Abstract
Abstract. A combined interpretation of synthetic aperture radar (SAR) satellite images and helicopter electromagnetic (HEM) sea-ice thickness data has provided an estimate of sea-ice volume formed in Laptev Sea polynyas during the winter of 2007/08. The evolution of the surveyed sea-ice areas, which were formed between late December 2007 and middle April 2008, was tracked using a series of SAR images with a sampling interval of 2–3 days. Approximately 160 km of HEM data recorded in April 2008 provided sea-ice thicknesses along profiles that transected sea ice varying in age from 1 to 116 days. For the volume estimates, thickness information along the HEM profiles was extrapolated to zones of the same age. The error of areal mean thickness information was estimated to be between 0.2 m for younger ice and up to 1.55 m for older ice, with the primary error source being the spatially limited HEM coverage. Our results have demonstrated that the modal thicknesses and mean thicknesses of level ice correlated with the sea-ice age, but that varying dynamic and thermodynamic sea-ice growth conditions resulted in a rather heterogeneous sea-ice thickness distribution on scales of tens of kilometers. Taking all uncertainties into account, total sea-ice area and volume produced within the entire surveyed area were 52 650 km2 and 93.6 ± 26.6 km3. The surveyed polynya contributed 2.0 ± 0.5% of the sea-ice produced throughout the Arctic during the 2007/08 winter. The SAR-HEM volume estimate compares well with the 112 km3 ice production calculated with a~high-resolution ocean sea-ice model. Measured modal and mean-level ice thicknesses correlate with calculated freezing-degree-day thicknesses with a factor of 0.87–0.89, which was too low to justify the assumption of homogeneous thermodynamic growth conditions in the area, or indicates a strong dynamic thickening of level ice by rafting of even thicker ice.
Highlights
The coastal regions of the Arctic Ocean are characterized by transition zones between landfast and freely drifting sea ice during wintertime
Accord-The spatial and temporal evolution of the tracked sea ice pro- ing to the synthetic aperture radar (SAR) images, this 16-day-old ice began forming on duced during the four polynya events is shown in Figs. 3 and March 28, and convergence with surrounding floes on March
It was followed by the second event heavily deformed ice at the end of January when ∼ 12 000 km2 of sea ice formed within 9 days
Summary
The coastal regions of the Arctic Ocean are characterized by transition zones between landfast and freely drifting sea ice during wintertime. The majority of Arctic polynyas reoccur along the coasts of Siberia, Alaska, and the western Canadian archipelago. The quasi-perennial polynyas of the Laptev Sea extend almost 2000 km along the coast and can be several hundred kilometers wide. After initial freeze-up and before the onset of melting, the formation of sea-ice area in the Arctic Ocean is limited to polynyas and leads in the seaice cover. Their importance for the maintenance of the Arctic sea-ice volume and their impact on stratification in the Arctic Ocean is not completely understood
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