Interannual variation of landfast ice condition in Lutzow-Holmbukta, Antarctica, derived from navigation log of icebreaker Shirase

Characteristics of sea-ice conditions in Lutzow-Holmbukta, Antarctica, have been investigated using the ice navigation log from the icebreaker Shirase, which has made a voyage almost at the same season and in the same sailing route every year since 1983. The vessel is considered as a suitable monitoring platform for sea ice. Not only basic information such as ice thickness and snow depth, but also ramming icebreaking data have been analyzed. In particular, the penetrating distances by ramming reflect difficulty in ice navigation and show distinctly interannual variations from 1983 to 2002. The periods with longer distances are consistent with those when breakup of landfast ice occurred frequently in the bay. The penetrating distances have shown a tendency to increase since the end of the 1990s, when ice breakup has been pronounced.