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Title: A monitoring system for heat and mass transports in the South Atlantic as a component of the Meridio


1
A monitoring system for heat and mass transports
in the South Atlantic as a component of the
Meridional Overturning Circulation Estancia San
Ceferino, Buenos Aires, Argentina May 8, 9, and
10, 2007
2
Objectives
The main objective of this workshop was to get
together scientists with current or proposed
programs in the South Atlantic to foster
collaborations leading to the establishment of a
monitoring system for meridional heat and mass
transports in the South Atlantic and inter-ocean
exchanges as a component of the Meridional
Overturning Circulation. The objective was
reinforced by the recommendation of the Joint
Subcommittee for Ocean Science and Technology to
include Assessing MOC Variability in the Atlantic
as a US mid-term priority.
3
29 participants from Argentina, Brazil, France,
Germany, Italy, Russia, Uruguay, UK, and the US
attended the workshop.
The workshop received financial support from the
NOAA CPO and from the US CLIVAR office.
4
Agenda
  • Session 1
  • Introduction and objectives of the Workshop
    (Garzoli)
  • AMOC as a US Ocean Priority (Lindstrom)
  • Messages from Mike Johnson and Jim Todd
    (Garzoli)
  • The Aquarius/SAC-D Program (Lagerdof, Colomb)
  • Argo (Piotrowicz)
  • The South Atlantic Circulation and its role in
    Climate (Piola)
  • Inter-ocean exchanges. Large scale observations
    and models (Speich)
  • Will slowing of the MOC warm or cool Europe?
    (Nof)
  • The impacts of changes in the MOC on the south
    Atlantic climate and variability (Campos)

5
Session 2.1 Inter-ocean exchanges
Pacific/Atlantic Session 2.2 Inter-ocean
exchanges Indian/Atlantic Session 2.3 Meridional
inter-hemispheric fluxes
6
  • The format of session 2 was as follows
  • Participants were invited to make short (3 to 4
    slides) presentations leading to answer the
    following questions for each of the three topics
    above
  • Methodologies
  • What observations are in place?
  • What observations are proposed?
  • What is the objective of each one of the
    programs?
  • What are the observations telling us?
  • Can these plans be integrated to build an
    ocean-scale observing network/experiment?
  • What validation of models has already been done
    in the region?
  • What are the models telling us?

7
Session 2.1 Inter-ocean exchanges
Pacific/Atlantic
  • Drake Passage is a key chokepoint for one of the
    worlds largest current, the Antarctic
    Circumpolar Current (ACC).
  • Heat, salt, mass, freshwater, nutrients etc. are
    moved between the Atlantic, Pacific and Indian
    Oceans, with consequences for global climate,
    ecosystems etc.

Therefore it is important to know what
variability the oceanic circumpolar flow exhibits
on a range of timescales, and how it interacts
with lower latitudes.
8
Session 2.3 Meridional inter-hemispheric fluxes
The Agulhas leakage region is also of critical
influence. It is not only the gateway for the
upper limb of the MOC return flow, but through
the shedding of Agulhas rings is one of the major
sources of salinity increase of the South
Atlantic.
  • The variability of the leakage observed in
    paleo-times appears to be linked with the
    Atlantic MOC intensity.
  • Of particular concern were the failure of the
    most state-of-the-art eddy-permitting and
    eddy-resolving simulations (e.g., POP 1/10
    OCCAM Japanese experiment) to simulate the
    correct path of the Agulhas eddies because these
    particular features are thought to be integral
    components of the MOC (contribute to inter-ocean
    fluxes and water mass conversions).

9
Session 2.3 Meridional inter-hemispheric fluxes
Meridional heat flux model comparisons
Monitor temperature and salinity concurrently
with velocity if want variability in heat
freshwater fluxes.
Stream function of meridional overturning in the
Atlantic, based on a model constrained by
observational data ECCO, after Köhl, et al.,
2007.
10
Marcelo Barreiro
11
  • Observations and models suggest that the South
    Atlantic is not a passive conduit for remotely
    formed water masses, but that it actively creates
    them through dynamic and thermodynamic processes
    occurring within the basin.

12
  • MOC variability can be linked to the equatorward
    heat transport at mid latitudes within the basin
    that operates over longer time scales than
    surface fluxes and hence, could potentially
    provide some predictability for climate.
  • Discernable changes in tropical SST appear to be
    strongly linked to the eastern boundary
    circulation in the South Atlantic and in fact
    global SST is linked to the South Atlantic
    Subtropical heat transport.

13
  • Presentations pointed to the critical importance
    of accurately observing and monitoring the
    subtropical boundary currents in order to
    estimate the MOC mass, heat and freshwater
    transports.

14
  • It was concluded that a better understanding and
    quantification of the circumpolar variability and
    the Agulhas leakage on a range of timescales, and
    how these changes impact the lower latitudes was
    sorely needed, in particular to design a
    monitoring system that might be capable of
    measuring heat and salt fluxes.
  • Observations not only at the choke points but at
    the interior of the basin are critical to
    understand the processes.

15
It was agreed that very little is currently in
place or even proposed that is capable of
capturing the complete MOC as a sustained
observing system.
Plans were established to coordinate existing and
future observations
16
Therefore, discussions were directed towards the
design of a monitoring system for the Atlantic
MOC in the South Atlantic.
The need for new developments in the present data
collection system as well as the need to collect
data at climate time scales (e.g. a sustained
commitment for a decade and more of observations
in near real time). Modeling results indicate
the need to increase observations not only in the
choke points but also in the interior of the
South Atlantic basin where water mass
transformations occur and large discrepancies
exist in numerical models and between numerical
models and observations.
17
Main recommendations
  • More strategic thought about what the separate
    elements are telling us, and how they are
    connected.
  • Collaboratively analyze the different data sets
    and model products presently available and soon
    to be obtained, as well as to conduct process
    modeling studies to determine the most cost
    effective monitoring system for the MOC in the
    South Atlantic for climate time-scales.

18
In the mean time.
  • It is imperative to sustain the existing
    observations in the three key regions mentioned
    above and to further enhance the observing
    system.
  • There is a strong need to develop new cost
    effective technology to allow near real-time full
    water column observation.
  • Commit to having instrumentation in situ
    long-term.
  • Monitor temperature and salinity concurrently
    with velocity if want variability in heat
    freshwater fluxes.
  • It is critically important to collaborate in the
    instrument deployments to reduce operational
    costs.

19
http//www.aoml.noaa.gov/phod/SAW/
20
Thank you
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