Arctic sea ice retreat in 2007 follows thinning trend

Journal of Climate (Impact Factor: 4.9). 01/2009; DOI: 10.1175/2008JCLI2521.1

ABSTRACT The minimum of Arctic sea ice extent in the summer of 2007 was unprecedented in the historical record. A coupled ice–ocean model is used to determine the state of the ice and ocean over the past 29 yr to investigate the causes of this ice extent minimum within a historical perspective. It is found that even though the 2007 ice extent was strongly anomalous, the loss in total ice mass was not. Rather, the 2007 ice mass loss is largely consistent with a steady decrease in ice thickness that began in 1987. Since then, the simulated mean September ice thickness within the Arctic Ocean has declined from 3.7 to 2.6 m at a rate of 0.57 m decade 1 . Both the area coverage of thin ice at the beginning of the melt season and the total volume of ice lost in the summer have been steadily increasing. The combined impact of these two trends caused a large reduction in the September mean ice concentration in the Arctic Ocean. This created conditions during the summer of 2007 that allowed persistent winds to push the remaining ice from the Pacific side to the Atlantic side of the basin and more than usual into the Greenland Sea. This exposed large areas of open water, resulting in the record ice extent anomaly.

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    ABSTRACT: Intellectual Merit This proposal seeks support to test the hypothesis that the dynamics of Nares Strait is in a state of transition as the season of landfast ice cover diminishes. To do so, we propose to analyze a comprehensive 6-year data set from an array of moored ocean current, salinity, temperature, sea level, and subsurface pressure sensors, as well as ice thickness observations. The data originate from an unprecedented, high-risk, but ulti-mately successful 2003-2009 Canada-US observational program that took place in Nares Strait, a major pathway of Arctic waters into the North Atlantic to the west of Green-land. We propose to describe and explain the temporally and spatially varying regimes of kinematics and dynamics within this energetic channel. As oceanic fields are forced by vertical and horizontal boundary layer physics at the ice-water, air-water, and ice-air interfaces, the program includes synthesis of data from a meteorological modeling, a remotely-sensed ice (MODIS), and an ice modeling (CICE) component. The moored array was deployed in 2003, serviced in 2006 and 2007, and finally recov-ered in 2009. unchow and Melling (2008) and Rabe et al. (2010) present first results on the depth-averaged ocean currents and vertical stratification of salinity and temperature, respectively, for the 2003-06 period. The second 2007-09 deployment resulted in a com-plete record as all instruments were recovered without any gaps. These data allow us to test the hypothesis that the freshwater flux through the Canadian Archipelago presently transitions from a dynamic state that is characterized by land-fast ice to one that is char-acterized by mobile ice. This regime change causes more variable ice and ocean motion as well as potential increase in freshwater flux by 50%, because the system responds more strongly to time-dependent local atmospheric forcing in addition to remote forcing. Tem-poral variations of ocean stratification and freshwater flux take place at spatial scales that include fundamental geophysical scales for fluids under the influence of rotation (Rossby radius of deformation), geometric scales set by topography, and scales related to vertical and lateral boundary layer processes such as friction. Broader Impacts The proposed effort will support first-year Ph.D students Patricia Ryan and Jamie Shutta in addition to two undergraduate and two local science teachers as summer interns with the PIs facilitating daily workshops. The education of students and teachers to critically evaluate physical and statistical methods, data, and analyses is needed to improve both public and scientific debate related to climate change. This proposal contributes substantially to US participation, continuity, and data dissemina-tion within an ongoing, informal, international, collaborative effort of a "Friends of Nares Strait" group that includes young and old researchers from Denmark, Scotland, England, Canada, and the USA. Canadian, Danish, and US government agencies and private ser-vice providers frequently rely on our data and expertise in order to aid their clients, e.g. with oil exploration, icebreaking operations, or natural resource management.

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