Earth Institute News
Contact: Mary Tobin
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Reports From the Field
The Antarctic CORC/ARCHES Expedition
April 16 through May 10, 2004
Report Three -- May 1, 2004
Dr. Gerd Krahmann, of the Lamont-Doherty Earth
aboard the R/V L.M. Gould, Weddell Sea, Antarctica...
Afternoon, May 1, 2004
Latitude: 63S 6.5'
Longitude: 55W 8.6'
Wave height: 0.0m (in sea ice)
Air temperature: -5C (23F)
Wind Speed: 11kn (12mph)
A week ago, the other group on board (geologists under chief scientist Eugene Domack) took over the scientific responsibility. Their primary objective was to reach the area of the former Larsen ice shelf on the eastern side of the Antarctic Peninsula. This ice shelf (basically a massive glacier flowing into the ocean and covering a large area of the sea) broke up a few years ago and now, for the first time, allows ships to reach a region formerly covered by ice.As for our group, the late scheduling of our cruise (April-May here is late fall with rapid freezing of the open ocean) meant that Domack needed a lot of luck to encounter favorable ice conditions. Satellite images supplied by personnel at Palmer Station (western side of the Antarctic Peninsula, see our reports from last year) indicated that the direct route to the former ice shelf region was already blocked by ice. We thus tried two passages between islands. We quickly had to give up on the first passage as winds had pushed ice floes on top of each other, building ridges up to 10' thick. Our ship can handle, at most, 5' thick ridges and 1' continuous ice.
The second passage we tried, the Prince Gustav Channel, was covered by a mixture of newly formed ice and smaller ridges. We were able to proceed to a location close to the Larsen ice shelf—only to find that the mouth of the passage was blocked by large icebergs and very heavy ridges. After some scientific work in the deep part of the channel, we had to abandon our attempts to reach the Larsen ice shelf. Retracing our route through the Prince Gustav Channel, we headed southward towards another region of scientific interest.
During the night strong winds created new ridges in the ice and the ship was actually not able to move for several hours. The captain used a moment of weaker winds to break free and we headed north towards more open waters. Had the winds not calmed down a little, we would have run the danger of being stuck in the ice for the whole southern winter. Conditions on the following day worsened by the hour and peaked at wind speeds of 94kn (103mph). The air temperatures had dropped to less than -20C (-5F) and water from the increasing waves froze instantaneously on deck. This freezing of seawater on the superstructure of a ship is extremely dangerous as it can cause the ship to be so top heavy that it can capsize within a moment. The decks were closed for us scientists and only crewmembers were allowed outside to break away our several inch thick ice crust. Luckily the bad weather lasted for only a day and we proceeded to another region northeast of the Antarctic Peninsula.
We arrived there yesterday and have now begun geological work. After a first survey of the water depths, Domack's group had identified a number of deep locations in which sediments could accumulate. Today we did the first so-called Kasten core. The coring system consists of a square-diameter hollow steel tube that is lowered to the seafloor. Heavy weights on its top push this 3m (10') long tube deep into the mud. After it is sunk into the mud the tube is hauled back on board and taken into the labs. A side panel on the tube can be removed and allows the geologists to analyze the various layers of sediment. The chief scientist estimates the age of the deepest layers of the core at a few thousand years.