Intense Anticyclones and Near Inertial Trapped Waves at the Global Argentine Basin Array of the Ocean Observatory Initiative

We analyzed physical oceanic parameters gathered by a mooring array at mesoscale spatial sampling deployed in Argentine Basin within the Ocean Observatory Initiative, a National Science Foundation Major Research Facility. The array was maintained at 42°S 42°W, a historically sparsely sampled region with small ocean variability, during 34 months from March 2015 to January 2018. The data documented four anticyclonic extreme structures events in 2016 and the presence of near-inertial waves (NIWs) trapped at depth within the anticyclones. Although the four anticyclonic structures had different characteristics (size, vertical extension, origin, lifetime, Rossby Number) they all featured low Richardson values well below the mixed layer associated to NIWs. Low Richardson values suggest favorable conditions for mixing. The anticyclonic features act as mixing structures at the pycnocline bringing heat and salt from the South Atlantic Central Water to the Antarctic Intermediate Waters. The extreme events were unique in the 29-year-long satellite altimetry record at the mooring site. However, the Argentine Basin is populated with many anticyclones and mixing associated to trapped NIWs probably plays an important role in setting up the upper water masses characteristics in the Basin.