Research Objectives:
The distance between Antarctica and South America is relatively narrow at the Drake Passage. Here the Antarctic Circumpolar Current which drives the waters in the Southern Ocean is extremely strong. This project measures the seasonal to interannual variability of upper ocean temperature and geostrophic transport through Drake Passage. The project has been ongoing since 1996 during which researchers have observed substantial variability in circulation, transport and water properties on time scales from seasonal to interannual, and spatial scales from mesoscale eddies to the Antarctic Circumpolar Current cores.
Closely spaced measurements are collected underway on six to eight crossings per year. Measurements are taken by two kinds of probes that are deployed and send data back to the vessel via radiotelemetry: XBT (eXpendable BathyThermographs recording temperature) and XCTD (eXpendable Conductivity Temperature Depth sensors recording salinity). The XBTs are loaded and launched using an automatic launcher and associated software that automates the collection of the XBT profiles. The system drops an XBT probe at pre-specified locations and prompted by the GPS location. Approximately 70 XBTs are dropped per crossing.
On sampling cruises XCTDs are dropped every half degree of latitude between 55 and 60 degrees south. Salinity bottle samples are also collected at each XCTD deployment. This bottle data will be used to calibrate the XCTD and underway thermosalinograph (TSG) data. Offsets between the bottle salt data and the TSG can be significant, and this is one way of determining the offset. Onboard technicians support the project by setting up and loading the automatic XBT launcher, conducting the XCTD deployments, collecting the salinity bottle samples, and logging all project activities. Project data and logs as well as standard shipboard underway data (TSG, meteorological and navigation data) are sent to the principal investigator at the end of every cruise.
The information gathered is stored and in a high-quality database accessible on the Internet. These and other researchers study the magnitude and depth of penetration of the seasonal signals, the connections to atmospheric forcing, and the effects of interannual variations such as those associated with the Antarctic Circumpolar Wave. Data analysis is carried out in cooperation with the Argentine Antarctic Institute in Buenos Aires.
