Executive Summary

South Atlantic Meridional Overturning Circulation (SAMOC) - Fourth Workshop*


The fourth workshop for the South Atlantic Meridional Overturning Circulation (SAMOC 4) took place in Simons Town, South Africa, during September 26-28, 2011. The main objectives of the workshop were: to highlight recent modeling results related to the importance of observing the South Atlantic components of the Atlantic Meridional Overturning Circulation (AMOC); to provide an overview of results from ongoing pilot arrays and related observational programs; to discuss the status of proposals submitted for observations and modeling; and to coordinate new proposals aimed at SAMOC goals. In addition, ship time availability to support the proposed fieldwork in the region, and to reach new agreements for sharing these resources were discussed.

In the morning of the first day local scientists made several short presentations on science relevant to the SAMOC goals. These presentations focused on role of Agulhas eddies in the South Atlantic and highlighted the significance of recent changes in surface temperature, wind stress and wind stress curl associated with southward displacement of zonal winds. Brief presentations were made on new modeling results and observations followed by plenary discussions on current and future plans. A review of recent results from ongoing modeling experiments demonstrated that 30-35°S was the best latitude to monitor the MOC variability, confirming previous results derived from the analysis of numerical and theoretical modeling studies conducted in the United States, the United Kingdom, Brazil and the Netherlands. First and foremost, higher latitudes provide stronger density gradients and larger Coriolis parameter, leading to improved signal-to-noise characteristics for geostrophic velocity calculations. Secondly, the strongest signals are more tightly confined to the boundaries at higher latitudes, particularly at the eastern boundary, indicating that a smaller portion of the trans-basin array requires more intense horizontal resolution. Thirdly, estimation of the stability of the MOC, a crucial factor in attribution of observed signals, is more favorable at higher latitudes. Finally, ocean model studies indicate that at higher latitudes it is possible to utilize less expensive mooring technologies (i.e. pressure-equipped inverted echo sounders – PIES), reducing the cost of the overall system and its maintenance.

Status and future plans for existing observing programs were discussed. Details of the funded, submitted and to be submitted projects are given in the attached Table.

One crucial component of the overall SAMOC observing system, the proposed trans-basin array at 34.5°S, was thoroughly discussed including a review of the comments of the anonymous reviewers of this US-NSF proposal. The consensus of the workshop attendees was that the proposal be resubmitted with modifications. The array will be proposed with ~20 ocean moorings, a combination of tall ‘dynamic height’ moorings and PIES, coupled with several shorter direct velocity moorings on the shelf on either side of the basin.

Measurements at the boundaries were considered crucial to close the budgets. A group of North and South American countries operating through the Inter-American Institute for Global Change Research (IAI) has a large shelf-monitoring program funded for western boundary that would fit together nicely with the western end of the recommended trans-basin array. In addition a Brazilian proposal was funded for augmenting the shallow array close to the current US-funded PIES deployed at 34.5°S. At the eastern boundary, South African scientists at the Centre for Operational Oceanography were funded to deploy an array of 5 ADCP moorings from the coast out to the French array of CPIES.

The group was in agreement that attribution of the observed signals at 30-34.5°S will require both the continuation and augmentation of the existing concurrent interocean exchange observing systems: the GoodHope array and the Drake Passage programs. Observations along the GoodHope transect will, in conjunction with the German array of PIES/CPIES and altimetry, help quantify the Agulhas rings shed at the retroflection, while the Drake Passage observations will aid in determining flow via the cold-water route. The group also agreed it was important to analyze the products of different ocean general circulation models to study the different branches of the Deep Western Boundary Current in the South Atlantic.

Crucial to the success of the program will be the availability of an impressive research fleet. South Africa is building a new global class ship that will become operational in 2012. The University of Sao Paolo has purchased a regional class ship that will also be available in 2012. Brazilian scientists have also obtained funds to buy new oceanographic equipment and refurbish the Brazilian Navy vessel Cruzeiro do Sul. In Argentina, in addition to the currently available R/V Puerto Deseado, a 40 foot catamaran will be available for near shore mooring services.

One action item from the workshop is the preparation of a SAMOC implementation plan to be submitted to International CLIVAR for endorsement. The SAMOC V workshop will take place in Miami, US. Local organizers will be Renellys C. Perez and Chris Meinen.

The SAMOC IV workshop was hosted by Isabelle Ansorge and Chris Reason (University of Cape Town). It was chaired by Silvia L. Garzoli (AOML, USA), Sabrina Speich (LPO, France), and Alberto Piola (SHN, Argentina). The workshop was attended by 43 scientists and students from eight countries (Argentina, Brazil, France, Germany, United States, United Kingdom, Spain, and South Africa). Support from the workshop came from the South African National Antarctic Programme (SANAP) Development Grant and the Johann Lutjeharms NRF rated researchers award.

*The meeting was dedicated to the memory of Johann Lutjerhams, UCT’s Professor, one of Southern Africa’s leading marine scientists and the foremost authority on the Agulhas Current, who died on 8 June 2011.


Component

Funding Agency

Principal Investigators

Country

Status

Western boundary pilot measurements (4 PIES, 1 spare)

NOAA

C. Meinen, S. Garzoli, M. Baringer, G. Goni

USA

Funded

Quarterly AX18 XBT transect + Argo floats

NOAA

G. Goni, M. Baringer, S. Garzoli

USA

Funded

Twice a year transect AX25 + Argo floats

NOAA/UCT

Garzoli, Goni, Ansorge

US/South Africa

Funded

Eastern boundary pilot measurements (4 CPIES)

IFREMER/CPER

S. Speich

France

Funded

Eastern boundary ADCPs (5)

South Africa, IFREMER

M. Roberts, S. Speich

 

South Africa, France

Funded

Goodhope PIES (7), CPIES (7), current meter (5)"

Germany

A. Macrander, O. Boebel

Germany

Funded

Western boundary ADCP (1), BPR (1), western boundary hydrographic, turn-around, recovery cruises

CNPq/INCT

E. Campos F. Niencheski

Brazil

Funded

The CALSA Project (Numerical Modeling)

FAPESP

E. Campos

Brazil

Funded

The ATLAS-B, the NAP-MC and FAPESP-MC Projects (Atlas mooring, currentmetry and cruises in the Santos Bight, ~23-28S)

FAPESP, CNPq-INCT &USP

E.Campos

Brazil

Funded

The South Atlantic Climate Change Consortium (SACC).Shelf/slope observations and models

IAI

A. Piola , E.Campos/R. Matano/K.Brink/M. Barreiro

Argentina/ Brazil/US/Uruguay

Funded

Drake Passage, XBT and CTD SADCP lines

NOAA, Shirshov , NOCS

J. Sprintal, S. Gladyshev, B. King

US, Russia, UK

Funded

CTD section in the South Atlantic 40°S (can be moved north)

Univ. of Barcelona

J.L. Pelegri

Spain

Funded

Western boundary PIES (4), interior PIES-DP (4)

NOAA

R. Perez, S. Dong, C. Meinen, G. Goni, S. Garzoli, M. Baringer

USA

Proposed

Western boundary CPIES (3), western boundary hydrographic, turn-around, recovery cruises

FAPESP/ FACEPE

E. Campos A. Fetter

Brazil

Proposed

(1) Eastern boundary CPIES (6),

ANR

S. Speich

France

Proposed

(2) Goodhope PIES (7),

(3) Marisonde buoys (5)

shelf circulation along altimeter line near 40S

France Argentina MOU

A. Piola, C. Provost

Argentina/France

Proposed

(1) Dynamic height moorings (8) (2) Deployment and trans-basin hydrographic cruise

NSF

S. Dong, R. Perez, J. Sprintall, R. Fine, G. Flierl, S. Baker-Yeboah

USA

To be proposed

24?S western boundary moorings, trans-basin hydrographic cruise

NERC

E. McDonagh

UK

To be proposed

Western boundary instrumentation, western boundary hydrographic, turn-around, recovery cruises

Argentina

A. Piola, A. Triosi

Argentina

To be proposed

Western boundary (possibly trans-basin) hydrographic cruise

Spain

J. Pelegri

Spain

To be proposed

Eastern boundary hydrographic, turn-around, recovery cruises

SANAP

I. Ansorge, C. Reason

South Africa

To be proposed

Goodhope hydrographic, deployment, recovery cruises

Russian Acad. Sci.

S. Gladyshev, A. Sokov

Russia

To be proposed

SAMOC RELATED PROGRAMS





The INCT-Mar-CARBOM and INCT-Mar-COI Projects

 

 

Brazil

Funded

OOI

NSF

WHOI/SIO

USA

Funded

Weddell Sea current meters (8) and BPRs Germany/UK AWI/BAS Germany/UK Funded