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

Previous investigations have linked changes in the multiyear sea ice area of McMurdo Sound, Antarctica, from 1213 km(2) in 2003 to 4923 km(2) in 2005, to the passage of large tabular icebergs preventing the annual sea ice breakout. This maximum coverage then gradually diminished, by 2009 covering 1453 km(2). This investigation employs the use of the Ice, Cloud, and land Elevation Satellite (ICESat) laser altimeter to derive freeboard of sea ice in McMurdo Sound from 2003 to 2009 and hence infer thickness changes over this time period. Two techniques for freeboard retrieval are compared. 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.