Fostering collaboration between North and South Atlantic mooring array teams

By Kyle Cooper, SAEON Intern Tweet

The Collaboration of Overturning-Circulation Observing Arrays (COCOA) in the Atlantic Ocean was held at the National Oceanographic Centre, Southampton (UK), in July 2015.

The aim of the workshop was to foster collaboration between the South Atlantic Meridional Overturning Circulation (SAMOC), and particularly the South Atlantic Mooring Buoy Array (SAMBA - located at 34.5^oS), the North Atlantic Meridional Overturning Circulation and the RAPID mooring array (located at 26^oN) on scientific and technical levels.

The North and South Atlantic Meridional Overturning Circulation is part of the global overturning circulation (Fig. 1), which is a long-term moderator of the earth’s climate. The global overturning circulation is driven by the different density gradients from the variations in salinity and temperature and takes around 1 000 years to fully circulate the global oceans.

Figure 1: A schematic of the global overturning circulation. The circulation is driven by changes in the density of the ocean due to flux of salt and heat. The Atlantic falls in a key location with a number of glaciers adding freshwater and the Mediterranean adding salt

Atlantic Ocean - an area of high interest

The Atlantic Ocean is an area of high interest due to the changes in salinity caused by freshwater input from the melting of Greenland, its surrounding glaciers and the sheet ice in Antarctica.

The arrays (moorings holding instrumentation that are deployed along a mooring line) monitoring the Atlantic MOC are extensive as they extend across the Atlantic Basin having a large amount of instrumentation. These instruments need to be calibrated and then prepared into a product that can be understood and scrutinised.

The RAPID Array at 26^o N was first deployed in 2005 and is still operational. The SAMBA array is still in its infancy compared to the RAPID array and was deployed in 2014 at 34.5^o S.

Exchange of knowledge and expertise

The COCOA workshop allowed for the detailed exchange of knowledge, expertise, technology and techniques from the North Atlantic teams over to the South Atlantic teams that maintain and process the mooring arrays. This will ensure that the methods for calculating the heat and mass transport between different arrays (SAMBA and RAPID) are consistent.

Due to the infancy of the SAMBA array, a large portion of the exchange occurred on the technical level. The different mooring designs were discussed extensively - such as the Acoustic Doppler Current Profilers (ADCPs) used to measure current speed and direction, ballast anchors, acoustic releases, wire rope and MicroCAT sensors used to measure temperature and salinity.

The database structure and hierarchy is well established within the RAPID team and plays a key role in the data processing, which is performed in stages (0 - 4). The MicroCAT calibration (stage 3) was extensively discussed.

The South Atlantic teams have not used MicroCATs before, and the workshop ensured a successful exchange of knowledge and expertise on the calibration process. As SAMBA was still at a technical processing level, the scientific outputs are still to come and positive interactions ensured that the South Atlantic teams were briefed on possible problems they might encounter.

Overall the workshop was a success, with the RAPID team freely sharing their experience and expertise with the SAMBA team. As the SAMBA project progresses, this collaboration will continue.

The expertise gained through this collaboration will be used for the ASCA programme, particularly with regard to calibration of MicroCATs and generation of products. The workshop has played a key role in advancing the technical and processing abilities for the current mooring array programmes.

The 2015 COCOA workshop brought together scientists and technical personnel from Argentina, Brazil, South Africa, the United Kingdom and the United States. Photo courtesy of Ben Moat, NOC