The role of the atmospheric circulation in very extensive summer sea ice in the Ross Sea, Antarctica in 2003

An important feature of Antarctic sea ice is that the Ross Sea is the only region where positive trends in ice extent are occurring in all seasons of the year. Since 1998 three austral summers (January and February) of remarkably extensive ice have occurred, the most notable being 2003 when the lowest amount of open water on record was found. Some studies have argued large icebergs in some of these summers disrupted the normal divergent northward sea ice drift that usually removes ice from the region. This paper examines how far anomalous atmospheric circulation patterns were responsible for these unusual events focussing on the most anomalous case in 2003.

The paper uses high quality ice concentration and ice motion fields derived from satellite data and wind data from the ERA-40 reanalyses to quantify the impact of the atmospheric circulation on the 2003 summer ice extent. Key findings are that widespread southward ice drift leading to extensive ice compaction preceded the development of positive ice extent anomalies in the 2002 spring, the areas of most anomalous ice motion coincided with the most anomalous atmospheric circulation, and very early new ice formation in the late summer was related to much reduced ocean thermal warming in late spring and summer caused by the persistence of the ice cover from the preceding spring. These results and a comparison to another summer of extensive ice without a large iceberg will be used to argue that the large iceberg was not the cause of the severe ice conditions but did worsen them.