The Chemistry and Climatic Role of Biogenic Sulfur: Group Discussion

Abstract

Discussions centred on the behaviour of dimethyl sulfide (DMS), the most abundant volatile sulfur compound detectable in sea-water, and its primary end oxidation products methyl sulphonic acid (MSA) and sulfate. MSA is believed to be exclusively derived from MSA and therefore is potentially an important tracer for biogenic sulfate productivity. The ratio of MSA/nss sulfate in particular has been proposed [Saltzman, this volume] as a tracer for the origin of sulfate in marine air masses and in subsequent snowfall deposits, MSA has therefore become a target for ice-core studies aimed to detect either a response in the sulfur cycle to a climate shift, or evidence for possible climate forcing by sulfate aerosol. However, due to the inhomogeneous global distribution of DMS producing phytoplankton, combined with uncertainty about their likely climate sensitivity, the spatial pattern of emissions is still poorly known. Signals detected in ice cores are therefore a complex integral of a variety of processes affecting not only the emission rates at source, but also the pathways and efficiencies involved during transport and deposition onto the ice sheets, In addition, sub-annual changes recorded in the ice may be affected by limited post-depositional migration within the snowpack which has been reported at several near-coastal Antarctic sites.