The interglacial CO2 mystery – TICMY

CO2 plays a crucial role in the climate. However, changes in CO2 concentration during the warm interglacial periods of the last 800,000 years remain unexplained. In particular, the CO2 concentration during the "old" interglacials before the Mid Brunhes Event (MBE, about 430,000 years ago), is lower by about 25 ppm compared to the more recent interglacials. Existing studies have focused on changes in ocean circulation, which cannot explain the full magnitude of the CO2 difference nor the available carbon isotope data, which nevertheless constitute a strong constraint on the carbon cycle. During the ancient interglacials sea level was probably lower and the ice sheets more extensive. These changes likely resulted in reduced coral reef development and expanded permafrost. Furthermore, this would have altered the exchange with marine sediments, modifying the balance of carbonate ions, and ultimately the concentration of atmospheric CO2.
In this project, we are going to quantify the impact of these three key components of the carbon cycle, which have not yet been considered over these time periods: coral reefs, permafrost and marine surface sediments. For this, we will use the coupled climate-carbon model iLOVECLIM which is fast (700 years/day) and therefore perfectly suited to the study of changes over several millennia. As iLOVECLIM simulates carbon isotopes, it allows us to evaluate the results of the model by comparing to existing benthic foram and ice core d13C data. We will assess the impact of coral reefs and sediments on the carbon cycle during the interglacials of the last 800,000 years. We will implement and quantify the impact of permafrost. Finally, we will study the evolution of CO2 concentration due to these processes in the future, in response to anthropogenic emissions.