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Elucidating carbon flow in settling aggregates: a combined isotopic and biomarker approach

The oceans take up 25-30% of the annual anthropogenic carbon emissions and thus play a major role in moderating climate change. Ocean carbon uptake is often conceptualized in terms of carbon pumps in which the biological pump is pivotal. Dissolved carbon dioxide in the surface layer is used by photosynthetic active organisms, converted to particulated forms, exported to the depth and sequestered in bottom waters and sediments. If we gain a better understanding of the biological pump, we could improve our knowledge about reducing atmospheric CO2. Without detailed understanding of the biological pump, we cannot anticipate how future climate change will impact the ocean’s capability to sequester carbon from the atmosphere; this will hamper the accuracy of ocean carbon uptake projections.

Within my PhD I will focus on the transfer of organic carbon from aggregates to microbial metabolism, a process that has so far been largely neglected, despite its crucial role on determining the efficiency of the biological carbon pump. I aim to clarify this key link in marine carbon cycling and focus on the organic geochemistry and microbial metabolism. The key focus will be on the following three queries: (1) Role of aggregate type on carbon export, (2) Temperature controls on aggregate degradation and settling and (3) Sequential degradation and transformation of settling organic matter. The overall aim of this project is to advance our understanding of the biological carbon pump.