD, U.S.A.)

Abstract

We present our best estimate of the thickness and volume of the Arctic Ocean ice cover from 10 Ice, Cloud, and land Elevation Satellite (ICESat) campaigns that span a 5-year period between 2003 and 2008. Derived ice drafts are consistently within 0.5 m of those from a submarine cruise in mid-November of 2005 and 4 years of ice draft profiles from moorings in the Chukchi and Beaufort seas. Along with a more than 42% decrease in multi-year (MY) ice coverage since 2005, there was a remarkable thinning of ∼0.6 m in MY ice thickness over 4 years. In contrast, the average thickness of the seasonal ice in midwinter (∼2 m), which covered more than two-thirds of the Arctic Ocean in 2007, exhibited a negligible trend. Average winter sea ice volume over the period, weighted by a loss of ∼3000 km3 between 2007 and 2008, was ∼14,000 km3. The total MY ice volume in the winter has experienced a net loss of 6300 km3 (>40%) in the 4 years since 2005, while the first-year ice cover gained volume owing to increased overall area coverage. The overall decline in volume and thickness are explained almost entirely by changes in the MY ice cover. Combined with a large decline in MY ice coverage over this short record, there is a reversal in the volumetric and areal contributions of the two ice types to the total volume and area of the Arctic Ocean ice cover. Seasonal ice, having surpassed that of MY ice in winter area coverage and volume, became the dominant ice type. It seems that the near-zero replenishment of the MY ice cover after the summers of 2005 and 2007, an imbalance in the cycle of replenishment and ice export, has played a significant role in the loss of Arctic sea ice volume over the ICESat record.

(Received 2 February 2009, accepted 22 April 2009, published 7 July 2009.)

Kwok, R., G. F. Cunningham, M. Wensnahan, I. Rigor, H. J. Zwally, & D. Yi (2009), Thinning and volume loss of the Arctic Ocean sea ice cover: 2003–2008, Journal of Geophysical Research, 114 (2009) C07005; doi:10.1029/2009JC005312.

Link to abstract: http://www.agu.org/pubs/crossref/2009/2009JC005312.shtml

Written by fatih al-farahat in , ,


NASA's JPL: New NASA ICESat Satellite Survey Reveals Dramatic Arctic Sea Ice Thinning

NEWS RELEASE: 2009-107 July 7, 2009

New NASA Satellite Survey Reveals Dramatic Arctic Sea Ice Thinning

PASADENA, Calif. – Arctic sea ice thinned dramatically between the winters of 2004 and 2008, with thin seasonal ice replacing thick older ice as the dominant type for the first time on record. The new results, based on data from a NASA Earth-orbiting spacecraft, provide further evidence for the rapid, ongoing transformation of the Arctic's ice cover.

Scientists from NASA and the University of Washington in Seattle conducted the most comprehensive survey to date using observations from NASA's Ice, Cloud and land Elevation Satellite, known as ICESat, to make the first basin-wide estimate of the thickness and volume of the Arctic Ocean's ice cover. Ron Kwok of NASA's Jet Propulsion Laboratory in Pasadena, Calif., led the research team, which published its findings July 7 in the Journal of Geophysical Research-Oceans.

The Arctic ice cap grows each winter as the sun sets for several months and intense cold ensues. In the summer, wind and ocean currents cause some of the ice naturally to flow out of the Arctic, while much of it melts in place. But not all of the Arctic ice melts each summer; the thicker, older ice is more likely to survive. Seasonal sea ice usually reaches about 2 m (6 ft.) in thickness, while multi-year ice averages 3 m (9 ft.).

Using ICESat measurements, scientists found that overall Arctic sea ice thinned about 0.17 m (7 in.) a year, for a total of 0.68 m (2.2 ft.) over four winters. The total area covered by the thicker, older "multi-year" ice that has survived one or more summers shrank by 42%.

Previously, scientists relied only on measurements of area to determine how much of the Arctic Ocean is covered in ice, but ICESat makes it possible to monitor ice thickness and volume changes over the entire Arctic Ocean for the first time. The results give scientists a better understanding of the regional distribution of ice and provide better insight into what is happening in the Arctic.

"Ice volume allows us to calculate annual ice production and gives us an inventory of the freshwater and total ice mass stored in Arctic sea ice," said Kwok. "Even in years when the overall extent of sea ice remains stable or grows slightly, the thickness and volume of the ice cover is continuing to decline, making the ice more vulnerable to continued shrinkage. Our data will help scientists better understand how fast the volume of Arctic ice is decreasing and how soon we might see a nearly ice-free Arctic in the summer."

In recent years, the amount of ice replaced in the winter has not been sufficient to offset summer ice losses. The result is more open water in summer, which then absorbs more heat, warming the ocean and further melting the ice. Between 2004 and 2008, multi-year ice cover shrank 1.54 million km² (595,000 sq. miles) -- nearly the size of Alaska's land area.

During the study period, the relative contributions of the two ice types to the total volume of the Arctic's ice cover were reversed. In 2003, 62% of the Arctic's total ice volume was stored in multi-year ice, with 38% stored in first-year seasonal ice. By 2008, 68% of the total ice volume was first-year ice, with 32% multi-year ice.

"One of the main things that has been missing from information about what is happening with sea ice is comprehensive data about ice thickness," said Jay Zwally, study co-author and ICESat project scientist at NASA's Goddard Space Flight Center in Greenbelt, Md. "U.S. Navy submarines provide a long-term, high-resolution record of ice thickness over only parts of the Arctic. The submarine data agree with the ICESat measurements, giving us great confidence in satellites as a way of monitoring thickness across the whole Arctic Basin."

The research team attributes the changes in the overall thickness and volume of Arctic Ocean sea ice to the recent warming and anomalies in patterns of sea ice circulation.

"The near-zero replenishment of the multi-year ice cover, combined with unusual exports of ice out of the Arctic after the summers of 2005 and 2007, have both played significant roles in the loss of Arctic sea ice volume over the ICESat record," said Kwok.

For images of the Arctic sea ice decline, visit: http://www.nasa.gov/topics/earth/features/icesat-20090707.html .

For more information about ICESat, visit: http://icesat.gsfc.nasa.gov .

For more information about NASA and agency programs, visit: http://www.nasa.gov .

JPL is managed for NASA by the California Institute of Technology in Pasadena.

Alan Buis (818) 354-0474, Jet Propulsion Laboratory, Pasadena, CA. Alan.buis@jpl.nasa.gov

Steve Cole (202) 358-0918, NASA Headquarters, Washington. Stephen.e.cole@nasa.gov

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