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Earth Institute News

posted 03/31/03

Contact: Mary Tobin
845-365-8607 or mtobin@ldeo.columbia.edu

Reports From the Field

The Antarctic AnSlope Expedition
February 25 through April 11, 2003

AnSlope Cruise 1, Week 5
Monday, March 31, 2003, from Arnold L. Gordon, Chief Scientist
Aboard the R/V NATHANIEL B. PALMER, Ross Sea, Antarctica...

The picture shows the CTD package about to be launched into the ocean. The CTD package consists of many instruments attached to a frame, which is lowered by a winch to the sea floor, on a conducting cable. Signals are sent through the cable and recorded on thed ship's computer and displayed on the computer screen. The CTD package measures many things: 1. The CTD measures temperature, salinity, pressure [depth], oxygen; 2. two lowered Acoustical Doppler Current Profiler (LADCP) one looking up, one looking down each measures the currents within a range of 100 to 150 m of the package, providing a profile of currents as they descend and ascend; 3. A microstructure probe, which measures fluctuations in temperature and salinity at the centimeter scale, enabling estimation of ocean turbulence; 4, there are water samples, 24 in all, which descend in the open position, but can be closed upon command from the ship, to trap water from varied ocean depths. These water samples are used to determine salinity and oxygen for calibration of the CTD sensors, and various chemical tracers, as CFC, tritium/Helium and stable oxygen isotopes, which are used to tell us about the time scale of circulation and mixing within the ocean.

Still in an endless land of white. With sea ice reaching to the horizon all around us as it has for the last month, we can conclude that the whole world must be this way. But we know the ice protects us from the waves of the ocean to the north. We must cross that ocean before we reach civilization. The weather maps indicate hardly a break in the strong westerly winds of the circumpolar belt; the waves will be there, but of course we hope during the 6-day passage the winds will abate. We will be working in the ice until 3 April, and then we turn north into the waves. We must tie down (secure) all of the loose things that have accumulated as we crunched the ice cover. But as we hit the first big waves, I'm sure to hear crashing someplace on the ship. Other than that, the ship becomes quiet, as many people will not be seen, and the mess hall will be less crowded.

As I mentioned last week two of the AnSlope moorings were recovered after 3 weeks of data recording to re-position them.  This was a difficult task in the ice cover, but the re-deployment on 25 March when surprisingly smoothly.  The three-week records were attacked with vigor, providing us with a first glimpse of what we may find one year hence.  As an indication that we are on the right track, one mooring recorded a 6-hour burst of saline bottom water (sea floor near 1400 m) on 12 March at speeds of 130 cm/s, nearly a straight downhill run Drygalski Trough.  Relating such shelf water outbursts to movement of the front and tidal activity with the full year's time series is a key AnSlope objective.

The data collection phase of an oceanographic expedition is just one of the many phases of a scientific program. It is followed by a lengthy period of data analysis and publication of results, during which time there are workshops to compare data and ideas. Finally, publication of results follows data collection by 2 to even 5 years. However, the real start program is marked by preparation of the proposal to a funding agency, generally an agency of the federal government.  The AnSlope program is funded by the National Science Foundation's Office of Polar Programs.   The proposal took many months to prepare. We learnt a lot about the subject as we discussed what needed to be done to advance our understanding of this part of the climate system (ocean overturning along the margins of Antarctica) and design an efficient experimental plan that our peer reviewers will endorse.  But sadly the proposal was not funded on its first submission in June 2000. The second time (June 2001), AnSlope was funded. This is par for the course, with a 20-30% success rate; often a proposal does not meet with success until 3 to 5 tries. Of course, competition for funds is healthy, it sharpens the mind, but a low success rate leads to discouragement, and good science may remain unfunded, for varied reasons.

Once funded AnSlope entered the preparation phase, shipping all of our 'stuff' to the ship, and selecting the people who will participate on the cruise.  Cruise participants must pass a fairly vigorous medical and dental exam to qualify for work aboard a ship in a remote setting, far from medical facilities. This will be repeated for the AnSlope second and third cruises (the moorings are recovered during the third cruise in March 2004).

Back to AnSlope 1: After a friendly "see ya next year" to the moorings, we measured the ocean stratification and circulation with the CTD package (see the accompanying photograph) along the western mooring line, and continued that line to the north and west enroute to the trough that runs between the Balleny Islands and Antarctica. There is not very much data in this passage within which the Ross Sea saline bottom water flows towards the west. We plan to extend our observations westward along the base of the continental slope to at least 157E, before heading back to New Zealand.

We are still in ice [at 3:30 AM local time, 31 March, 68 deg 48'S; 167deg27'E] nearly 100%, though it has thinned to less than a meter, and is fairly uniform.  We can already feel the swell coming from the open ocean to the north. The satellite images indicate the Balleny trough is ice covered, so we anticipate to finally be free of ice once we head northward at the end of the science program, into the circumpolar wind and waves.

While we have encountered tough ice conditions during the cruise, the mooring and CTD array has not been compromised.  We have achieved the primary data collection objectives of AnSlope cruise #1. The heavy ice conditions resulted in higher fuel consumption than expected which will require cruise termination at Port Lyttelton before the scheduled 11 April ETA. How early depends on conditions encountered in the coming days.

As I mentioned in my previous reports from the field, our success under difficult ice conditions has been made possible by the remarkable abilities and experience of the ship officers and crew, of the Raytheon support team, and of the science staff. Its good to see such competent people at work, particularly as part of our minds are so concerned with the discouraging world current events.  My congratulations to all!