www.csiro.au the global influence of the southern ocean steve rintoul centre for australian weather...
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www.csiro.au
The Global Influence of the Southern Ocean
Steve Rintoul
Centre for Australian Weather and Climate Research
Wealth from Oceans National Research Flagship
Antarctic Climate and Ecosystems CRC
Hobart, Tasmania , Australia
Global warming is ocean warming
Levitus et al., 2004
OCEAN
LAND
ICE SHEETS
ATMOSPHERE
SEA ICE
GLACIERS
84% of warming since 1955 is found in the ocean.
Loss of Antarctic ice: melt by a warmer ocean?
Antarctic mass loss increased by 70% in last decade, as a result of warmer air and sea temperatures.
Rignot et al., Nature Geoscience, 2008
New gravity measurements suggest larger than expected ice loss in East Antarctica.
Chen et al., Nature Geoscience, 2009
Dense water formed in the Southern Ocean has become fresher and less dense since 1970.
Rintoul, GRL, 2007
Acidification of the Southern Ocean: 450 ppm is the “tipping point”
Orr et al (2005)
McNeil & Matear, PNAS, 2008
If take seasonality into account, SO will be undersaturated with respect to aragonite by 2030. Corresponds to atmosphere concentration of 450 ppm.
Large regional changes in Antarctic sea ice
Stammerjohn et al. (2008)
Changes in sea ice duration: 1979 – 2006
-83 23 days
57 13 days
Future of the Southern Ocean
Warmer, more precipitation
More stratified (less nutrient input?)
Weaker overturning circulation?
“Saturation” of carbon sink?
More acidic (ecosystem impact?)
Increased melt of floating glacial ice, faster sea-level rise
Less sea ice (fewer krill + krill predators?)
Southward shift of ocean currents and habitat
Southern Ocean science and policy
To educate, to inspire and to raise awareness of the global influence of the Southern Ocean.
To detect change and assess the likelihood of abrupt change.
Source of better climate projections, from models that include a better representation of Southern Ocean processes.
Wise stewardship of marine resources.
Protecting lives and the environment in the face of a growing human presence in Antarctica.
Summary
The Southern Ocean has a profound influence on the earth system.
Changes in the Southern Ocean will affect climate, sea level and marine resources. Change observed to date likely linked to the Southern Annular Mode.
To respond to the challenges of a changing climate, knowledge of how the Southern Ocean will respond to and drive climate change is critical.
Sustained observations are key. The IPY demonstrated that a Southern Ocean Observing System is feasible, cost-effective and essential.
Rintoul, Hughes and Olbers 2001; Sokolov and Rintoul 2007a,b
Bottom pressure torque (color); streamfunction (black)
Barotropic vorticity (~ angular momentum) balance
ßx = pbH + + FNorth-south = bottom pressure + curl of wind + curl of nonlinear
flow torque stress terms
Hot spots of biological productivity
A dynamical recipe for the world’s largest ocean current
• winds and buoyancy forcing drive a current around Antarctica• density surfaces tilt up to the south, in balance with current• eventually the current goes unstable, spawning eddies• eddies transfer momentum downward, and heat and mass poleward (so east-west and north-south flows are coupled)• vertical transfer of momentum sets up deep currents• interaction of deep currents with bathymetry establishes stresses on the sea floor to balance momentum and vorticity budgets.
We now understand the circumpolar current and overturning circulation are intimately linked:
Summary
The Southern Ocean and Antarctica are changing.
SO changes will have global impact.
Models still fail to capture key SO processes, so nature of future change remains uncertain.
Observations are critical for model testing and improvement and to determine climate trajectory.
A Southern Ocean Observing System is feasible, cost-effective, and urgently needed. Need to add something re policy.
Summary
The Southern Ocean links the upper and lower limbs of the global overturning circulation, and therefore has a strong influence on the earth’s climate.
The three-dimensional circulation of the Southern Ocean reflects a delicate balance between wind and buoyancy forcing, water mass transformation, eddy fluxes and topographic interactions.
The present revolution in ocean observations will enable a major leap forward in our understanding of ocean climate processes and in our ability to predict future changes in climate and their impacts.
Acknowledgments
Students: Bernadette Sloyan, Helen Phillips, Guy Williams, Andrew Meijers, Katy Hill, Laura Herraiz-Borreguero, Steph Downes
Collaborators: Serguei Sokolov, Dirk Olbers, Kevin Speer, Mark Rosenberg
Mentors: Trevor McDougall, John Church, Carl Wunsch, Arnold Gordon
Support: CSIRO, Australian Antarctic Division, Australian Greenhouse Office, CRC program
At sea: officers and crew of RSV Aurora Australis, Astrolabe, RV Franklin, FRV Southern Surveyor, family coping with long absences
Sea Mammal Research unit
MAMVis-AD
CEBC-CNRS
Kerguelen
Antarctica
1200 m
Sea temperature
Biuw et al., PNAS, 2007