Sea ice thickness estimations from ICESat Altimetry over the Bellingshausen and Amundsen Seas, 2003–2009

Abstract

[1] Sea ice thicknesses derived from NASA's Ice, Cloud, and Land Elevation Satellite (ICESat) altimetry data are examined using two different approaches, buoyancy and empirical equations, and at two spatial scales-ICESat footprint size (70 m diameter spot) and Advanced Microwave Scanning Radiometer (AMSR-E) pixel size (12.5 km by 12.5 km) for the Bellingshausen and Amundsen Seas of west Antarctica. Ice thickness from the empirical equation shows reasonable spatial and temporal distribution of ice thickness from 2003 to 2009. Ice thickness from the buoyancy equation, however, additionally needing snow depth information derived from the AMSR-E, shows an overestimation in terms of maximum, mean (+63% to 75%), and standard deviation while underestimation in modal thickness (À20%) as compared with those from the empirical equation approach. When ICESat snow freeboard is used as the snow depth in the buoyancy equation, i.e., the zero ice freeboard assumption, the derived ice thicknesses match well with those from the empirical equation approach, within 5% overall. The AMSR-E, therefore, may underestimate snow depth and accounts for~95% of the ice thickness overestimation as compared with the buoyancy approach. Starting from autumn, a general picture of seasonal mean, modal, and median ice thickness increases progressively from autumn to spring and decreases from spring to the following autumn, when new thin ice dominates the ice thickness distribution. The asymmetric shape of the thickness distribution reflects the key role of ice deformation processes in the evolution of the thickness distribution. The statistical properties of the thickness distribution interannually (high range of mean thickness and standard deviation) indicate the variability of deformation processes. However, spring ice volume, the product of ice mean thickness and areal extent computed for the spring maximum, shows variability year to year but is primarily dominated by ice extent variability, with no increasing or decreasing trend over this record length. The dependence of the volume on the ice extent primarily suggests that ice thickness changes have also not covaried with the ice extent losses seen over the satellite record in this region, unlike the Arctic. These properties reflect the interactive processes of ice advection, thermodynamic growth and ice deformation that all substantially influence ice mass balance in the Bellingshausen-Amundsen Seas region.

About the consistency between Envisat and CryoSat-2 radar freeboard retrieval over Antarctic sea ice

“…A study dealing with the impact that different footprint sizes has on mean and modal freeboard in the Arctic (Schwegmann et al, 2014) showed that differences of 0.1-0.2 m for modal and 0.005 m for mean values can be expected for footprints varying from point measurements, over the ICESat footprint of 70 m to a footprint of 300 m (according to the along-track footprint of CS-2). A similar result was found by Xie et al (2013), who compared sea-ice thicknesses derived from ICESat data on the 70 m ICESat footprint and upscaled to the AMSR-E scale of 12.5 × 12.5 km. Hence, partially, the difference between CS-2 and Envisat mean and modal freeboard may simply be caused by the different footprint and resolution of both measurement systems.…”

“…For this comparison, only data points occurring in both data sets have been taken into account. CS-2 modal freeboard is lower than mean freeboard in all months, like it was also found for sea-ice thickness data from ICESat by Xie et al (2013); Envisat mean and modal freeboard is generally close to each other with modal values being higher than mean values. Mean freeboard shows a seasonal cycle which is comparable for both data products.…”

Summer sea ice characteristics and morphology in the Pacific Arctic sector as observed during the CHINARE 2010 cruise

“…6d): 30 cm, mostly in the MIZ where significant melt occurred into late August, and 130 cm, mostly in the high latitude area, with mean 101 ± 56 cm and median 125 cm for the entire leg, and mean 120 ± 38 cm and median 130 cm for the pack ice zone alone (not shown). None of these two thickness distributions (northward and southward) shows a single peak with long tail to right, which is a common ice thickness distribution from other means such as field measurements and remote sensing (Haas et al, 2008;Wang et al, 2013;Weissling et al, 2011;Xie et al, 2011Xie et al, , 2013Zwally et al, 2008). This behavior indicates that the visual observation of ice thickness (even at the half hourly rate) is still very selective of the level ice thickness and probably undersamples thicker ice.…”

Antarctic Sea-Ice Thickness Retrieval from ICESat: Inter-Comparison of Different Approaches

“…By using data of the Geoscience Laser Altimeter System (GLAS) aboard the Ice, Cloud and land Elevation Satellite (ICESat) Antarctic sea-ice thickness has been estimated in various regions. Markus et al [27] focused on East Antarctic sea ice, Xie et al [28] focused on the Bellingshausen and Amundsen Seas, and Zwally et al [29], Yi et al [30] and Kern and Spreen [31] focused on the Weddell Sea. Kurtz and Markus [32] were the first to provide circum-Antarctic sea-ice thickness and volume estimates based on ICESat data.…”