The SBE 61 CTD: Measuring the Bottom Half of the Oocean

The Argo program, a global array of robotic profiling floats, measures the hydrographic properties of the upper ocean. But the current fleet only profiles to 2000 m, whereas the mean depth of the ocean is ~3800 meters leaving a large volume of ocean unexplored. Deep Argo is the expansion of this wildly successful program, pairing new float and sensor technology to reach the deep ocean. In conjunction with scientists and float manufacturers, Sea-Bird Scientific has developed the SBE 61 Deep Argo CTD for this purpose. Designed to profile from the surface to 6000 m, the SBE 61 rivals the accuracy of shipboard CTDs (±0.0002 S/m, ±0.001 ºC, ±4.5 dbar), but is shrunk to the size of a moored CTD. The ~60 instruments that have already been deployed are providing an unprecedented data set, giving long-term measurements of temperature and salinity in some of the deepest parts of the ocean. We will discuss these instruments, the data and where Deep Argo is going.