ANT-XXVI/3, Weekly Report No. 4
The geothermal heat-flow lance with its temperature sensors is prepared to be deployed at the sea-floor. (photo: M. Romsdorf)
22 February - 28 February 2010
A week full of events began relatively monotonous. After leaving Wrigley Gulf, we continued the seismic profile along the continental rise to the Amundsen Sea that we started a few days ago. With more than 1500 km in length, it is the longest continuous seismic profile in Antarctica and connects the well-surveyed Ross Sea with existing profiles in the Amundsen Sea. For the first time, it is possible to correlate sedimentary layers of these two large sediment deposition regimes of West Antarctica for the time before early glaciations to the youngest geological past. The seismic streamer and its recorders have been working steadily throughout day and night. The sea-ice situation appears to be quite promising at the entrance of the Amundsen Sea Embayment. The satellite images excite the scientists at the time anyway, because the sea-ice cover in the Pacific part of West Antarctica is at an exceptional minimum this year, which makes many areas accessible for the first time. But only a few hours after changing course large ice-floes were drifting towards the ship, driven by strong south-easterly winds. The streamer had to now be hastily winched back to the ship’s deck to prevent this expensive 3 km long cable and its depth-controlling ‘birds’ from being caught, damaged or even torn. We replaced it with an older and shorter streamer, which still records decent quality data. This replacement action was repeated several times because satellite images of ice cover often lack accuracy.
After the sea-ice event, the next unpleasant surprise happened: Our geomagnetic sensor, which is towed from the helicopter with a 20 m long cable, broke apart during a landing operation on deck. Was this the end of our helicopter-magnetic survey flights, at a time when we had perfect flight weather conditions and wanted to fill an important gap in a survey area we began surveying in 2006? With amazing skill and under high timing pressure, the crew and the Helimag team rebuilt the sensor. Geomagnetic surveying of the Amundsen Sea Embayment could now continue… The collected data are used to provide information on the tectonic basement structures beneath the shelf sediments. For instance, erosion takes place usually faster along tectonic faults compared to unfractured areas, and forms a relief which controls the flow direction of water and ice for a long period of time.
The so-called Heli-CTD was carried to a large ice-floe by helicopter to be deployed for measuring water temperature and salinity from surface to sea-floor. (photo: M. Schröder)
A very happy group of oceanographers landed on the helicopter deck. They successfully tested a new instrument to measure the water temperature and salinity in different water-depths from an ice floe. This so-called Heli-CTD can be transported to ice-floes by a helicopter and has the advantage that CTD profiles can be measured even where the ship cannot go or if the ship is busy collecting other measurements. Just as in Wrigley Gulf, the question addressed here is where the warm circumpolar deep water reaches the continental shelf and flows farther to the glaciers.
‚Polarstern, Polarstern, this is the Oden‘. Suddenly, a radio call burst through the calm early morning hour on the bridge. The Swedish research ice-breaker Oden was only a few miles away from us. On board were American and Swedish scientists working on geological investigations which were complementary to ours. We knew each other and used this opportunity to invite a team over to Polarstern, using one of our helicopters. Maps and information changed hands, the Polarstern was being toured. After only one hour, our guests had to leave again and return to the Oden. Such a ship-to-ship visit is such a rare event in this remote and lonely region of Antarctica that we will remember it for a long time.
We are now at the ice-shelf edge of the mighty Pine Island Glacier. This glacier or ice-stream, in union with its neighbouring Thwaites Glacier and their drainage area, has the potential of causing the sea-level to rise by 1.5 m if completely melted. Will the weather improve so that the geologists and geodesists are able to fly to their land sites?
The story will continue next week …
With best regards from all participants
Karsten Gohl