- Graduate Position
The concentration of atmospheric carbon dioxide (CO2) changed more than 100 ppm over transitions between glacial and interglacial periods (deglaciations) during Quaternary. Among others, the role of global biosphere (terrestrial and marine realms) on the deglacial CO2 changes remains uncertain. In modern climate, the global biosphere uptakes nearly half of atmospheric carbon emitted by anthropogenic activity via photosynthesis (global biosphere productivity), the largest single carbon flux between atmosphere and the biosphere. However, it is challenging to estimate the past global biosphere productivity from local reconstructions as they are often based on indirect geochemical tracers and exhibit spatial heterogeneities. Instead, the triple oxygen isotope composition of air oxygen (17? of O2) preserved in polar ice cores has been proposed as unique tracer of global biosphere productivity of the past. Recent study carried out at LSCE and University of Copenhagen revealed that the global photosynthesis was reduced during the last eight glacial intervals relative to modern value. Nevertheless, the quantitative interpretation of the 17? of O2 data is still complicated because of large uncertainties in the biosphere processes that fractionate the triple O2 isotopes.
This project aims to quantitatively understand the global biosphere productivity change over the last deglaciation. To achieve this goal, the work on this project could involve:
(1) Measuring 17? of O2 and O2/Ar ratio in the air trapped in the recently-drilled EGRIP ice core over the period from 25,000 to 11,000 years before present. The new measurements of 17? of O2 with high temporal resolution (~150 years) will allow to study sub-millennial scale changes of the global biosphere productivity.
(2) Performing numerical experiments under Pre-industrial and Last Glacial Maximum (LGM) boundary conditions by using Earth System Model of Intermediate Complexity (EMIC) iLOVECLIM. The student will also be involved in model development together with the supervisory team.
(3) Conducting transient simulation over the last deglaciation in order to interpret the 17? of O2 variations quantitatively in terms of global biosphere productivity change. This will involve a variety of sensitivity tests and model-data comparison.
(4) Communicating important findings concerning past climate change (and its implication for the future) using both traditional (journal articles, scientific conference) and new/innovative ways of research dissemination.
IMPORTANT: This project is partially (50%) funded by French National Research Council (ANR), and the candidate should pass a selection interview to obtain a complementary funding (50%) by Doctoral School of Environmental Sciences in the Ile-de-France region (ED SEIF). Online application deadline is May 19th 2023. The interview will be held in early June 2023.