Master thesis defense by Marta Agnieszka Mrozowska

Title: "Hitting rock bottom: How the Earth system resists cooling and/or lowering atmospheric CO2 concentrations during the glacial periods"

Abstract: "Over the past 800 thousand years, the Earth system has gone through a series of glacial-interglacial cycles. The glacial paleo-climatological records show a consistent lower limit for both the atmospheric CO2 levels and the temperature. This motivates a hypothesis that a potential negative feedback effect is in place which keeps the Earth system above these limits. In this work, five of the negative feedback hypotheses are presented, described in detail and tested using output from fully coupled Community Earth System Model. The modeled glacial conditions match the observed Last Glacial Maximum CO2 levels and temperatures. The output analysis reveals that the lower CO2 limit does not exist in the model, but the temperature limit does. Nutrient trapping, found in previous model studies, is also present in the output. The productivity in the global ocean is limited due to high phytoplankton activity in the Southern Ocean, which could be a potential overlooked negative feedback effect."

Supervisor: Markus Jochum

Censor: Søren Larsen (DTU)

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