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First Cruise in Three Years in Support of the South Atlantic Meridional Overturning Circulation Project

This story is excerpted below. Read the full story on NOAA’s Atlantic Oceanographic and Meterological Laboratory (AOML) website!

After two weeks at sea, the South Atlantic Meridional Overturning Circulation (SAM) project team, led by Renellys Perez and Shenfu Dong (NOAA/AOML), completed its first cruise since June 2019! 

The SAM project, which began in 2009, seeks to capture the daily variability of key components of the Meridional Overturning Circulation (MOC) in the under-sampled South Atlantic Ocean. The MOC plays a major role in redistributing heat, salt, dissolved oxygen, nutrients, and carbon throughout the global climate system. Variations of the MOC can have important societal impacts on coastal sea levels, marine heat waves, extreme weather events, and shifts in regional surface temperature and precipitation patterns.

The SAM project is funded by NOAA’s Global Ocean Monitoring and Observing Program and consists of an array of moorings along 34.5° S. The array includes four pressure-equipped inverted echo sounders (PIES) which collect pressure just above the sea floor and vertical acoustic travel time measurements (the time it takes for a sound pulse to travel from the PIES on the seafloor to the sea surface and back). The acoustic travel time measurements are used to generate profiles of temperature, salinity, and density near the western boundary along 34.5° S, off the eastern coast of Brazil. Data from these instruments are used to monitor the southward-flowing Brazil Current and the Deep Western Boundary Current as they carry components of the MOC along the western boundary of the basin. These moorings also collect bottom temperature data, and have been used to generate a 10-year time series of bottom temperature along 34.5° S.

The US, Argentina, and Brazil maintain the array through an informal collaborative agreement – each partner contributes to annual or semiannual fieldwork either with resources (ship-time and equipment) and/or personnel. Due to the pandemic, this was the first cruise for the SAM project since June 2019, meaning there have been no recoveries or deployments of moorings, and no acoustic data downloads for over three years. 

In spite of rough weather and ship engine difficulties, the cruise visited three of five mooring sites. Thankfully, the two NOAA/AOML moorings set to auto-release were successfully recovered (with all of the data!) and new units were deployed in their place to continue collecting these key time-series measurements. An additional Brazilian mooring was also recovered and redeployed.

In addition to servicing the PIES moorings, CTD-LADCP (Conductivity, Temperature, Depth – Lowered acoustic Doppler current profilers) casts, eXpendable BathyThermograph (XBTs) drops, and water sampling operations were conducted by the Brazilian oceanography Institute in the University of São Paulo and National Institute for Fisheries Research and Development (Argentina) student volunteers and personnel.

Many thanks to Ulises Rivero, Pedro Peña, and other members of the AOML instrumentation group who provided ground support during the cruise.