Periodic Reporting for period 2 - COS-OCS (Carbonyl Sulphide: new ways of Observing the Climate System)
Reporting period: 2019-03-01 to 2020-08-31
A second link to climate is the uptake of COS by the terrestrial biosphere. COS has been suggested as a possible new constraint on the atmospheric carbon cycle, but only if some large caveats in our knowledge of its budget are resolved. If the COS budget is better understood, there are good prospects to use COS to constrain gross primary productivity (GPP) of terrestrial vegetation. Recent analyses of COS stored in ice cores link observed changes in COS to variations in GPP during the Holocene. Without a drastic reduction in COS source and sink uncertainties and their relation with climate, these claims remain however rather speculative.
The two big scientific questions that are addressed in this reseach are:
1) What is the contribution of COS to the stratospheric sulphate aerosol layer?
2) Can the global budgets of COS and CO2 be reconciled, and what are the implications for terrestrial gross primary productivity?
This is important for society, because the impact of ongoing climate change on the carbon cycle is uncertain. Will large carbon reservoirs become unstable in a warming climate (positive feedback) or will the biosphere take up more carbon (negative feedback)?
Fundamental knowledge about these processes advances our understanding on how these intriguing mechanisms work.
The objectives of the proposed research are to:
1) Perform the first world-wide characterisation of COS isotopologues by measuring seasonal, latitudinal, and altitude variations in troposphere and stratosphere
2) Measure COS gradients over the troposphere–stratosphere transition up to 30 km altitude using innovative AirCore sampling techniques
3) Investigate fractionation effects during soil and plant uptake in laboratory experiments
4) Develop the first model with capabilities to simulate COS-isotopologues and the coupled COS and CO2 cycles
5) Pioneer the use of satellite observations of COS and its isotopologues
6) Constrain the budgets of COS and CO2 using inverse modelling techniques employing surface measurements, satellite data, and new AirCore and isotopic COS measurements
a) we performed a first successful campaign with the novel AirCore technique. With a balloon a thin tube is brought to the stratosphere and on descent air is sampled. This resulted in the first COS profiles in the stratosphere.
b) we developed a model for COS. Using surface observations we are able to optimise the surface fluxes such that observations are almost perfectly fitted world-wide (see illustration)
c) we have been able to simulate and evaluate exchange of COS with the biosphere. We use a mechanistic model called SiB4. This model is being further developed in cooperation with the scientific community
d) we developed a technique to measure the S-isotopologues of COS. We measured COS (& isotopologues) in air sampled from the stratosphere that we had available in our lab. Results are currently being analysed.
e) we compared our model results to satellite observations of COS.
2) We are the first that are able to conduct AirCore measurements of COS in the stratosphere. We also managed to embark our equipment on HEMERA, a balloon experiment that will sample stratospheric air. We are determined to get air samples from the stratosphere from this campaign.
Currently we have the first publications in the writing phase. We expect 4 PhDs to graduate on COS-OCS research. (1) COS inverse modelling and isotope modelling (2) COS-CO2 coupled inverse modelling (3) AirCore analysis of COS (4) isotopologue measurements of COS.