DMS/P/O dynamics in the Subarctic Pacific: Insights from autonomous sensors and isotope tracer studies

The Subarctic Pacific Ocean is a global hot-spot for the production and cycling of the climate-active gas dimethyl sulfide (DMS), and the related compounds Dimethyl sulfoniopropionate (DMSP) and dimethyl sulfoxide (DMSO). At present, the underlying causes for high DMS/P/O concentrations in the Subarctic Pacific are not fully known, although several factors have been suggested, including the abundance of high DMSP-producing coccolithophores, iron limitation, and strong salinity-based mixed layer stratification. Here we present new field results examining the cycling of DMS, DMSP and DMSO across contrasting hydrographic regimes in the Subarctic Pacific. Using membrane inlet mass spectrometry, and the automated Organic Sulfur Chemical Analysis Robot (OSCAR), we assessed the fine-scale variability in these compounds in offshore and coastal waters. Our results demonstrate strong gradients in DMS/P concentrations across hydrographic frontal zones, and regional coherence with physical variables including salinity, sea-surface height and oxygen concentrations in depth profiles. Process studies, using a stable isotope tracer technique demonstrate rapid inter-conversion between DMS/P/O, with particular high rates of net DMSO reduction to DMS. These latter results indicate that DMSO may be a more important source of DMSO production than previously believed. Our results have implications for understanding the dynamics of DMS/P/O under shifting oceanic conditions.