Marine Biogeochemistry: large scale distribution of inorganic carbon and its stable isotopes

The project is related to marine biogeochemistry, with emphasis on large-scale distribution of inorganic carbon and its stable isotopes in the global ocean based on analyses of observations, with a particular focus on the influence of anthropogenic CO2 on the marine carbon isotope composition, and its implications. The oceanic ratio between the two stable carbon isotopes 12C and 13C (expressed d13C) is decreasing with the intrusion of anthropogenic CO2 from the atmosphere. Oceanic d13C is commonly used a s a frame of reference to interpret changes in fossil foraminiferal d13C records, the primary tracer for understanding changes in past water mass distribution and ocean ventilation. However, when isotopically light anthropogenic CO2 propagates into the oc ean interior, the natural d13C gradients are weakened and the d13C distribution becomes more homogeneous. This makes the observed d13C distribution an improper frame of reference for the interpretation of sedimentary records. By quantifying this decrease, we can reconstruct the preindustrial d13C (d13pi) distribution, and re-evaluate the driving forces setting oceanic d13C. Proposed work at UW The high northern latitudes is an important region with respect to the formation of deep water masses that flow into the Atlantic Ocean, but the d13Cpi distribution of the Arctic Ocean is unclear. By using data from the Arctic and the Nordic Seas, we will study the d13C in this region, in particular with regard to the contrasts between waters entering the Arctic f rom the North Atlantic and the waters flowing southwards out of the Arctic. First, we will correct for the intrusion of anthropogenic CO2 with a back-calculation method, and reconstruct the d13Cpi. This allows us to study the natural processes that set d1 3C in this region. We will also look at the ratio between the decrease in d13C and estimates of anthropogenic carbon, which can provide insights on the mechanisms of anthropogenic carbon uptake in this region.