Executive Summary

South Atlantic Meridional Overturning Circulation (SAMOC) - Third Workshop

Silvia L. Garzoli, Sabrina Speich, Alberto Piola and Edmo Campos

The third workshop for the South Atlantic Meridional Overturning Circulation (SAMOC 3) took place in Niteroi, Rio de Janeiro, Brazil on May 11, 12 and 13, 2010. A copy of the Agenda, the list of participants and copies of the presentations can be obtained at:

The main objective of SAMOC 3 was to gather international experts to design the basis for an observational program for the Meridional Overturning Circulation in the South Atlantic. Models and observations have shown that strength of the AMOC is significantly correlated with the northward heat transport across 35°S, and hence to the global climate system. The goal of the workshop was to discuss how the present observation systems may contribute to estimating the meridional and inter-basin fluxes of mass, heat and salt; how the existing observational array ought to be upgraded to better capture these fluxes and their variability; and how to transition from the initial observational array to a long-term sustained program. For these purposes it was necessary to determine what parameters should be observed, how to observe them with the best possible observation strategies, where are the observations needed, and who will be interested in carrying them out. The workshop also aimed to foster international cooperation and coordination, which is of crucial importance to fulfill these objectives.

Observations and models consistently indicate that the South Atlantic is not just a passive conduit for the passage of water masses formed in other regions of the world ocean but instead actively participates in their transformation. Water mass transformations occur across the entire basin, but are intensified in regions of high mesoscale variability, particularly at the Brazil/Malvinas Confluence and at the Agulhas Retroflection. Models and observations also show that the South Atlantic plays a significant role in the establishment of oceanic teleconnections. Anomalies generated in the Southern Ocean, for example, are transmitted through inter-ocean exchanges to the northern basins. The Agulhas leakage influence reaches the northern hemisphere and models suggest that changes occurring in the South Atlantic alter the global MOC. These results highlight the need for sustained observations in the South Atlantic and in the choke points in the Southern Ocean, which, in conjunction with modeling efforts, would improve understanding of the processes necessary to formulate long-term climate predictions.

Long-term sustained observations are needed to estimate the net meridional heat, salt and mass fluxes in the South Atlantic. Theoretical model results on the stability of the MOC as well as products of numerical models were discussed and analyzed to determine the optimal latitude to observe the MOC. Based on the results of these models, it is proposed to instrument and sustain a zonal trans-basin South Atlantic line that will, together with ongoing studies in the two Southern Ocean chokepoints sections (Drake and GoodHope), allow for the observation, quantification and attribution of heat, salt and mass fluxes and their changes at a nominal latitude of 35°S. The main in situ array will consist of short moorings on and inshore of the continental shelf break and a mixed array of tall dynamic height moorings and pressure-equipped inverted echo sounders in the interior close to both boundaries. Moored instruments will be deployed with a higher spatial density near the boundaries to measure the deep-water export in collaboration with existing arrays in Drake and GoodHope Passages (the latter may need some additional augmentation). The proposed array will also allow for monitoring of Agulhas ring shedding, and the fate of these rings as they enter the Atlantic due to their potentially crucial role in the meridional salt transport. Further model analyses are ongoing (OSSEs) to decide the precise number and distribution of instruments along the zonal line and along the Good Hope line where the existing mooring array is insufficiently dense for the monitoring purposes proposed herein. A reduced version of the C-Drake array will be deployed at the end of that program to assure the continuation of monitoring in Drake Passage. The working group on model evaluation and design studies is simulating mooring configurations using different combinations of instruments and a variety of models, initially focusing on OCCAM and OFES, later including ECCO2 and NEMO/DRAKKAR.

The crucial role that hydrographic observations in the region can play in support of these moored observations was also discussed. It is proposed to conduct an east-west transatlantic hydrographic survey encompassing the western and eastern boundary current arrays (nominally along 35°S). Full depth hydrography across the south Atlantic will provide detailed information on the baroclinic meridional fluxes between the warm route (Agulhas) and the cold route (Drake). It will provide an assessment of the basin-wide MOC while time series will be built based initially only on the observations along the boundaries. Geochemical and biogeochemical observations will also be collected along the hydrographic sections. These observations will aid in the evaluation of the contribution from each route and their associated variability.

Agreements were made for the sharing of resources, particularly ship-time, from countries at the margins of the basin as well as from countries with ongoing research operations in the South Atlantic. In particular, ships from Argentina, Brazil, Russia and South Africa were proposed for the program. A SAMOC Data Management Plan will be developed that describes the management of data and metadata data within the SAMOC Program.

The meeting was hosted by Edmo Campos (University of Sao Paulo) at the Brazilian Navy's Diretoria de Hidrografia e Navegação (DHN). It was chaired by Silvia L. Garzoli (AOML), Sabrina Speich (LPO, France), and Alberto Piola (SHN, Buenos Aires). The workshop was attended by scientists from Argentina, Brazil, France, the Netherlands, Russia, South Africa, the United Kingdom, Uruguay, and the United States. Funding for the workshop was provided by the NOAA CPO, the US CLIVAR Office, Ifremer (France), the Brazilian Council for Scientific and Technological Development (CNPq), the São Paulo State Foundation for the Support of Research (FAPESP), through the Project INCT-Mudanças Climáticas, and the Brazilian Navy.