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.