CA 11-12 XXVII Ita. Esp South Africa SANAE 51

Extract from the Italian XXVII Antarctc expedition report and NOAA AX25 Report

The Antarctic Campaign 2011-2012 has seen the fulfillment and continuation of the research activities of the Project SOChIC carried out in collaboration between the PNRA, and the South African National Antarctic Programme (SANAP).
Activities connected to the launch of Expendable Bathytermograph (XBT) probes have been carried on in the framework of The GoodHope and NOAA/AOML Atlantic high-density projects.
Both projects carry on an intensive monitoring programme that provide information of the vertical thermal structure of the surface layer of the Ocean.
During the 158th voyage of the R/V Agulhas between Cape Town and Antarctica a total of 280 XBT Have been deployed with a spatial resolution of about15 nautical mile (2 hours of navigation).
Most deployments reached a maximum working depth of the Sippican Deep Blue XBT, which is in the order of 780 m but slower ship speed allowed data collection up to 900 m depth.
XBTs were funded by the NOAA's Office of Global Programs as part of their High Density XBT project at NOAA/AOML.
During the first leg of the cruise, from Cape Town to Antarctica (Fig 1), 161 XBT were launched between -33.86°S/18.01°E (08/12/2011 h16:16) and -70.48°S/8.14°W (22/12/2011 h22:02) where sea ice condition imposed a stop of the deployment.
The release of 167 XBT probes (only 6 showed malfunctions) occurred along the route shown in Figure 1, with equivalent temporal resolution of about 2h, to the average speed of the ship, about 20 nm.

Fig 1 Map of XBT launches in the period 8-22/12/2011 (left), and section of temperature relative to the layer 0-900m, from Cape Town to Antarctica (right).

Is worth noting that the spatial and temporal resolution of the launches XBT is the result of a careful planning process aimed at optimizing the scientific and technological resources available to the research project. Indeed launches XBT were alternated with the use of a probe UCTD (Underway CTD) gathering, always moving ship, the data of temperature, salinity and pressure of the first 400 meters of the water column. The final result obtained through the merging of the two datasets is a spatial/temporal resolution in data collection of approximately 1h (10 nm).
The section of temperature obtained through the use of XBT probes has allowed to identify the location of the main thermohaline fronts of the Antarctic Circumpolar Current (ACC).
Furthermore during the crossing were released about 20 different types of float able to collect various data, including, in addition to temperature and salinity, dissolved oxygen and nutrient concentration.
Second leg of the cruise started on the 22/02/2012 and was concluded on the 02/03/2012. During this leg 119 XBT were launched between 69.22°S/7.11°W and 35.63°S/17.44°E.
Ship and weather troubles imposed a track different from the expected Goodhope line. Map of deployments is shown in figure 2 as well as temperature section from profiles.

Fig 2: Map of XBT launches in the period 22/02-03/03/2012 (left) and section of temperature relative to the layer 0-900m, from Antarctica to Cape Town (right).