6 September, 1996 from Chief Scientist Bob Anderson
Dear Colleague, Greetings from the N. B. Palmer at 64 S, the southern terminus of the US.JGOFS Antarctic Environment and Southern Ocean Process Study (AESOPS) Site Survey cruise. This survey of the Antarctic Polar Frontal Zone represents the first of 11 cruises that will take place through the 1.5-year duration of the AESOPS field program. The principal objective of the cruise is a bathymetric survey using the Palmer's SeaBeam multi-beam swath mapping system to select specific sites for deployment of JGOFS time-series sediment trap moorings in November, 1996, along a transect at 170 W, at nominal latitudes of 51 S, 57 S, 61 S and 64 S. In addition, an expanded survey will be undertaken between 60 S and 62 S where upward of a dozen bio-optical & current-meter moorings will be deployed in October, 1997. Beyond the primary objective, this cruise offers the opportunity for several AESOPS PIs to collect samples of water, particulate matter, and zooplankton under winter conditions, as well as a first look at the composition of sediments in the region. In preparation for the first AESOPS Process-Study cruise, to take place in the Ross Sea next month, AESOPS investigators are using this opportunity to set up and test new CTD-rosette systems (both standard rosette and a new trace-metal-clean rosette), and to make ready instrumentation that will be used to measure CO2 system parameters and nutrients throughout the AESOPS cruises aboard the Palmer. All together, on-board analyses and sample collection during the Site Survey cruise include: dual underway PCO2 systems and a single underway TCO2 system; underway surface nitrate, nitrite and silicate; standard hydrocasts for nutrients, oxygen and salinity; sampling for del C-13 of TCO2; sampling for del N-15 of nitrate and of particulate organic matter (POM); sampling POM for organic biomarkers; sampling for naturally-occurring radionuclides; studies of the abundance, distribution and respiration rates of zooplankton; and the collection of surface sediments for a suite of organic, inorganic and radiochemical analyses. Three WOCE-type drifters were deployed successfully in the Polar Front region around 60 S. The cruise got off to a slow start. First, our departure was delayed by a day for extra time required to make ready for sailing. Then, heavy weather immediately out of port slowed the ship's speed to below 5 kts. By the second day of the cruise it was evident that we would have insufficient time to achieve all of our objectives at each of the survey sites. Consequently, a decision was made to abandon the site at 51 S to concentrate on the southern sites, lying over the crest and northern flank of the mid-ocean ridge, where rough bottom topography afforded higher priority for mapping with the multi-beam system. Well before reaching the southern-most site at 64 S, however, we began feeling like we are in a "you're damned if you do and you lose if you don't" situation. From published maps of ice distributions, we anticipated the maximum northward extent of sea ice to lie between 64 and 65 S. Needless to say, we were startled to encounter the ice edge at about 61.5 S. Air temperatures have dropped to at least -15C, though that is warm and balmy compared to conditions that will be encountered by participants in the Process-I cruise next month. The site at 64 S is under fairly complete ice cover (as I write this I can see no leads to the horizon, and scattered tabular ice bergs). The ice both slows the progress of the survey, and greatly deteriorates the quality of the multibeam data. We will spend about a day longer at the 64 S site, before moving north to complete the larger survey between 60 and 62 S. The Site Survey cruise represents what I believe to be the first collaboration, albeit informal, between JGOFS and RIDGE, two of the principal US Global Change Research Programs. Chris Keeley, RIDGE Program Coordinator, is aboard the cruise to help process SeaBeam data. Furthermore, he brought with him data from the RIDGE data base that will be merged with the data collected during our cruise. We hope that the data we collect, for the purpose of locating mooring sites, will be equally useful for the study of ridge processes in this region. JGOFS investigators will find the Palmer a delightful ship to work aboard. Captain Borkowski, the ship's crew, and ASA personnel have all provided fantastic support for our science efforts. Investigators making long transits to the Ross Sea can enjoy the sauna and weight room. Those who enjoy a little spicy Cajun cooking will find it easy to gain weight aboard this ship. Signing off for now, Bob Anderson Chief Scientist