2002-2003 Science Planning Summary

Oceans & Climate

Dr. Bernhard Lettau
Program Manager

OO-260-O

NSF/OPP 00-03618
Station: RV Laurence M Gould
RPSC POC: Paul Olsgaard
Research Site(s): Science of opportunity on cruises

Drake Passage XBT Program
Dr. Janet Sprintall
Scripps Institution of Oceanography
Physical Oceanography Research Division
jsprintall@ucsd.edu
http://www-hrx.ucsd.edu/ax22.html

Deploying Team Members: Justine Afghan . Glenn S Pezzoli
Research Objectives: The Antarctic Circumpolar Current (ACC) is a powerful force that drives waters in the Southern Ocean - four times as fast as the Gulf Stream, for example. The current is even stronger wherever the distance between Antarctica and neighboring land is narrowed. These are the so-called chokepoints, such as The Drake Passage off the tip of South America and the sea regions between Antarctica and both the Cape of Good Hope and Tasmania. To determine the fluctuations in the transport of the ACC, scientists deploy bottom pressure gauges and similar instruments. This data can then be ranged against currents in the subtropical and subpolar gyres, and viewed in the context of the wind field over the southern oceans. Since 1996, scientists in this research project have been collecting data to characterize the water mass variability in the Drake Passage, to describe temperature and circulation variability in the Southern Ocean, and to define the role of the Southern Ocean in the global climate system.

Using high-density expendable bathythermographs (XBT) launched from the R/V Laurence M. Gould, researchers measure current, temperature, and depth for seasonal and year-to-year temperature fluctuations in the upper ocean within the Drake Passage. Since the water changes more rapidly there, they will conduct frequent casts across the Subantarctic, Polar, and ACC fronts.


Field Season Overview:
This "science of opportunity" takes advantage of the numerous Drake Passage crossings of the R/V Laurence M. Gould during logistics cruises to Palmer Station and science cruises to the Antarctic Peninsula. Using an autolauncher mounted on the stern, shipboard technicians deploy XBTs (expendable bathythermographs) and XCTDs (expendable conductivity-temperature-depth probes) on select crossings as weather conditions allow. The Sippican MK-12 and MK-21 Oceanographic Data Acquisition system records the data, which is sent by FTP over the internet to the principal investigator for analysis and processing.

About 60 casts per crossing are made from the 200-meter bathymetric contour off Isla de la Estados (in Argentine territorial waters) to the 200-meter contour off Antarctica.