Mr. Rigoberto Garcia, a CIMAS/UM employee working with AOML's Physical Oceanography Division, joined with partners from Argentina and Brazil on a recent cruise to study the Meridional Overturning Circulation (MOC) at 34.5?S in the South Atlantic during October 4-16, 2014. This cruise, onboard the Argentine research vessel ARA Puerto Deseado, was the ninth joint cruise in support of the NOAA-funded Southwest Atlantic MOC (“SAM”) project since the beginning of the project in March 2009. Participants in the cruise included researchers from the Universidade de Buenos Aires (UBA), the Servicio de Hidrografía Naval (SHN), the Instituto Nacional de Investigación y Desarrollo Pesquero (INIDEP), the Universidade Federal do Rio Grande (FURG), and the Universidade de Sao Paulo (USP), as well as NOAA-AOML.

The MOC is the major driver in the north-south redistribution of heat in the ocean-climate system. It is a vertical circulation cell that exchanges surface and deep waters via poleward surface transports, sinking at high latitudes, and upwelling elsewhere. MOC variability has been linked in numerical models to significant changes in precipitation patterns, surface air temperatures, and hurricane intensity over large portions of the Earth. NOAA-AOML is taking a leading role with its partners to collect observations of the South Atlantic portion of the global MOC system to gain a more complete understanding of its complex nature. A complete trans-basin array to measure the MOC at 34.5°S is in the process of being deployed, and the NOAA instruments near the western boundary are the cornerstone of the full array. On this Puerto Deseado cruise, the scientists acoustically downloaded data from four pressure-equipped inverted echo sounders (PIES) moorings in the SAM array, as well as two similar Brazilian instruments. These instruments send sound pulses to the sea surface and listen for the return of the reflected sound waves. The “round-trip acoustic travel time” measurements are then combined with historical hydrographic data to obtain daily estimates of the temperature, salinity and density for the full water column above the mooring. The pressure gauges meanwhile provide information on the variability of deep water flows. The combination of data sets from the PIES moorings provides long term observations of the shallow and deep western boundary currents at 34.5°S – key components in the MOC system. The existing array is scheduled to continue through at least 2016, with annual or semiannual cruises planned to collect new hydrographic information and to acoustically download PIES. NOAA's contribution to this effort is funded by the Climate Program Office/Climate Observations Division and the NOAA Atlantic Oceanographic and Meteorological Laboratory.

Science party photo from the October 4-16, 2014 cruise onboard the Argentine research vessel ARA Puerto Deseado.