Abstract. We present air-sea fluxes of oxygenated volatile organics compounds (OVOCs) quantified by eddy covariance (EC) during the Atlantic Meridional Transect cruise in 2012. Measurements of acetone, acetaldehyde, and methanol in air as well as in water were made in several different oceanic provinces and over a wide range of wind speeds (1-18 m s −1 ). The ocean appears to be a net sink for acetone in the higher latitudes of the North Atlantic but a source in the subtropics. In the South Atlantic, seawater acetone was near saturation relative to the atmosphere, resulting in essentially zero net flux. For acetaldehyde, the two-layer model predicts a small oceanic emission, which was not well resolved by the EC method. Chemical enhancement of air-sea acetaldehyde exchange due to aqueous hydration appears to be minor. The deposition velocity of methanol correlates linearly with the transfer velocity of sensible heat, confirming predominant airside control. We examine the relationships between the OVOC concentrations in air as well as in water, and quantify the gross emission and deposition fluxes of these gases.

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Environmental context. As atmospheric CO 2 levels rise due to human activities, more of the gas dissolves in the oceans, increasing their acidity. The effect of these seawater changes on marine organisms is largely unknown. We examine the consequences of higher CO 2 levels on the production by plankton of dimethyl sulfide, a climatically active gas. We find that higher CO 2 levels leads to lower concentrations of dimethyl sulfide in the seawater, which has potentially important implications for the future climate.Abstract. The oceans have absorbed approximately half of the CO 2 produced by human activities and it is inevitable that surface seawaters will become increasingly acidified. The effect of lower pH on marine organisms and ocean-atmosphere exchanges is largely unknown but organisms with CaCO 3 structural components are likely to be particularly affected. Because calcifying phytoplankton are significant producers of dimethyl sulfide (DMS), it is vital to understand how lower seawater pH may affect DMS production and emission to the atmosphere. Here we show, by mesocosm (Raunefjorden, Norway, April-May 2003) and in vitro studies, that the net production of DMS and its cellular precursor dimethylsulfoniopropionate (DMSP) is approximately halved in microbial communities subjected to doubled CO 2 levels. Our findings provide evidence that the amount of DMS entering the atmosphere could decrease in the future. Because atmospheric oxidation of DMS can lead to climate cooling by increasing cloud albedo, a consequence of reduced DMS emissions from a lower pH ocean would be an enhancement in global warming.

Abstract. We present air–sea fluxes of oxygenated volatile organics compounds (OVOCs) quantified by eddy covariance during the Atlantic Meridional Transect cruise in 2012. Measurements of acetone, acetaldehyde, and methanol were made in several different oceanic provinces and over a wide range of wind speeds of 1–18 m s−1. The ocean appears to be a sink for acetone in the higher latitudes of the North Atlantic but a source in the subtropics. In the South Atlantic, seawater acetone was near saturation relative to the atmosphere, resulting in essentially zero net flux. For acetaldehyde, a small oceanic emission is implied from measured flux, but of a lower magnitude than predicted based on the two-layer model. Chemical enhancement of air–sea acetaldehyde exchange due to aqueous hydration appears to be minor. The deposition velocity of methanol correlates linearly with the transfer velocity of sensible heat, confirming predominant airside control. We examine the relationships between the OVOC concentrations in air as well as in water, and compute the gross emission and deposition fluxes of these gases.