ANT-XXVI/3, Weekly Report No. 7

15 March - 21 March 2010

A different plan was supposed to define our work during the upcoming days. But Max, our meteorologist, came up with a weather report which allowed only a narrow time window for recovering the GPS instruments, and giving the geologists another chance for rock sampling, on the mainland. Therefore, we interrupted seismic profiling to head to the coast near the Pine Island Glacier.

The geodesists of the Dresden University of Technology conducted their first GPS measurements in the region of the Pine Island Bay four years ago. Three of those stations on bedrock are now being repeatedly observed. Comparing the measurements of the years 2006 and 2010, differences in the vertical and horizontal components will be yielded. Especially for the vertical component, a significant change is expected, reaching 1 to 2 cm for the time span of four years. The vertical motion is caused by the glacial-isostatic adjustment, which is the land uplift due to the ice masses having disappeared since the last glacial maximum. Moreover, the analyses is expected to show to what magnitude the ice mass losses of the last years and decades, especially in the region of the fast-flowing Pine Island Glacier, contributed to the present-day vertical deformation.

The program of our land geology team has been coming to an end. Having chosen their last sampling spot, they head for Clark Island, which is located more or less in the middle of Pine Island Bay. During the last weeks, the team has taken samples from 12 small, mostly unnamed islands, forming two 100 km long horizontal profiles in north-south and east-west direction across Pine Island Bay. Most of these islands have never been visited before and their geological structure is practically unknown. The team found that the islands of the eastern part of the Bay are mainly composed of granites whereas towards the west, rocks are metamorphosed and strongly deformed. Back in the labs, analyses of the samples will reveal the age and geodynamic evolution of these rocks, from the breakup of the supercontinent Gondwana to the younger rifting and deglaciation history of West Antarctica.

The oceanographers were also taking advantage of their last chances to complete their measurements on the properties of the ocean water in Pine Island Bay. On six hydrographic sections across the axis of the deep glacial trough, the warm and saline water of circumpolar origin can be traced from the deep basin over the shallow shelf areas to the tongues of the glaciers (small ice shelves). Being the densest water mass, it flows along the bottom deep into the cavity caverns of the ice shelf, thus becoming an important factor of glacial melt with its temperature of + 1.2°C (which is 4°C above the freezing point at the grounding line). A comparison with existing data of measurements years ago will allow an estimate of the changes in water temperature within the last 15 years, and show how they affect the mass balance of the Pine Island Glacier.

The oceanographers, however, were being denied a particular highlight. A helicopter-CTD station was supposed to be installed at a location opposite of a sea-ice tongue, which had been sitting for weeks between Pine Island Bay and the western Amundsen Sea Embayment. It was a good opportunity as the ship needed to be in a stable position for a few hours for a routine maintenance job to be completed in the engine compartment. This is usually done best by ramming the ship into solid sea-ice. But increasingly strong winds and the instable consistency of the sea-ice rendered the helicopter-CTD plan impossible.

Having used most of our last chances in Pine Island Bay, the ship’s track is now bringing us towards the open ocean of the Amundsen Sea for the last part of work in our exciting area of operation.

With best regards from all participants
Mirko Scheinert, Michael Schröder, Cornelia Spiegel and Karsten Gohl