Oxygenated volatile organic chemicals in the oceans: Inferences and implications based on atmospheric observations and air-sea exchange models

Abstract

Airborne measurements of oxygenated volatile organic chemicals (OVOC), OH free radicals, and tracers of pollution were performed over the Pacific during Winter/Spring of 2001. We interpret atmospheric observations of acetaldehyde, propanal, methanol, and acetone with the help of a global 3-D model and an air-sea exchange model to assess their oceanic budgets. We infer that surface waters of the Pacific are greatly supersaturated with acetaldehyde and propanal. Bulk surface seawater concentration of 7 nM (10−9 mol L−1) and 2 nM and net fluxes of 1.1 × 10−12 g cm−2 s−1 and 0.4 × 10−12 g cm−2 s−1 are calculated for acetaldehyde and propanal, respectively. Large surface seawater concentrations are also estimated for methanol (100 nM) and acetone (10 nM) corresponding to an under-saturation of 6% and 14%, and a deposition velocity of 0.08 cm s−1 and 0.10 cm s−1, respectively. These data imply a large oceanic source for acetaldehyde and propanal, and a modest sink for methanol and acetone. Assuming a 50–100 meter mixed layer, an extremely large oceanic reservoir of OVOC, exceeding the atmospheric reservoir by an order of magnitude, can be inferred to be present. Available seawater data are both preliminary and extremely limited but indicate rather low bulk OVOC concentrations and provide no support for the existence of a large oceanic reservoir. We speculate on the causes and implications of these findings.