Inferring Ocean Circulation During the Last Glacial Maximum and Last Deglaciation Using Data and Models

Daniel Amrhein, Ph.D., 2016
Carl Wunsch, Advisor

Since the Last Glacial Maximum (LGM, ∼ 20,000 years ago) air temperatures warmed, sea level rose roughly 130 meters, and atmospheric concentrations of carbon dioxide increased. This thesis combines global models and paleoceanographic observations to constrain the ocean's role in storing and transporting heat, salt, and other tracers during this time, with implications for understanding how the modern ocean works and how it might change in the future.

  • By combining a kinematic ocean model with ``upstream'' and ``downstream'' deglacial oxygen isotope time series from planktonic and benthic foraminifera, I show that the data are in agreement with the modern circulation, quantify their power to infer circulation changes, and propose new data locations.
  • An ocean general circulation model (the MITgcm) constrained to fit LGM sea surface temperature proxy observations reveals colder ocean temperatures, greater sea ice extent, and changes in ocean mixed layer depth, and suggests that some features in the data are not robust.
  • A sensitivity analysis in the MITgcm demonstrates that changes in winds or in ocean turbulent transport can explain the hypothesis that the boundary between deep Atlantic waters originating from Northern and Southern Hemispheres was shallower at the LGM than it is today.