Title: A monitoring system for heat and mass transports in the South Atlantic as a component of the Meridio
1A 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
2Objectives
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.
329 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.
4Agenda
- 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)
5Session 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?
7Session 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.
8Session 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).
9Session 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.
10Marcelo 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.
15It 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
16Therefore, 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.
17Main 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.
18In 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.
19http//www.aoml.noaa.gov/phod/SAW/
20Thank you