Testing model representation of seasonal air-sea exchange of O2 and CO2
The processes driving air-sea CO2 exchange are not understood well enough to support predictions of future atmospheric CO2 trends. Diagnosing ESM air-sea CO2 fluxes and their drivers is difficult owing to sparse ocean observations and competing thermal and biological influences. Atmospheric measurements provide larger scale constraints and adding O2 enables unique insights into the processes influencing air-sea CO2 exchange.
We now have a wealth of atmospheric O2 and CO2 observations, from the 5 HIPPO and 4 ATom global airborne surveys, as well as the ORCAS intensive Southern Ocean campaign, and shipboard and station records. The seasonal amplitude in column-mean atmospheric potential oxygen (APO = O2 + CO2) from HIPPO and ATom are surprisingly symmetric in each hemisphere, in disagreement with preliminary model comparisons. Further, measurements of O2:CO2 ratios in spatial gradients over the Southern Ocean from stations, ships, and aircraft reveal consistently negative values indicating biological dominance of seasonal CO2 exchange, but in disagreement with a subset of CMIP5 models. Having abiotic CO2 from the models will be particularly useful for evaluating the ability of observed O2:CO2 flux ratios to discern forcings.
From available historical simulations, extract gridded monthly air-sea O2, CO2, and heat fluxes as well as SST and salinity fields. Calculate latitudinal distributions of seasonal net outgassing of APO and compare to similar quantities derived from the HIPPO and ATom data. Calculate O2:CO2 ratios over the Southern Ocean, evaluate spatial patterns and coherence, and calculate spatially integrated timeseries. Regridding all fields to a common 1 x 1 degree grid would be helpful, but may not be necessary. (The heat, SST, and salinity are required to estimate air-sea N2 fluxes to make a small correction to the O2 fluxes to match the observed atmospheric quantity which is deviations in the O2/N2 ratio). Compare bio vs thermal forcing ratio implied by O2:CO2 to that from model abiotic CO2 flux.
Anticipated Data Needs
Air-sea O2, CO2, and heat fluxes as well as SST and salinity fields from historical simulations.The last 20 years of the simulations will be the focus but earlier times may be useful for evaluating trends.
I put a request in for historical + Omon + fgo2, fgco2, fgco2abio, fgco2nat, tos, sos, hfds. Using hist-bgc would eventually probably be better but there is little output available presently. I only think 1 version of each unique ocean model and 1 ensemble member are needed.
Anticipated Software Tools
Jupyterhub, Python, xarray and/or R
What software libraries do you intend to use? Will your project involve developing new software?
Anyone interested in seasonal air-sea exchange of O2 and CO2. It may be possible to team up with one of the other projects evaluating ocean carbon and oxygen.