Decreased marine dimethyl sulfide production under elevated CO2 levels in mesocosm and in vitro studies

The oceans have absorbed approximately half of the CO2 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 CaCO3 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 CO2 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.