EGU General Assembly 2022
© Author(s) 2022. This work is distributed under
the Creative Commons Attribution 4.0 License.

The Southern Ocean during the ice ages: A slumped pycnocline from reduced wind-driven upwelling?

Francois Fripiat1,2, Daniel Sigman3, Xuyuan Ai3, Anja Studer4, Preston Kemeny5, Mathis Hain6, Xingchen Wang7, Haojia Ren8, Gerald Haug2, and Alfredo Martinez-Garcia2
Francois Fripiat et al.
  • 1Department Geosciences, Environment, Society, Université Libre de Bruxelles, Brussels, Belgium
  • 2Max Planck Institute for Chemistry, Mainz, Germany
  • 3Department of Geosciences, Princeton University, Princeton, USA
  • 4Department of Environmental Sciences, University of Basel, Switzerland
  • 5Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, USA
  • 6Earth And Planetary Science Department, University of Santa Cruz, Santa Cruz, USA
  • 7Department of Earth and Environmental Sciences, Boston College, Chestnut Hill, USA
  • 8Department of Geosciences, National Taiwan University, Taipei, Taiwan

The Southern Ocean is recognized as a potential cause of the lower atmospheric concentration of CO2 during ice ages, but the mechanism is debated. In the ice age Antarctic Zone, biogeochemical paleoproxy data suggest a reduction in the exchange of nutrients (and thus water and carbon) between the surface and the deep ocean. We report simple calculations with those data indicating that the decline in the supply of nutrients during peak glacials was extreme, >50% of the interglacial rate. Weaker wind-driven upwelling is a prime candidate for such a large decline, and new, complementary aspects of this mechanism are identified here. First, reduced upwelling would have resulted in a “slumping” of the pycnocline into the AZ. Second, it would have allowed diapycnal mixing to “mine” nutrients out of the upper water column, possibly causing an even greater slumping of the vertical nutrient gradient (or “nutricline”). These mechanisms would have reduced shallow subsurface nutrient concentrations, decreasing wintertime resupply of nutrients to the surface mixed layer, beyond the reduction in upwelling alone. They would have complemented two changes previously proposed to accompany a decline in upwelling: (1) halocline strengthening and (2) reduced isopycnal mixing in the deep ocean. Together, the above changes would have encouraged declines in the nutrient content and/or the formation rate of new deep water in the AZ, enhancing CO2 storage in the deep ocean.

How to cite: Fripiat, F., Sigman, D., Ai, X., Studer, A., Kemeny, P., Hain, M., Wang, X., Ren, H., Haug, G., and Martinez-Garcia, A.: The Southern Ocean during the ice ages: A slumped pycnocline from reduced wind-driven upwelling?, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2047,, 2022.