The derivation of a CO2 Fugacity Climatology from SOCATís Global in Situ Data
Goddijn-Murphy, Lonneke1; Woolf, David2; Land, Peter3; Shutler, Jamie3
1Environmental Research Institute, NHC-UHI, UNITED KINGDOM; 2International Centre for Island Technology, Heriot Watt University, UNITED KINGDOM; 3Plymouth Marine Laboratory, UNITED KINGDOM

In the Oceanflux Greenhouse Gases project, Earth Observation, in situ and model data are combined to obtain a climatology of key parameters that can be used to determine atmosphere-ocean CO2 fluxes. A main goal is to produce a monthly 1° x 1° global climatology data. Since the CO2 concentration difference between ocean and atmosphere is the thermodynamic driving force of the CO2 flux, one of the scientific challenges concerns the estimation of oceanic CO2 concentration. This CO2 concentration is related to the partial pressure (pCO2) or fugacity (fCO2). The Surface Ocean CO2 Atlas (SOCAT) has made millions of global underway sea surface measurements of CO2 publicly available, all in a uniform format and presented as fCO2. However, these fCO2 values are valid strictly only for the instantaneous temperature at measurement and are not ideal for climatology. We recomputed these fCO2 values to be applicable to monthly averages of SST on a 1° x 1° grid derived from the Advanced Along-Track Scanning Radiometer (AATSR) Re-processing for Climate (ARC) Dataset of Sea Surface Temperature Retrievals. Concentrations for the measurement month can then be calculated using a solubility calculated from the climatological temperature and salinity. Concentrations in a reference year are calculated by applying an assumed secular trend and then using a solubility appropriate to the reference year. We detail the methodology for calculating ''climatological'' CO2 concentrations from SOCAT values and climatological estimates of temperature.