Interpolation of TCO2 Below the Deepest Mixed Layer
As shown earlier (Goyet and Davis 1997), below the winter mixed layer, TCO2 can be interpolated as a function of potential temperature (), apparent oxygen utilization (AOU), and salinity (S):
TCO2 = a + bθ + cAOU + dS (2)
The coefficients were calculated for each profile, interpolated to the 3-D grid using the GMT software, and applied to climatological hydrographic properties to compute TCO2 at the grid points below the deepest winter mixed layer depth. Uncertainty associated with this interpolation procedure in the Indian, Pacific, and Atlantic Oceans is respectively estimated to be ±7.9 µmol/kg, ±14.5 µmol/kg, and ±8.1 µmol/kg. The mean uncertainty associated with the TCO2 interpolation procedure in the global ocean below the mixed layer is estimated to be ±9.4 µmol/kg. The uncertainty is the largest in the Pacific Ocean and reflects the relatively poor data density in this large ocean.