Characterization of the interactions between the carbon cycle and the climate during the marine isotopic stage 7

Etienne Legrain (2020-2023)

Directors : Frédéric Parrenin and Emilie Capron
Funding : HOTCLIM MOPGA project

Summary :
Many uncertainties remain about future and past interactions between climate and the carbon cycle, as well as their impact on components of the Earth system, particularly those that are most sensitive to a warming climate (eg ice caps, sea level, ocean circulation). In this context, the warm periods of the Quaternary, the interglacials, can provide useful information since they offer a series of natural laboratories that allow the study of the processes within the Earth system for a wide range of warm and comparable conditions to today. Between 260 and 190 ka, the interglacial ’Marine Isotopic Stage’ (MIS7) and the preceding deglaciation stand out from the climatic variations of the last 800 ka, by the particular structure of polar warming, and the millennial climatic variability identified at the lower latitudes. However, this time interval has been poorly studied. In particular, the current resolution of atmospheric CO2 recordings does not allow continuous characterization of the variability on a multi-centennial scale of the carbon cycle as well as its phase relationship with other climatic variables at the beginning and then during the interglacial. This thesis provides new information in order to deepen our understanding of the interactions between the carbon cycle and the climate during warm periods of the past. In particular, the objective of this thesis is to identify whether the specificities observed during the MIS 7 interglacial affect the dynamics of the carbon cycle and its link with the climate on a multi-year scale. To do this, it is based on new high-resolution analyzes ( 250 years) of the atmospheric concentration of CO2 and air isotopes (δ15N of N2 and δ18O of O2 ; collaboration with A. Landais from LSCE) from ’air samples trapped in the EPICA Dome C deep ice core drilled in Antarctica given MIS 7 and the preceding glacial-interglacial transition. Accurate quantification of the shifts between CO2 variations and the Antarctic climate will be performed using the δ15N of N2, a tracer responded in Antarctica, to changes in temperature and surface accumulation. The phase study will also benefit from the use of the δ18O of atmospheric O2, which is influenced by changes in sea level, the hydrologic cycle and the productivity of the biosphere at the global scale. These results will also be integrated into a synthesis combining data from marine and terrestrial climate archives in order to reconstruct the climatic context and the sequences of events on a pluri-millennial scale beyond the polar regions during this hot period of the past.

keywords : interglacial, paleoclimate, Antarctic ice core, atmospheric CO2, cryosphere