The concentration of carbon dioxide (CO2) in the atmosphere depends on carbon cycle processes, i.e. sources and sinks of carbon. The future evolution of the carbon sinks is not well known, which inhibits robust quantification of future atmospheric CO2 concentration and the resulting climate change. Understanding warm past periods is essential to constrain climate models and accurately predict future changes. During the last million years, warmer periods, called interglacials, happened every ~100,000 years. CO2 levels measured in interglacials before the mid-Bruhnes event (MBE), a large climate shift taking place ~430,000 years ago, are lower than the CO2 in interglacials after the MBE. The cause for this drastic evolution is still unexplained, resulting in uncertainty in the carbon cycle response to global warming, whose quantification is still subject to large unknowns.
The aim of this project is therefore to reconcile paleoclimate proxy data and model simulations and evaluate if new key processes are necessary to reproduce past climate variations and therefore coming ones. A specific focus will be dedicated to carbon cycle.
It has been suggested that a major mechanism that could explain MBE was a slower circulation during interglacials before the MBE, resulting in more ocean carbon storage and lower atmospheric CO2. Nevertheless, this hypothesis was based on a model that do not include a carbon cycle. We plan to evaluate this hypothesis by using a model including a carbon cycle.
Furthermore, we also propose an alternative hypothesis that is that sea-level changes may have played a considerable role by altering carbon sinks from land vegetation and shallowing ocean carbonate sedimentation, notably by coral reefs.
The objective of the project is to include these mechanisms in a state-of-the-art climate model applicable to long timescales, and compare its modified behavior with paleoclimate data and more complex models used for projections. This will provide a step change in our understanding of the impact of ocean circulation and sea-level changes on the carbon cycle.
It will benefit the European and international scientific community by shedding new light on these processes, and by setting the basis to include these new mechanisms in climate models used for projections, pivotal for adaptation policy to climate change.
