ANT-XXVI/3, Weekly Report No. 3
Geologists at rock sampling work on Shepard Island. The helicopter in the background is waiting. (photo: C. Spiegel)
15 February - 21 February 2010
The excitement is building up.... Having changed course southward, Polarstern is making its way across the pack-ice toward Wrigley Gulf off the coast of Marie Byrd Land. The sea-ice conditions this year are favourable for the West Antarctic continental margin. We do not want to miss the opportunity to enter the coastal polynya – the ice-free strip just off the coast – to survey and investigate this relatively unexplored region for about 3 days. A group of geologists of the University of Bremen and the British Antarctic Survey as well as a team of geodesists of the TU Dresden have been staying close to the meteorologists for weather information. Their destinations are located in the region of the so-called Hobbs Coast, where the geodesists plan to install a GPS instrument so measure any tidal movement of the inner Gletz Glacier. If their measurement reveals such a movement, it would indicate that near-bottom sea-water reaches deep into the coastal area underneath the glacier. The first helicopter took off with the geodesists. The second one followed soon, carrying the geologists to a mountain chain in order to collect granitic rocks. But after only one hour of rock sampling, the team had to return to the ship as the weather changed rapidly for the worst. In the meantime, the geodesists had their GPS gear installed and returned to the ship. Happily, the geologists displayed their rock samples and now hope for another flight during the next couple of days.
The West Antarctic ice-sheet is of particular importance for the research teams which try to investigate the relationship between ice-sheet dynamics, climate and sea-level change. Most of the topography of this part of the Antarctic continent developed as a result of a rift process, similar to that of the East African Rift. Most of the present West Antarctic ice-sheet, therefore, sits on bedrock below sea-level, unlike its counterpart in East Antarctica. Climate computer simulations and analyses of sediment samples of the very few drill holes in the Southern Ocean and the Ross Sea suggest that the ice-sheet reacts sensitively to climate change. How has the bedrock topography changed along with the ice-sheet development? For instance, Marie Byrd Land is a region in which the Earth’s crust had risen several kilometres, caused by a hot zone in the Earth’s mantle. Is this uplift still ongoing today? The geologists of Bremen will try to reconstruct this crustal uplift of the so-called Marie Byrd Land dome. Rocks from the mountain chains of the Wrigley Gulf coastal region are very suitable for this study. But the weather forecast doesn’t look great …
Multi-beam echosounding data are mapped and reveal highly interesting features of the sea-floor. (photo: K. Gohl)
In the meantime, the working groups on board have been quite active and collected water samples, measured temperature and salinity of the sea-water in various water-depths, shot seismic profiles, and surveyed the sea-floor of the continental shelf with the multi-beam echosounder of Polarstern. Deeply incised troughs cut through the inner shelf off the mouth of the Getz Glacier, caused by advancing ice-streams of past ice ages. The temperature of the near-bottom water is a warmer than expected. How does the water find its way from the deep sea across the shelf break into these troughs?
The pack-ice is in our favour, but how will the weather develop? The outlier of a low pressure system north of us has been carrying humid air from the east, worsening the visibility. A short-lived weather window enabled us to conduct a flight to the nearby Shepard Island to collect additional rock samples. But the attempt to retrieve the GPS instrument from the site at the Gletz Glacier further up had to be abandoned a few miles before the station. However, there is always a plan B …
With best regards from all participants
Karsten Gohl