The causes of atmospheric CO2 variability during past warm climate intervals are debated. It is widely accepted that changes in carbon sequestration in the deep ocean, in particular in the Southern Ocean, have regulated the atmospheric CO2 variability over as much as the last million years. However, the most basic nature and timing of processes controlling deep-ocean carbon storage during interglacial climates are not understood. We propose to quantify changes in deep-ocean carbon sequestration and to resolve its biological and physical controls during the last warm climate state (Marine Isotope Stage 5) throughout the Southern Ocean. The last interglacial offers an ideal test bed for studying climate feedbacks and -thresholds associated with the global carbon cycle during an 'at times warmer than today' climate. First, we will reconstruct millennial-scale variations in last interglacial deep-ocean carbon content and second, combine these estimates with export production reconstructions to estimate the influence of biological productivity and non-biological (i.e. physical/dynamical) processes on deep-ocean carbon levels, and thus on atmospheric CO2. Third, we will directly quantify changes in surface- and deep-ocean pH to unequivocally determine the efficiency of the partitioning of CO2 between the ocean and the atmosphere. This will provide critical information on the processes and regions that dominate the atmospheric carbon inventory in a warm and warmer-than-present climate, and what eventually leads to a decline of atmospheric CO2 and the demise of an interglacial. This project will provide important benchmarks for a comparison with carbon cycle dynamics of the current Holocene interglacial.
DFG Programme
Research Fellowships
International Connection
USA
