Constraints on the carbon dioxide (CO2) deglacial rise based on its stable carbon isotopic ratio (δ13CO2)

The present work is based on the measurement of carbon dioxide (CO2) and its stable isotopic ratio δ13CO2 in air bubbles trapped in polar ice (EPICA core, Dome C, in Antartica, EDC). We focus on rapid transitions from glacial to interglacial periods. δ13CO2 allows the partitioning of the origin of CO2 between oceanic and terrestrial sources. This study documents with high temporal resolution the evolution of CO2 and δ13CO2 during the two last deglaciations. The last deglaciation is characterized by an increase of 80 ppmv CO2, coeval with a decrease of 0.6 ‰ in δ13CO2. Larger amplitudes were observed during the penultimate deglaciation (+110 ppmv CO2 with a 0.9 ‰ decrease in δ13CO2). The measurements, interpreted with two carbon cycle models (BOXKIT and BICYCLE) are consistent with the following scenario. First, a Southern Hemisphere warming triggers an increase in atmospheric CO2. This provokes a biological and physical reorganization of the Southern Ocean which reduces δ13CO2. Last, this reorganization propagates to the north with a delayed impact of terrestrial biosphere during the Bolling/Allerod (B/A). These results obtained for the first time from the EDC core allowed to propose a scenario on the causes of deglaciations. A series of tests, based on ice of different properties, provided a validation of our extraction method.