The Fourth CLIVARCliCSCAR panel Southern Ocean Region Panel Meeting

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The Fourth CLIVAR/CliC/SCAR panel Southern
Ocean Region Panel Meeting
Sustained Hydrological Observations
Sabrina Speich the SO Panel
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The Southern Ocean an annular ocean that
connects the world ocean basins
Rintoul et al. 2001
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and transforming meridionally
Rintoul 2001
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This makes the SO a key region for the existence
of a global THC
Because of the lack of observations, the
assessment of this circulation has proven to be
difficult so, till now descriptions have only
been provided as conceptual schemes and
theoretical hypotheses
Schmitz 1996
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MODELS SUGGEST
Decreasing of the North Atlantic Overturning in
future climate
Schmittner et al. 2005
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Very recent high-resolution ice-core data from
Greenland and Antarctica show a coupled behaviour
between the North Atlantic and the southern SH
EPICA group, 2006
Does it have anything to do with the THC as they
propose?
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MODELS SUGGEST
Strong upwelling of NADW in the Southern Ocean
The geographical distribution of the first
upwelling (gamma 27.8)
Indian 1.1 Sv Pac 3.3 Sv Atl 2.2 Sv

• The export occurs via Ekman transport
• The fate is essentially in the Indian and Pacific
  SAMW
• The transformation is due to first a freshwater
  gain (via entrainment in the sub-polar ML) and
  then warming while moving northward gt no heat
  gain in the S Ocean

Iudicone et al. 2006
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MODELS SUGGEST
A complete view of the overturning in the
Southern Ocean
Coupling the watermass formation/transformations
with the Lagrangian analysis
TW gt SAMW
AAIW gt SAMW
Weak AAIW transf.
CDW gt AAIW
CDW gt AABW
Iudicone et al. 2006
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MODELS SUGGEST
Wind induced organization of the global THC
Speich et al. 2006
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MODELS SUGGEST
Changes in wind curl induce change in the
supergyre intensity since 1978
1978-2002 Streamfunction trend
Godfrey (1989) Island Rule Streamfunction
Cai, 2006
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WHAT from DATA ?
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Subsurface floats, HD XBTs, and ARGO improve the
real THC upper branch picture
A SUPERGYRE at SAMW/AIW levels
Davies, 2005
Ollitraut et al. 2006
Ridgwey Dunn 2006
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Long term Southern Ocean Sustained Observations
http//www.clivar.org/organization/southern/CLIVAR
_CliC_Obs.html
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Southern Ocean HD XBT Lines
Drake Passage
(XBT/XCTD/CO2 6-8x per year ADCP 2-4x/mon SIO)
Tasmania-AA (6x/summer - n.b. aliasing
SURVOSTRAL)
Only Drake Passage approaches needed sampling
rate Should upgrade ADCP to deeper profile
AX25 (SA to AA) twice a year (GOODHOPE)
Trans-Atlantic (0-2x/yr NOAA AOML)
NZ-AA (2-4/yr summer - n.b. aliasing CLIMA)
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Complete view of Southern Ocean Hydrological
Observations
http//www.clivar.org/organization/southern/CLIVAR
_CliC_Obs.html
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Repeat Hydrography etc.
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Global Ocean XBT ARGO back in 2003
XBTs (1998)
ARGOas of June 2003
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Global Argo Southern Ocean
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Southern Ocean Argo
Argo array has significantly increased amount of
data available in Southern Ocean However, Argo
will not resolve climate modes until array
extends into the sea ice zone Remember - dots
are large and amount of data we have
(particularly in winter) is still very small even
if it is much much better than before 2003!
http//argo.ocean.fsu.edu/
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Coming out from a desert since Argo
Monthly ML Depth
De Boyer Montegut et al. 2004
Mixed Layer Depth (m)
Sallée et al. 2005
Deep mixed layers SAMW
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Coming out from a desert since Argo altimetry
are there
Sokolov Rintoul 2006
SAF variability
Sallée et al. 2006
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ACC transport from (HD) XBTs altimetry with few
CTDs as starting point (example SAfr-GOODHOPE
section)
Swart et al 2006
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SEaOSSouthern Elephant seals as oceanographic
samplers
Need a better correlation with biologists but if
evaluation of CTD profiles from targeted animals
prove to be in standards, we need to include
these data flow in data centres.
http//biology.st-andrews.ac.uk/seaos/results_ocea
no.htm
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EASTERN BOUNDARIES IMPORTANT FOR THE THC, HEAT
AND FRESH WATER FLUXES ?
Davies, 2005
Ollitraut et al. 2006
Ridgwey Dunn 2006
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Yes, lousy currents but highly non-linear
dynamics need for HIGH RESOLUTION observations
Anticyclones variations in Salinity from
KAPEX(Schmid et al. 2003)
Speich et al. 2006
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Observations ASTTEX strategy seems optimal, need
to continue and implement in other regions
Byrne et al. 2003-2005
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AIR-SEA INTERACTIONS PB of SCALES DIRECT
OBSERVATIONS
P
loss
E
P
gain
E
gain
P
loss
Lumpkin and Speer, 2004
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QuikSCAT BETTER RESULTS
Bentamy 2006
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QuikSCAT BETTER RESULTS but STILL BIASES

• New development of HR regional forecasting models
  (MM5, WRF, ). Need for coupled SO studies?
• Potential for improved Met return from VOS
  (Volunteer Observing System) and increase of IMET
  (Improved Meteorology) equipped ships
• Correction of scatterometer observations
• Blended fields

Chelton et al. 2004
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International Polar Year (Mar. 2007-Mar. 2009)
CASO (CLIVAR SO Panel) Climate of Antarctica and
the Southern Ocean
Chokepoints will try to be almost synoptical and
including specific TEIs observations completing
water-mass budgets and try to better evaluate
heat fresh water fluxes. Need for better
evaluation of air-sea exchanges
CASO http//www.clivar.org/organization/southern/
CASO/index.htm
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Intro
Motivation for GEOTRACES Marine chemistry of
trace elements and isotopes (TEIs) is important
for all aspects of ocean and environmental
science Role of micronutrients in ocean
biogeochemistry (Limitation vs. Control N, P,
Si, Fe, Zn, Mo..) Impact on carbon cycle
(13C vs. Non-traditional isotopes) Rates of
carbon cycle processes (Radiotracers) Tracers
of ocean processes - vertical and horizontal
mixing, benthic boundaries, external inputs,
etc. Transport and fate of pollutants,
especially atmospheric (lead,
mercury) Proxies to reconstruct past ocean
conditions, and the oceans response to
global change
An International Study of the Marine
Biogeochemical Cycles of Trace Elements and
Isotopes TEI
http//www.ldeo.columbia.edu/res/pi/geotraces/
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INTERSECTION of GEOTRACES with CASO TRACE
ELEMENTS ISOTOPES TRACERS FOR WATER MASSES
226Ra surface water activities
228Ra activity 226Ra activity
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Interest of Optical / biogeochemical measurements
for physical oceanography (1)
Estimation of the heating rate of the upper
oceanic layer

• Half of the solar radiation is in IR and absorbed
  by water within the top 10 cm

• The absorption of the other half (visible and UV
  radiations) mostly depends on the presence of
  optically significant substances (phytoplankton,
  detritus and dissolved substances).
• for oceanic water with 0.02 mg Chla m-3
  (oligotrophic gyre) 99 of the radiation
  absorbed in the 0-160 m layer
• for oceanic waters with 20 mg Chla m-3 (strong
  upwelling conditions) 99 of the radiation
  absorbed in the 0-10 m layer

• Measurements of irradiance profiles gt direct
  derivation of heat deposition
• Measurement of biogeochemical quantities (Chla)
  operating model to derive heat deposition.
• Relating heat deposition with diurnal
  stratification?

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VARIABILITY DEEP OCEAN
REGIONALITY
Mean temperature in the Weddell gyre at the
Greenwich Meridian
But Cooling and freshening in the East Antarctic
sector
Farbach et al. 2006
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VARIABILITY DEEP OCEAN
TIME SCALES !!
Observations of deep boundary current at 47N in
the Atlantic from observations (dots) and model
Treguier et al. 2006
Farbach et al. 2006
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Interactions steep topography, open
ocean/continental margin
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STEEP TOPOGRAPHY MIXING
Garabato et al. 2004
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DO NOT forget CONTINENTAL MARGIN, because of
cross exchanges and impact on open ocean water
masses slope currents present everywhere
example NADW fate
Arhan et al. 2003 10 Sv along the African slope
Casal et al. 2006 Naddies along the African
slope
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We start to have some ideas about a mean
thermocline-NADW circulation and related dynamics
(not yet variations), but what about the other
component, the NADW-AABW ??
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International Polar Year (Mar. 2007-Mar. 2009)
SASSI (iAnZone) Synoptic Antarctic Shelf-Slope
Interaction Study
Is a starting point
SASSI http//www.uea.ac.uk/e280/sassi.html
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Last Thought The biggest gap in ocean
observations/modelling/air-sea exchanges is ocean
VERTICAL VELOCITY
We need to use very HR models (1 km horiz
resolution, 300 vertical levels) to access a
first guess for this variable and related
processes