Sea Ice Thickness and Volume Derived from Ice Charts in the Southern Ocean during 1995-1998

Following the author's research focus of deriving sea ice thickness and volume based on ice type from weekly ice charts in the Ross Sea from 1995-1998, this presentation extends these analyses to the entire Southern Ocean. Ice thickness derived from ice charts is compared to Aspect ship-based estimates on the scale of individual ice chart polygons (tens of kilometers) and on a regional basis. Thickness variability on the scale of individual ice chart polygons is found to be compatible with WMO thickness ranges except in areas with high concentration of ridging in the Ross Sea. Reasonable agreement is also found for integrated results on the regional scale of the Ross Sea. Author's presentation will further the comparison over the full Southern Ocean. We extend the Ross Sea analyses of the weekly ice charts to assess the annual cycle and interannual changes in the sea ice extent, thickness and volume of the Southern Ocean during the four-year period. The seasonal minimum and maximum sea ice extent highlight interesting characteristics of the Southern Ocean sea ice. For example, the summer season shows the largest inter-annual variability in maximum sea ice extent which may indicate the importance of retaining multi-year ice through the summer melt period. Sea ice thickness distributions are computed by season and over the four-year period (climatology) at the regional scale. A number of features in this climatology follow trends uncovered by Worby et al. (2008). As an example, in the summer months of December, January and February (DJF), there is a period of extremes. The mean thickness values are the highest of all four seasons because the multi-year-thick ice remains in the summer, while very little thin ice is retained. The thin ice bin accounts for a very small percentage of the total ice. Moreover, in the winter months of June, July and August (JJA), redistribution of thin ice into thicker ice categories is apparent. An examination of ice thickness at the regional scale displays some trends, as for example, with the western Weddell Sea showing the least variability, with the main feature being the high percentage of thick ice year round. The full analyses of extent, thickness and volume will be displayed at the regional scale over the 4 year period.