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position map04/27/04

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Mary Tobin
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Reports from the Field

The Antarctic CORC/ARCHES Expedition, April 16 through May 10, 2004

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Second Report -- April 24, 2004

tim newberger
Tim Newberger is preparing a rope connecting two flotation devices of our mooring. The yellow instrument in the background are three plastic pieces protecting three hollow glass balls each. Each glass ball provides about 20 pounds of floatation to the mooring so that it stands upright in the water during the recording time and so that it refloats to the ocean's surface once a heavy anchor is dropped. Image credit: Gerd Krahmann
Dr. Gerd Krahmann, of the Lamont-Doherty Earth Observatory
aboard the R/V L.M. Gould, Weddell Sea, Antarctica...

Morning, April 24, 2004
Latitude: 60S 57.4
Longitude: 49W 20.5
Sky: dense fog
Wave height: 1.5m (5')
Air temperature: 0C (32F)
Wind Speed: 12kn (13mph)

The past three days of this cruise were devoted to our group. After reaching the South Orkney Islands on April 20th, we headed southeast towards our working area. We knew from satellite images that our route was ice-covered, but we didn't know if this ice was still navigable for our ship. At 5am, the captain woke me and asked me to come to bridge. The scenery was quite amazing. The horizon to the south of us (where we were headed) was cover by an unpenetrable mixture of sea ice from last year (very hard and thick), big icebergs, and newly formed sea ice (soft and less thick). It was obvious to us that we could not reach our planned positions via a direct route. We decided to proceed further eastward hoping to find a gap in the ice cover.

After several hours eastward, we reached a dead end with the same icy conditions. That was pretty much the end of our original plan. We had to turn northward to get out of the thickest ice. After some 30 nautical miles (about 35 miles) we turned again eastward to reach two positions we had occupied last year. It took us several hours to get there.

ice conditions
This picture gives an impression of the lighter ice conditions which we were still able to navigate. The big iceberg in the background is nearly 100 feet high above the sea surface and probably reaches some 500 feet deep at a length of about one mile. The steam-like fog you see is called sea smoke. It is formed at very cold air temperatures over open patches of water. But remember that the water temperature is very close to its freezing temperature at about 28F (-1.8C). The air temperatures were very cold with less than -4F (-20C) and a wind chill of -49F (-45C). Image credit: Gerd Krahmann

We did two CTD casts measuring temperature and salinity from the ocean's surface to the bottom. As there was no way to go south within our alloted time (only 3 days were dedicated to us) and without running into the danger of getting stuck in the ice, we finally cancelled the original plan and headed northeast, to a region where we had worked last year, after encountering similar ice conditions to the south.

But different from last year, the northeastern area was also covered by ice. Luckily, it was mostly young ice, and we able to break through at a very slow speed (about 3-4 miles per hour). All this slow movement cut heavily into our time, leaving only little for scientific work. After doing a CTD cast at the deepest spot of an undersea valley through which Weddell Sea bottom water (a very cold and dense water formed in the Weddell Sea) leaves the Weddell Sea, we deployed a mooring at the same location. This mooring will record temperature and salinities over the next one to two years, depending on when we will be able to recover it.

After the mooring deployment, we did another CTD cast on the other side of the undersea valley (which is only 20 miles wide) and then headed west to a very deep spot north of the South Orkney Islands. This spot is scientifically interesting to us because there the water flowing in through valley should cover the lowest 1500m. What we typically find there is, however, significantly warmer than the inflowing water. This means that strong mixing must take place between the inflowing cold Weddell Sea bottom water and overlying warmer water.

After this last CTD cast, we had used up all our alloted time, and the other group on board took over.

At the moment we are steaming west towards their working area which we likely will reach tomorrow afternoon. It is interesting to note that at the moment we are still seeing intermittent patches of ice in an area which typically is ice free this time of the year.

Our chief scientist is maintaining a close to-real-time web page back at his home institution (Hamilton College). If you are interested in more information go to http://www.hamilton.edu/news/exp/Antarctica/2004/

 

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