Seminar 
Temporal evolution of mechanisms controlling  ocean carbon uptake during the last glacial cycle 

When? Wednesday, 8 Mars, 15h00
Where? Högbomsalen, Geovetenskapens hus

 

Many oceanic mechanisms have been proposed to explain the 80–100 ppm decrease in atmospheric carbon dioxide (CO2) during the last glacial cycle, between 127,000 and 18,000 years ago. However, little has been done to determine the sequential timing of processes affecting CO2 during the last glacial cycle. Here I present a new global compilation of sea-surface temperature records, combined with previously documented changes in sea ice extent and ocean circulation, to determine when the most commonly proposed mechanisms could have been important for CO2 drawdown. Our main finding is that a step-wise cooling of the polar ocean played a key role in driving decreases in atmospheric CO2 at the start of the last ice age, primarily via its impact on the southern polar ocean. Initially, the first polar cooling 115,000 years ago is linked to the initial major drawdown of 40 ppm, and an increase sea-ice extent and surface water stratification in the Southern Ocean. Importantly, changes in deep ocean circulation, stratification, or mixing did not play a major role until the second phase of CO2 drawdown at least 30,000 years after the first CO2 drawdown. This occurred ~70,000 years ago and was coincident with the first significant influences of enhanced ocean productivity due to dust. The final minimum concentrations of atmospheric CO2 during the Last Glacial Maximum resulted from the combination of physical and biological factors, including polar surface stratification, enhanced deep ocean stratification, and ocean biological feedbacks.

 
Karen Kohfeld, Guest Seminar at the Department of Geological Sciences, Stockholm University

Dr. Kohfeld is interested in understanding natural variability and biogeochemical linkages within the ocean and climate system, in order to better assess earth system responses to anthropogenic perturbations. Her research focuses on natural and anthropogenic changes in the ocean carbon cycle, the influence of climate and land surface conditions on atmospheric dust, and assessing and adapting to extreme weather conditions in British Columbia.

 

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