Abstract
AbstractWe have developed a statistical gap‐filling method adapted to the specific coverage and properties of observed fugacity of surface ocean CO2 (fCO2). We have used this method to interpolate the Surface Ocean CO2 Atlas (SOCAT) v2 database on a 2.5°×2.5° global grid (south of 70°N) for 1985–2011 at monthly resolution. The method combines a spatial interpolation based on a “radius of influence” to determine nearby similar fCO2 values with temporal harmonic and cubic spline curve‐fitting, and also fits long‐term trends and seasonal cycles. Interannual variability is established using deviations of observations from the fitted trends and seasonal cycles. An uncertainty is computed for all interpolated values based on the spatial and temporal range of the interpolation. Tests of the method using model data show that it performs as well as or better than previous regional interpolation methods, but in addition it provides a near‐global and interannual coverage.
Highlights
IntroductionThe world’s oceans absorb approximately 25% of the total anthropogenic emissions of carbon dioxide (CO2) released into the atmosphere every year [MikalofFletcher et al, 2006; Le Quere et al, 2009]
The gap-filling method allows us to produce monthly fugacity of surface ocean CO2 (fCO2) values for the years 1985–2011 on a 2.5832.58 grid south of 708N based on the Surface Ocean CO2 Atlas (SOCAT) v2 database
One exception to this is the Southern Ocean in the Antarctic Circumpolar Current, where strong zonal currents result in very similar fCO2 in neighboring grid cells
Summary
The world’s oceans absorb approximately 25% of the total anthropogenic emissions of carbon dioxide (CO2) released into the atmosphere every year [MikalofFletcher et al, 2006; Le Quere et al, 2009]. The air-sea fluxes are driven primarily by the difference in the concentration of CO2 between the atmosphere and the ocean surface. Over 10 million surface ocean fCO2 measurements have been collected since 1968 [Takahashi and Sutherland, 2013; Pfeil et al, 2013; Bakker et al, 2014]. The majority of these measurements have been obtained in the northern hemisphere (Figure 1a) during the past 20 years (Figure 1b), which restricts in-depth analysis of global patterns and long-term trends
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