Periodic Reporting for period 1 - OXYPRO (Global biological productivity during abrupt climate change)
Berichtszeitraum: 2021-09-01 bis 2023-08-31
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.
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.
A total of 65 samples of NEEM (The North Greenland Eemian Ice Drilling) ice core has been measured, over ~42 to ~36.5 ka (thousands of years before present) interval that covers Heinrich Stadial 4 (HS4) and Dansgaard Oeschger event 8 (DO8). From the new dataset, the preliminary reconstruction of the global biosphere productivity has been made by using the box-model approach. First of all, the box-models have been modified in order to include the effect of stratospheric changes by considering the recent modelling studies showing the stratospheric changes during the last glacial maximum. In addition, I carried out sensitivity tests in order to understand potential influence of Laschamp geomagnetic inversion event that occurred just before the study period. In the following, I developed a new module that calculates the triple isotopic composition of O2 in the Earth System Model of Intermediate Complexity (EMIC) of iLOVECLIM.
The newly produced data have unprecedently high temporal resolution (~150 years by mean) that allows to reveal the sub-millennial scale changes over HS4-DO8 interval. Previous data from an old Greenland ice core have coarse temporal resolution (larger than ~500 years). The new dataset is therefore the first high-resolution data over abrupt climate change event. In addition, contrary to the previous data set to which only gravitational fractionation effect was corrected, the new records have been corrected by both gravitational fractionation effect and the gas loss fractionation effect. The gas loss fractionation occurs during the long-term storage of ice-core samples, and I found a linear relationship between the gas loss effect and the oxygen to argon ratio from measurements of 15 large samples from two different ice cores. By applying this relationship, the gas loss effect of each sample was measured by simultaneous analysis of oxygen to argon ratio, and the new data have been corrected properly. Resulting triple O2 isotope records clearly show a sub-millennial scale variations, and it is expected to provide invaluable insight into the evolution of global biosphere productivity through the abrupt climate change. In addition, the iLOVECLIM will be the first Earth system model capable of calculating the triple O2 isotopes globally - terrestrial vegetation, atmosphere, and marine ecosystem. As an ESM of intermediate complexity, iLOVECLIM model is able to integrate relatively faster (500 to 700 years per day with carbon cycle) than fully-coupled General circulation models, which is essential for running transient experiments over thousands of years. Once developement is finished, iLOVECLIM model will allow to disentangle the important controls of global biosphere productivity and to estimate quantitatively the role of global biosphere productivity in global carbon cycle through the abrupt climate change.