An Autonomous Profiling EXplorer (APEX float) was deployed in the Southern Ocean (SO) on December 18, 2012 in the Drake Passage, between the tip of South America and the West Antaractica Peninsula (WAP), at 64.813 degrees West and 59.870 degrees South. APEX floats are capable of profiling the subsurface environment down to a depth of 2,000 m with a vertical sampling resolution on the order of 10 to 100 meters. Between ocean profiling, the float remains at a depth of roughly 1,000 meters, before diving to 2,000 m to begin the profiling mission. Once at the surface, data is transmitted via the ARGOS satellite system before float returns to depth and awaits the next profile.
As of March 2010 there have been over 6,000 APEX float deployments by institutes spanning 19 countries with the majority of float deployments occuring in tropical and temperate waters. The standard float configuration calls for a pumped CTD which measures temperature, pressure, and salinity. The MUSTACHE float is only one of two deployed in the SO that can also measure oxygen and chlorophyll concentrations, along with CDOM and total partical backscatter.
Primary production in the SO is physically-forced, iron limited system. Over the entire basin, production is limited for months at a time due to high seasonal variability in the available solar irradiance while mesoscale ocean processes (eddies) and atmospheric forcing (wind stress) may play a significant role in the presence and "patchiness" of chlorophyll blooms.
The goal of the MUSTACHE is to further quantify the role of higher-frequency physical-biological interactions in the SO. A better understanding of these processes could prove to be paramount in the understanding of problems ranging from air-sea gas fluxes to the geospatial distribution of foodwebs in our changing climate.
To capture the higher frequency variability in the SO, the float has been set to profile and surface every two days during the southern hemisphere summer months. The top figure to the right, shows the MUSTACHE float locations as of 4/29/12 plotted on Google Earth. The background shadding is the absolute dynamic topography from TOPEX on 4/24/12 via aviso.oceanobs.com. The dark blue shadding is roughly -100 cm while the yellow/green is roughly +100 cm. This demontrates that sampling every two days allows the float trajectory to roughly follow barotropic pressure gradients imposed by sea surface height anomalies (mesoscale eddies). In the SO cyclonically rotating eddies spin clockwise and are associated with anamolously low sea surface heights (the opposite for anti-cyclonically spinnning eddies).
The middle figure shows the temperature-salinity diagram for measurements to as of 04/24/12. The dashed contours show the density anamolies (from 1000 kg/m^3) with the vertical orientation of these contours indicating density is driven by salinity at low temperatures. The T-S diagram shows and interesting feature at a depth of about 100 m. A sharp decrease in temperature that is located at that depth. This cold water mass, potentially a residual signature from previous winters, has an impact on the upper ocean stability as its depth appears to relate to the depth of the mixed layer.
The bottom figure shows the percent O2 saturation through time and depth. This shows the upper 100 m remains well mixed and uniform above the black line, which is the depth of maximum stability. The blue line is the depth of maximum chlorophyll concentration.