Atlantic Meridional Overturning Circulation: The South Atlantic MOC international initiative: Status and preliminary results

SPEICH, S.; MEINEN, C. S.; PIOLA, A. R.; CAMPOS, E. J. D.; GARZOLI, S. L.; M. ROBERTS; I. ANSORGE; PEREZ, R. C.; DONG, S.; CHIDICHIMO, M. P.; VAN DER BERG, M.; KERSALE, M.; GONI, G.; TERRE,T.

Qingdao

Conferencia; CLIVAR Open Science Conference; 2016

CLIVAR

The meridional overturning circulation (MOC) is a primary mechanism for the transport and storage of heat, freshwater and carbon by the ocean and therefore has a large impact on climate variability and change. The transport of properties by the MOC depends on the rate of overturning and the difference in property concentration between the upper and lower limbs of the overturning as well as well as modification of water properties along their global journey. Therefore observations of the MOC must extend throughout ocean basins to quantify changes in the MOC and to determine their cause and impact. This expansion requires an increased international commitment to the design and maintenance of the observing network and the implementation oftechnologies for collecting deep ocean data and transmitting these data to shore in a cost effective manner. In particular, it is critical to monitor flow rates and properties at sites where upper ocean waters are injected into thedeep ocean and where these waters are exchanged between sub-basins. Within the MOC, the South Atlantic Ocean plays a key role as a nexus for water masses formed elsewhere and en-route to remote regions of the global ocean. Because of this important interbasin exchanges, the South Atlantic Ocean is the only major ocean basin that transports heat from the pole towards the equator. However, the South Atlantic is not merely a passive conduit for remotely formed water masses. Indeed, within this basin water masses are significantly altered bylocal air-sea interactions and diapycnal/isopycnal fluxes, particularly in regions of intense mesoscale activity and steep topography. These contributions have been shown to have a crucial role in the strength of the MOC inpaleoceanographic and modelling studies. The monitoring of the North Atlantic portion of the MOC has beenongoing for a decade now through the RAPID/MOCHA/WBTS program as well as other national and international initiatives. They all provide a scope for understanding the MOC variability in that region. Given thecomplex, multibasin nature of the MOC, achieving a more complete understanding of its behaviour and changes requires a more comprehensive observing system, one that extends across neighbouring ocean basins as the onewe are developing for the South Atlantic within the CLIVAR SAMOC initiative. In this presentation, we will discuss the SAMOC Initiative observing and modelling status. Moreover, we will present the various ongoing MOC estimates (from high-resolution XBTs, Argo, satellite altimetry and models) and revisit the estimates of the daily MOC strength at 34.5°S obtained during a ~20 month long pilot array between 2009 and 2010 with recently recovered data covering almost three additional years (2012-2015).. The new results will be also compared to the long-term (10-year) estimates from the 26.5°N RAPID/MOCHA/WBTS array. The resulting variability is partitioned in terms of total, Ekman, geostrophic and boundary volume transport components. We will also discuss the variability of the transport due to eastern-boundary eddies (Agulhas rings, cyclones, etc) from the analysis of 2 year CPIES data in the Cape Basin and multisatellite sea-level data.