Fine-scale spatial and temporal variability of surface water dimethylsufide (DMS) concentrations and sea–air fluxes in the NE Subarctic Pacific

We report the results of a 2 year (6 cruises) survey of surface water dimethylsulfide (DMS) concentrations in the Subarctic Pacific Ocean using membrane inlet mass spectrometry for high spatial resolution measurements. Our results document strong variability in surface water DMS concentrations along a repeated coastal–oceanic transect. DMS concentrations were consistently low (~ 1–2 nM) in February, and increased to summertime mean values of ~ 8 nM. For both survey years, we observed higher DMS concentrations in near shore waters during early summer (June), but a reversal of this spatial gradient in August when the highest DMS concentrations were observed in open ocean regions. Sea–air DMS fluxes ranged from ~ 5 to 25 μmol m− 2 day− 1 and did not show the consistent spatial and temporal patterns observed for surface water concentrations. Fine-scale spatial variability was present for both surface water concentrations and sea–air fluxes. Some of this variability could be attributed to underlying physical and biologically heterogeneity, including the presence of localized phytoplankton blooms at the coastal–oceanic transition boundary. Using a simple statistical approach, we estimate that the mean length scale of DMS variability along our sampling transects was < 10 km, which was significantly shorter than that observed for physical variables (temperature and salinity), but somewhat larger than the variability length scale of chlorophyll a (chla). Using multiple linear regression analysis, we were unable to produce a single consistent empirical relationship predicting surface DMS concentrations from a suite of biological and hydrographic variables. However, DMS did show significant correlations with some variables including calcite, chlorophyll a and mixed layer depth (MLD). Mean DMS concentrations across cruises were related to chla/MLD ratios and the solar radiation dose, in a manner that was consistent with previously published algorithms. However, these algorithms failed to predict the mesoscale and sub-mesoscale variability along the cruise track. High frequency measurements of DMS during an extended occupation of Ocean Station Papa demonstrated large variability over periods ranging from ~ 12 to > 24 h. This variability could not be explained by simple empirical analysis, but showed some correspondence with daily cycles of incoming solar irradiance. Simple calculations suggest that biological turnover was likely a significant source of temporal variability in DMS concentrations at Ocean Station P. Our observations demonstrate the importance of high-resolution measurement techniques in furthering our understanding of ocean DMS dynamics.

Research highlights
► DMS measurements in the NE Subarctic Pacific show unprecedented spatial and temporal variability.
► Fine-scale variability is contrasted with that of underlying physical and biological fields.
► Global empirical algorithms explain seasonal trends but not mesoscale variability.
► Measurements resolve rapid temporal dynamics of surface water DMS concentrations.