Sea ice freeboard in McMurdo Sound, Antarctica, derived by surface-validated ICESat laser altimeter data

Abstract

Method-1 (M-1) follows those previously presented in the literature using the lowest elevations to construct an estimate of sea surface height. However, the lack of leads in the study area motivated the development of Method-2 (M-2) which utilizes tide models. Each year is divided into two investigation periods from September to December and February to June, and these investigations were further segmented by sea ice type, first-year (FY), and multiyear (MY). Both applied methods reveal a statistically significant linear increase in multiyear sea ice freeboard. For M-1, the mean freeboard increased over the study period from 0.53 to 1.00 m and for M-2 from 0.46 to 0.95 m. Evidence is presented that the multiyear sea ice freeboard increase is strongly linked to the development and incorporation of a subice platelet layer. No statistically significant trends were observed for first-year sea ice. ICESat derived freeboards over first-year and multiyear sea ice areas compare within one standard deviation of airborne measured freeboard in November 2009.

Observed platelet ice distributions in Antarctic sea ice: An index for ocean‐ice shelf heat flux

“…Under first year sea ice, it has been shown that it is possible to detect the sub‐ice platelet layer using electromagnetic induction techniques [ Rack et al , ; Hunkeler et al , ], and this offers promise for more extensive surveys using aircraft. Currently the indirect detection of the platelet layer is at the limits of resolution for satellite altimetry [ Price et al , ], although it is indicated that a thick sub‐ice platelet layer beneath coastal fast ice is identifiable in McMurdo Sound, where freeboard anomalies were found to coincide with the sub‐ice platelet layer [ Price et al , ]. However, if airborne and satellite remote sensing estimates of the extent of influence of ISW are to be made, they need to be supported by in situ observation, and supplemented by modeling at a range of scales.…”

Airborne thickness and freeboard measurements over the McMurdo Ice Shelf, Antarctica, and implications for ice density

“…The cross sections with the highest densities are close to an area near the front of the ice shelf where the highest relative abundance of subice platelets has been found beneath sea ice [ Dempsey et al ., ]. ICESat freeboard measurements between 2003 and 2009 show that fast ice in this area experienced the greatest rate of increase in freeboard, which was interpreted as a consequence of basal freezing due to the outflow of cold Ice Shelf Water [ Price et al ., ].…”

The sub-ice platelet layer and its influence on freeboard to thickness conversion of Antarctic sea ice

“…The influence of this plume on sea ice processes has been documented in studies of sea ice structure and growth Dempsey et al, 2010;Mahoney et al, 2011;Gough et al, 2012). Satellite altimeter observations have indicated that the locations of the largest increases in multiyear sea ice thickness from 2003-2009 during the NASA ICESat mission (Price et al, 2013) were coincident with the greatest abundance of platelet ice (Dempsey et al, 2010). This region has recently been identified as the location of an ISW plume (Robinson et al, 2014).…”

“…In the simplest sense the difference between altimetric measurements of the local sea surface height and the sea ice elevation provides the freeboard, which can be used in conjunction with snow depth and the densities of ice and snow to estimate sea ice thickness (Zwally et al, 2008;Kurtz and Markus, 2012;Price et al, 2013). The additional influence of the sub-ice platelet layer has not yet been considered.…”