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UBC Theses and Dissertations

Distribution and dynamics of biogenic sulfur in the northeast Subarctic Pacific : insights from new and refined analytical techniques Herr, Alysia Elizabeth


The northeast subarctic Pacific (NESAP) is a globally important source of the climate-active gas dimethylsulfide (DMS), yet the processes driving DMS variability across this region are poorly understood. This thesis aims to provide insight into the distribution and cycling of DMS and related sulfur compounds dimethylsulfoxide (DMSO) and dimethylsulfoniopropionate (DMSP) by examining new concentration data, together with biological cycling rates and related oceanographic variables. Chapter 2 examines the distribution of DMS at various spatial scales across contrasting oceanographic regimes of the NESAP. We present a new data set of high spatial resolution DMS measurements across hydrographic frontal zones, together with key environmental variables and biological rate measurements. We combine these new data with existing observations to produce a revised summertime DMS climatology for the NESAP. Our results suggest the presence of two distinct DMS cycling regimes corresponding to microphytoplankton-dominated waters along the continental shelf, and nanoplankton-dominated transitional waters. In all areas, DMS consumption appeared to be an important control on concentration gradients, with higher DMS consumption rate constants associated with lower DMS concentrations. Based on our compiled observations, we estimated that this region emits 0.30 Tg of sulfur to the atmosphere during the summer season. Chapter 3 presents results from two cruises examining DMSO distributions and cycling across the NESAP. We measured DMSO concentrations and turnover rates across a range of hydrographic regions, and quantified rates of DMSO reduction, DMSP cleavage and DMS oxidation. Our results show high concentrations and rapid turnover rates of DMSO across the NESAP. Across our survey, DMSO reduction exceeded DMSPd cleavage at nearly all stations, while the rates of DMSO reduction exceeded those of DMS oxidation at four stations where both these rates were measured. These results suggest that DMSO reduction was an important net source of DMS. A Lagrangian survey showed a significant decrease in DMSO concentrations during periods of peak irradiance, in conjunction with markers of oxidative stress. Our findings highlight the significant contribution of DMSO to DMS production in the NESAP, and its potential physiological importance as an anti-oxidant in phytoplankton assemblages.

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