Search

Unlike the rapid sea ice losses reported in the Arctic, satellite observations show an overall increase in Antarctic sea ice concentration over recent decades. However, observations of decadal trends in Antarctic ice thickness, and hence ice volume, do not currently exist. In this study a model of the Southern Ocean and its sea ice, forced by atmospheric reanalyses, is used to assess 1992-2010 trends in ice thickness and volume. The model successfully reproduces observations of mean ice concentration, thickness, and drift, and decadal trends in ice concentration and drift, imparting some confidence in the hindcasted trends in ice thickness. The model suggests that overall Antarctic sea ice volume has increased by approximately 30 km3 yr−1 (0.4% yr−1) as an equal result of areal expansion (20 × 103 km2 yr−1 or 0.2% yr−1) and thickening (1.5 mm yr−1 or 0.2% yr−1). This ice volume increase is an order of magnitude smaller than the Arctic decrease, and about half the size of the increased freshwater supply from the Antarctic Ice Sheet. Similarly to the observed ice concentration trends, the small overall increase in modeled ice volume is actually the residual of much larger opposing regional trends. Thickness changes near the ice edge follow observed concentration changes, with increasing concentration corresponding to increased thickness. Ice thickness increases are also found in the inner pack in the Amundsen and Weddell Seas, where the model suggests that observed ice-drift trends directed toward the coast have caused dynamical thickening in autumn and winter. Modeled changes are predominantly dynamic in origin in the Pacific sector and thermodynamic elsewhere. [ABSTRACT FROM AUTHOR]

Abstract: Since 2009, subsets of declassified satellite images of Arctic sea ice have been released as literal image derived products (LIDPs) with one-meter resolution for scientific use. The collections include imagery acquired over six fixed locations in the Arctic Basin since 1999. Targeted acquisitions over drifting ice parcels, from 2009 on, provide an added dimension to the LIDP archive. This mode of acquisition is especially useful for capturing time-varying processes during the melt season. In this paper, we describe the characteristics of LIDPs, the extent of the current archive, and highlight their uses for Arctic sea ice science. At this writing, the archive of LIDPs is still quite limited, and thus this paper illustrates the potential utility of the imagery. We provide an overview of the retrieval of five sea ice parameters that would benefit significantly from the surface details afforded by the higher resolution LIDPs. They include: melt pond coverage, open water fraction, ridge height, floe size, and, openings and closings. Two other uses are suggested: measurement of lateral melt and the interpretation of radar backscatter. The intent is to motivate geophysical uses of the LIDP and future acquisitions. Results here suggest that the effective observations of sea ice parameters and especially their changes require more focused sampling strategies to address specific spatial and temporal sampling needs. Presently, acquisitions of this type of imagery at fixed locations and drifting sites are being continued, and LIDPs are added to the archive as they are released. [Copyright &y& Elsevier]

Freshening in the Canada basin of the Arctic Ocean began in the 1990s and continued to at least the end of 2008. By then, the Arctic Ocean might have gained four times as much fresh water as comprised the Great Salinity Anomalyof the 1970s, raising the spectre of slowing global ocean circulation. Freshening has been attributed to increased sea ice melting and contributions from runoff, but a leading explanation has been a strengthening of the Beaufort High-a characteristic peak in sea level atmospheric pressure-which tends to accelerate an anticyclonic (clockwise) wind pattern causing convergence of fresh surface water. Limited observations have made this explanation difficult to verify, and observations of increasing freshwater content under a weakened Beaufort High suggest that other factors must be affecting freshwater content. Here we use observations to show that during a time of record reductions in ice extent from 2005 to 2008, the dominant freshwater content changes were an increase in the Canada basin balanced by a decrease in the Eurasian basin. Observations are drawn from satellite data (sea surface height and ocean-bottom pressure) and in situ data. The freshwater changes were due to a cyclonic (anticlockwise) shift in the ocean pathway of Eurasian runoff forced by strengthening of the west-to-east Northern Hemisphere atmospheric circulation characterized by an increased Arctic Oscillation index. Our results confirm that runoff is an important influence on the Arctic Ocean and establish that the spatial and temporal manifestations of the runoff pathways are modulated by the Arctic Oscillation, rather than the strength of the wind-driven Beaufort Gyre circulation. [ABSTRACT FROM AUTHOR]