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Earth Institute News

posted 03/11/03

Contact: Mary Tobin
845-365-8607 or

Reports From the Field

The Antarctic AnSlope Expedition
February 25 through April 11, 2003

AnSlope Cruise 1, Week 2
Tuesday, March 11, 2003, from Arnold L. Gordon, Chief Scientist
Aboard the R/V NATHANIEL B. PALMER, Ross Sea, Antarctica...

pink sunlight

A view from the Nathaniel B. Palmer

We have now set out all of the AnSlope moorings along the steep continental slope of the western Ross Sea. Quite a challenge amidst the nearly full cover of sea ice. The very capable group of ship handlers and mooring experts aboard the research icebreaker Nathaniel B. Palmer are congratulated on their fine job. The moorings consist of a weight (railroad wheels) and glass floats which hold up, nearly vertically a cable to which we attach instruments that measure temperature, salinity and ocean currents. The shallowest floats are around 300 m below the sea surface so as not be decapitated by drifting icebergs whose draft may reach that depth. The moorings remain in the ocean for one year, after which we recover them (there is a release near the bottom weight that we hope responds to our "let go" signal) and download the data.

The Ross Sea, as do other areas around Antarctica's coast, forms very cold dense water, which descends into the deep ocean to the north, spreading and chilling the lower 2 km of the world ocean. The resident deep and bottom water diluted by mixing with more buoyant water is lifted up towards the sea surface by the newly formed Antarctic bottom water. Some think that this process will slow or even stop with global warming, impacting on the future ability of the ocean to response to greenhouse induced climate change, but we really don't know. To develop the quantitative insight of how the process will response to a changing climate we must accurately gauge the governing forces that control the rate and properties of the descending cold-water plumes. Once we have the physics right, we have a hope of properly simulating this process in climate models.

In addition to deploying the AnSlope moorings we are lowering instruments to measure the ocean stratification (temperature, salinity, oxygen and various chemical tracers), currents and turbulence from the sea surface to the sea floor. In the western continental slope of the Ross Sea we discovered a stronger than expected outflow of cold saline bottom water. A descending plume of salty shelf water was observed with speeds of 100 cm/s (that's really fast).

on deck of the ship

Despite almost full cover of sea ice, ship handlers and mooring experts have successfully set out all of the AnSlope moorings along the steep continental slope of the western Ross Sea. The moorings remain in the ocean for one year, after which they are recovered to download the data.

Even in today's highly technical world, field oceanography offers an individual the opportunity to sense the spirit of exploration, to venture into the remote areas of the Earth, to reach into the unknown and uncover the truths of how the ocean "works." It's an adventure that too few experience. All of this is on top of the spectacular Antarctic views of the surrounding sea ice, icebergs and abundant sea life (penguins, seals, whales). A sense of comradeship develops aboard the ship as we all bring our individual strengths to the group.

We are now heading east to see how the plumes behave in regions where environmental conditions are slightly different from those in the west. We just crossed the international dateline, but did not change the clocks as we will cross back to the eastern hemisphere in about a week. The cruise, which began on 25 February in McMurdo Sound, Antarctica, ends in New Zealand on 11 April.

AnSlope is a program that is funded by the National Science Foundation. Besides involving a number of researchers from Columbia University's Lamont-Doherty Earth Observatory [myself, Martin Visbeck, Stan Jacobs, Peter Schlosser, William Smethie] it also includes scientists from Oregon State University, Texas A&M and the Earth and Space Research group in Seattle, WA. We have on board representatives from Germany and Italy that have collaborative programs with AnSlope.