Studies on sea ice and polynya off the Cape Darnley in East Antarctica, using the ALOS PALSAR and passive microwave data

Kay I. Ohshima(1) and Takeshi Tamura(1)

(1) Hokkaido University, Kita-19, Nishi-8, Kitaku, 060-0819, Sapporo, Japan


The Cape Darnley polynya, which is located west of the Amery Ice Shelf in East Antarctica, is a huge polynya whose size is more than 100 km x 100 km. According to our previous studies, this polynya has the second highest ice production in the Southern Ocean after the Ross Ice Shelf Polynya. The purpose of this study is to develop and validate the sea ice thickness algorithm from the combination of the ALOS PALSAR data and other satellite data, and to clarify the formation process of the polynya and its variability. Since a shallow bank with 50-200 m depths exists east of this polynya, icebergs drifting from the Amery Ice Shelf via the Antarctic Coastal Current are apt to be grounded on this bank. The PALSAR backscatter images can discriminate between icebergs, fast ice, first-year ice, and new ice around this area and clearly visualize the Langmuir circulation within the polynya. According to our analysis using several PALSAR images, the first-year ice is accumulated around the grounded icebergs, and then the iceberg tongue (fast ice) is formed from the coast (south) to offshore (north) for about 100 km length. The shape and location of this grounded iceberg tongue has not been changed at least for our analysis period of one year. Because a part of the westward Antarctic Coastal Current can pass through the tongue, sea ice is carried away in the west side of the tongue while accumulated in the east side of the tongue. This filtering effect of the tongue is considered to be very important on the polynya formation. Analyses of the surface wind data and the polynya areal extent derived from the microwave data also confirmed that the polynya formation cannot be explained solely by the dominant northwestward wind and that the coastal current is an important component for its formation. The array of current meters and conductivity-temperature recorders, which are now moored in this region by the Japanese IPY project, will further clarify the formation process of the polynya and the associated dense water formation. In our presentation, we will also discuss the relationship between the PALSAR backscatter data and thin ice thickness data derived from the microwave sea ice algorithm.


Symposium presentation


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