The global biosphere (terrestrial vegetation and marine ecosystem) absorbs about the half the carbon emitted by human activity nowdays, via photosynthesis, contributing to reduce its impact. Since the photosynthesis is the largest single flux of carbon, for a better projection of future climate, it is essential to understand how the global biosphere would respond to upcoming climate change. Recent observations show that the global photosynthetic flux changes with climate variations - for example, atmospheric carbon dioxyde (CO2) concentration or air temperatre -, however, the major control of the global biosphere productivity is not well understood primarily because of (1) lacking long-term observation of global productivity, and (2) indirect and qualitative nature of paleoproductivity proxy records from sediment cores that complicates the estimate of global biosphere productivity of the past.
This project will alleviate both problems by measuring triple isotope composition of air oxygen (O2) from the ancient air trapped in polar ice cores. The triple isotopic composition of O2 is a unique tracer of global biosphere productivity, and the polar ice core is the unique archive that preserves the ancient atmosphere in air bubbles that allows to study directly the composition of past atmosphere over the last 800 000 years. In particular, OXYPRO project aims to reconstruct the variations of the triple isotopic composition of O2 with the highest temporal resolution over the abrupt climate change events occurred during the last glacial period. These events are accompanied by abrupt warming of up to more than 10 degrees within a few decades showing a drastic change in climate and environement at global scale, and hence these events provide an optimal natural experience to study the response of global biosphere productivity to upcoming abrupt climate change and hence its impact on global carbon cycle.
To achieve the goal, the objective of OXYPRO projet is twofold: (1) to reconstruct the high-resolution records of triple isotopic composition of O2 and carbonyl sulfide (COS) concentrations over the transitions of Heinrich Stadial (HS) to Dansgaard-Oeschger (DO) events from ice cores drilled in Greenland, and (2) to make quantitative interpretation of the new data by using Earth system model equipped with triple O2 isotopes.
