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UBC Theses and Dissertations

Contrasting distributions and cycling of reduced sulfur compounds in saline and estuarine waters of the coastal NE subarctic Pacific Zheng, Zhiyin

Abstract

The trace gas dimethylsulfide (DMS) is considered to be one of the most important sulfur compounds in the marine environment. Research on this volatile sulfur compound has been stimulated by its potential role in regulating regional and global climate, and its importance, along with the related sulfur compounds, dimethylsulfoniopropionate (DMSP) and dimethylsulfoxide (DMSO), as carbon and sulfur sources for microbes in the marine environment. The northeast subarctic Pacific (NESAP) is one of the global DMS hotspots, with significant spatial and temporal variability in DMS production. The difference in nutrient supply between coastal and offshore waters in this region drives significant variability in phytoplankton community structure, primary productivity, and thus sulfur cycling. The goal of this thesis is to characterize the patterns of sulfur cycling in two hydrographically distinct regimes in the NESAP, and to provide insights into the relative contribution of various DMS production pathways. Chapter 2 presents new measurements of DMS, DMSP and DMSO (DMS/P/O) concentrations and turnover rate constants made in the coastal NESAP, as well as ancillary hydrographic and satellite data that help explain the underlying factors influencing DMS/P/O distributions and cycling. A strong linear relationship was demonstrated between DMS and DMSO concentrations, confirming similar ratios found in previous studies. Turnover rate constants for net DMS production from DMSO were comparable to those for DMSP, indicating DMSO reduction as an important pathway for marine DMS production. Similar rate constants for DMSP cleavage and DMSO reduction between the two regimes were found, although the lower average of kDMSPcleav in the continental shelf waters may indicate higher bacterial sulfur demand in the more productive shelf waters. Our findings provide insights into marine sulfur dynamics in adjacent but contrasting marine waters, and highlight the significant contribution of DMSO to DMS production. This result suggests a need for improved understanding of marine DMSO cycling. In addition to the main research presented in the body of this thesis, the Appendices present supplementary tests of various DMSP preservation methods, and a detailed protocol for DMSO reduction by the TiCl3 method. These methodological details will be useful for future sulfur studies.

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