Abstract
Abstract. Climatologies, or long-term averages, of essential climate variables are useful for evaluating models and providing a baseline for studying anomalies. 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 fugacity, fCO2. As fCO2 is highly sensitive to temperature, the measurements are only valid for the instantaneous sea surface temperature (SST) that is measured concurrently with the in-water CO2 measurement. To create a climatology of fCO2 data suitable for calculating air–sea CO2 fluxes, it is therefore desirable to calculate fCO2 valid for a more consistent and averaged SST. This paper presents the OceanFlux Greenhouse Gases methodology for creating such a climatology. We recomputed SOCAT's fCO2 values for their respective measurement month and year using monthly composite SST data on a 1° × 1° grid from satellite Earth observation and then extrapolated the resulting fCO2 values to reference year 2010. The data were then spatially interpolated onto a 1° × 1° grid of the global oceans to produce 12 monthly fCO2 distributions for 2010, including the prediction errors of fCO2 produced by the spatial interpolation technique. The partial pressure of CO2 (pCO2) is also provided for those who prefer to use pCO2. The CO2 concentration difference between ocean and atmosphere is the thermodynamic driving force of the air–sea CO2 flux, and hence the presented fCO2 distributions can be used in air–sea gas flux calculations together with climatologies of other climate variables.
Highlights
1.1 IntroductionObservations demonstrate that dissolved CO2 concentrations in the surface ocean have been increasing nearly everywhere, roughly following the atmospheric CO2 increase but with large regional and temporal variability (Takahashi et al, 2009; McKinley et al, 2011)
If we use the standard deviation of the kriging as an estimate of the prediction error, the prediction error of fCO2,cl in a single grid cell ranged between ∼ 6 and ∼ 50 μatm and was ∼ 20 μatm average
The fCO2 predictions and standard deviations are computed for the year 2010 and interpolated to a global 1◦ × 1◦ grid, and have been made available together with other climatological data necessary to calculate global oceanic CO2 fluxes
Summary
Observations demonstrate that dissolved CO2 concentrations in the surface ocean have been increasing nearly everywhere, roughly following the atmospheric CO2 increase but with large regional and temporal variability (Takahashi et al, 2009; McKinley et al, 2011). Accurate knowledge of air–sea fluxes of heat, gas and momentum is essential for assessing the ocean’s role in climate variability, understanding climate dynamics, and forcing ocean/atmosphere models for predictions from days to centuries (Wanninkhof et al, 2009). The project has developed data sets suitable for computation of gas flux climatology in which mean gridded values are computed from multiple measurements over different years.
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