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The Southern Ocean and Climate Lecture Series

March - May 2011

This winter/spring series will focus on the Southern Ocean and Climate. The lectures will provide students and scientists with a multifaceted appreciation of the role of the Southern Ocean in climate and foster cross-disciplinary interactions.

The Southern Ocean, also known as the Great Southern Ocean, the Antarctic Ocean and the South Polar Ocean, comprises the southernmost waters of the World Ocean, generally taken to be south of 60°S latitude and encircling Antarctica.

A decision by the International Hydrographic Organization in the spring of 2000 delimited a fifth world ocean - the Southern Ocean - from the southern portions of the Atlantic Ocean, Indian Ocean, and Pacific Ocean. The Southern Ocean is now the fourth largest of the world's five oceans (after the Pacific Ocean, Atlantic Ocean, and Indian Ocean, but larger than the Arctic Ocean).

Speaker Schedule

Thursday, May 26, 2011
Carriage House, Quissett Campus
1:30 p.m.

Robert Anderson
Lamont-Doherty Earth Observatory
"The Role of the Winds in Past Climate Change and CO2"

Thursday, April 21, 2011
Clark 507
1:30 - 2:30 p.m.

Hugh Ducklow
The Ecosystems Center
MBL, Woods Hole
"Are Export Flux and Bacterial Productivity Low in Polar Seas? If They Are, Why?"

I will present observations on the export flux and bacterial production measurements from the Palmer LTER region along the Antarctic Peninsula, 1993-2011. Sediment trap results suggest that carbon export from the surface layer is low relative to primary production (PP) rates (export ratio) but recent determinations based on Thorium-234 and Oxygen-Argon ratios yield somewhat higher estimates. However even these higher flux estimates are still low relative to our expectations about high latitude plankton systems. Rates of bacterial production (BP) are also low (<5% of PP), compared to global averages. Temperature limitation does not appear to influence the BP:PP ratio. Rather it appears that bacteria may be limited by the flux of labile dissolved organic carbon from the foodweb. These complementary modes of ecosystem function (export system and microbial loop) are explored using foodweb models.

Wednesday April 6, 2011
Clark 507
3:00 - 4:00 p.m.

Oscar Scofield
Institute of Marine and Coastal Sciences
Rutgers University
"Hot days along the West Antarctic Peninsula: Ecological consequences to regional melting"

Thursday, March 31, 2011
Clark 507
1:30 - 2:30 p.m.

Jim Ledwell
Senior Scientist
Applied Ocean Phyics & Engineering, WHOI
"Mixing in the Antarctic Circumpolar Current"

Mixing in the Antarctic Circumpolar Current, both along and across surfaces of constant neutral density, is believed to play an important role in the transport of heat and carbon dioxide across the Southern Ocean, especially across the latitude band of Drake Passage.  The current state of knowledge of this mixing will be reviewed, including early results from an ambitious field experiment.  Indications so far are that diapycnal mixing is weak, except possibly in the Antarctic Bottom Water and near the surface.  It is too early to assess whether estimates of along-isopycnal eddy mixing will need to be revised.  An attempt will be made to discuss implications of current knowledge for climate change theory.

Thursday, March 17, 2011
Clark 507
1:30 - 2:30 p.m.

Daniel Sigman
Department of Geosciences
Princeton University
"Why the amplitude of glacial/interglacial carbon dioxide change appears to require more than one Southern Ocean change"

The modern Southern Ocean, especially its more poleward Antarctic Zone, releases deeply sequestered carbon dioxide (CO2) to the atmosphere. A consensus has emerged that the observed decline in atmospheric CO2 during ice ages was caused at least in part by a restriction in this Southern Ocean CO2 “leak,” which increased ocean carbon storage both directly and by making the global ocean more alkaline. Reductions in deep water formation and in sea/air gas exchange in the Antarctic (the latter due to sea ice cover) are two popular and related mechanisms for lowering ice age CO2. However, calculations with various models suggest that these “Antarctic ventilation barrier” mechanisms can explain only ~40 of the 80-100 ppm ice age CO2 decrease. As a result, it appears that other changes must contribute substantial portions of the CO2 decrease. A second concern is that southern-source water appeared to fill a larger volume of the abyssal Atlantic during the last ice age, which seems at odds with the hypothesis of reduced Antarctic deep water formation.

Using a modified version of the CYCLOPS box model, and parsing the model’s atmospheric CO2 changes into their component geochemical causes, I will attempt to explain why the Antarctic ventilation barrier mechanisms appear so limited in their CO2 drawdown potential. Then I will evaluate the potential for Southern Ocean nutrient drawdown and shoaling of North Atlantic deep water formation to contribute to the CO2 decline and to fit ice age observations from the deep Atlantic. This will include a hypothesis for how reduced Antarctic ventilation of the deep ocean can be squared with the observation that southern-sourced abyssal water filled a larger volume of the deep Atlantic during the last ice age.

Thursday, March 10, 2011
Clark 507
1:30 - 2:30 p.m.

J. R. Toggweiler
Geophysical Fluid Dynamics Laboratory
NOAA, Princeton, NJ 
"The Mechanism is the Message:  A Comment on the Correlation between Antarctic Temperatures and Atmospheric CO2 During the Ice Ages"

It is widely believed that atmospheric CO2 made the Earth warmer and  cooler during the ice ages.  This belief is based on the temporal correlation between Antarctic temperatures and atmospheric CO2 in ice cores from Antarctica.  We can now say with some certainty, however, that the correlation is mainly due to the mechanism that made Antarctic temperatures and atmospheric CO2 rise and fall together.  The global warming and cooling brought about by atmospheric CO2 (the greenhouse gas) appears to have been considerably smaller and more benign than previously supposed.

David Nicholson, MCG

Last updated: February 29, 2012