MEASUREMENTS OF ANTARCTIC SEA ICE THICKNESS DURING THE ICE TRANSIT OF S.A. AGULHAS Ⅱ

摘要

The South African polar supply icebreaker S.A. Agulhas Ⅱ was permanently instrumented for ice load measurements when built in Finland in 2012. The ship is used as a research platform during her annual relief voyages to Antarctica. The performance data is complemented with ice observations and ice thickness measurements using both electromagnetic (EM) method and stereocamera system. The thickness measurements are described and results from the first full campaign 2013-2014 are presented. The first period of ice transit extends from early December to early January while the latter covers late January and early February. Both include meridional transits between the ice margin and ice shelf, and zonal transits along the shelf. Six hour ice thickness averages grow gradually from 0.5 m of ice margin to 1 m at about 200 km from the shelf. This is followed by a transition to extremely deformed and 1.5-2 m thick near shelf ice types. The two types have different thickness distribution characteristics which is also reflected by the very large amount of ramming during the zonal transits. The EM results are in a good agreement with observations which also demonstrates that reliable thickness data can be obtained by careful observational methods. The reliability of shipborne thickness data to represent regional thickness variation is discussed and different ways to define the thickness distribution are compared.