May 17 pm, 2000

Katabatic Winds



Nat's senior thesis involved analysis of data collected in the area of Palmer Station on the west side of the Palmer Peninsula. Allison will be working on a project with Dr. Eugene Domack using satellite imagery to track Antarctic ice development and movement.

The Weddell Sea weather is stranger than any place I've ever been. The warm temperatures of this morning continued until around 10 am when a wind began to build. By noon the wind was blowing a constant 60 knots and had frequent gusts to the mid 80's. These are katabatic winds. They develop when the cold dense air over the glaciers is no longer held in check by the air over the ocean, which had become quite warm over the past 12 hours and therefore less dense. Descending from the plateau along the various glacial valleys they roared out onto the sea. The winds have driven the pack ice offshore along the southwestern part of the study area, leaving us with open water to work in. Without the damping influence of the ice though waves built rapidly in the open water and made work on the back deck impossible.

After mapping the sea floor under the open water area we have returned to the pack ice and are establishing a station to collect additional water, sediment and biological samples. Sample collecting in 900 meters of water is a long process. The instruments are lowered at around 60 meters per minute and then allowed to stabilize for 5 minutes or so 30 meters off the sea floor. Then, depending on the type of sampler, they are lowered at various rates the final thirty meters. Return to the ship is usually between 40-60 meters per minute. So in 900 meters of water a round trip at 60 meters per minute takes a half-hour not counting the time the instrument spends stabilizing on the surface and at depth. Additional time is needed to set up the sampling devices and unload them when they return to the surface. With a standard suite of 5 different sampling devices used each station is occupied for a long time.

Once the samples are back on deck they are handled in variety of ways. Grab samples are divided between the geologist and biologists and each then takes numerous sub samples depending on their needs. Core sediments receive the most involved treatment, with written descriptions of their appearance, incremental photography, and multiple sub sampling usually at 2 CM intervals for the length of the core which with a good recovery is 3 meters long. Finally when all samples are collected there is the clean up.

Dave Tewksbury
tewksbda@nbp.polar.org

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