The gradients in partial pressure of CO2 across the air–sea interface provide a starting point for estimating regional and global CO2 fluxes between the atmosphere and ocean. They also are critical constraints on global atmospheric and oceanic models used to infer the land–sea partitioning of CO2 uptake. Here, we assess the factors that contribute to uncertainties in the estimated CO2 fluxes.
We estimate measurement precision in pCO2 to be ±2 μatm, and extrapolation of the data to regions with no measurements yields uncertainties of ±0.8 μatm. The short duration of spring blooms in the North Atlantic diminishes the uncertainties arising from sparse seasonal coverage in the measurements. We estimate an oceanic uptake of 0.3 Gt C/yr due to spring blooms in the North Atlantic. It is difficult to quantify the extent to which pCO2 gradients may change by correcting the pCO2 measurements to skin instead of bulk temperatures, as skin–bulk temperature differences may be positive (negative) with strong surface heating (cooling), or may vanish under high wind conditions. Uncertainties in fluxes associated with gas exchange rates cannot be separated from the yet unknown flux contributions from the covariance between high-frequency wind and pCO2 fluctuations.
In addition to expanded spatial coverage, high-resolution and high-frequency sampling of the meteorology, hydrography, and carbon system in the atmospheric and oceanic boundary layers at a few locations is needed for improving estimates of air-sea CO2 fluxes.