An ocean surface paradox: gas equilibrium with atmosphere

Marine science tells us that the surface of Earth’s oceans is in gaseous equilibrium with its atmosphere (Yingxu Wu et al 2022). In the case of the key atmospheric trace gas CO₂, the partition across the phase boundary is given by Henry constants as established by Li and Tsui 1971 and by Weiss 1974, while outside the laboratory there are extensive datasets for the atmospheric mol fraction (ppm CO₂) embodied in the familiar `Keeling curves’, as measured at oceanic, polar and continental locations (Yuan et al 2019).

Sea surface temperatures are widely available for Earth’s oceans (Kent and Kennedy 2021). We have therefore interpreted the Henry Constants from Li and Tsui (1971) and from Weiss (1974) as headspace mol fractions (ppm CO₂) against temperature, and added representative field data from Mauna Loa (https://gml.noaa.gov/ccgg/trends/).

A disparity is evident, which we address as follows: In case the well-known differential between the two 1970s laboratory curves is somehow attributable to pre-treatment including acid in both cases and a biocide in one, we speculate that the outcomes of both might be different if the seawater samples had been treated as biological fluids.

Expanding therefore our studies of atmospheric gas partitioning at a growing ice surface reported to recent EGU conferences, and building on valued conversations with colleagues at EGU 2022, we will present provisional results from gas equilibration in the headspace above freshly-collected (≈`live’) seawater from UK’s Atlantic coast.