18 March 2007
Our oceanography program forms a large part of our daily scientific activities. A key objective for this work is to characterize the different water masses circulating in the Central Arctic Basin. By way of CTD (conductivity – temperature – depth) soundings and water sampling throughout the water column we can observe the location and seasonal evolution of these water masses that are defined by differences in temperature and salinity.
Like a pot of water heating on a stove, ocean currents are also driven by processes of convection (due to variations in temperature and density). Water that is cold and dense descends to the depths of the ocean while warmer water masses rise to the surface, creating currents that circulate throughout the world’s oceans, a process called thermohaline circulation. While this is a very simplified explanation of the processes involved, the displacement of these different water masses in the oceans is a key factor regulating global energy fluxes and climate. For example, the relatively warm Gulf Stream transports heat from low latitudes to the North Atlantic and Europe.
On board Tara we have a large sounding winch in the aft hold capable of lowering instruments to a depth of 3500m. With one person driving the winch inside and an ‘iceman’ outside controlling the instrument deployment and recovery, we lower the CTD at a speed of 1m/s, sampling every half second. Each CTD sounding takes between 40 minutes and 2 hours depending on the depth. After completion, data is downloaded at sent via satellite phone to the lab in France for analysis.