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UBC Theses and Dissertations

Membrane inlet mass spectrometry (M(MS) : a novel approach to the oceanic measurement of dimethylsulfide Nemcek, Nina


A novel technique, membrane inlet mass spectrometry (MIMS), was used to measure dimethylsulfide gas (DMS) and algal dimethylsulfoniopropionate (DMSPp) concentrations in two different marine ecosystems of the NE Pacific. In oceanic waters along Line P, DMS levels had been observed to be unusually high, yet particulate DMSP levels had not been extensively measured. DMSPp concentrations during 3 consecutive spring cruises ranged from 0.2-63.2 nM (mean 21.5 nM , s.d. 15.0 nM ) in the upper 50 m of the water column, and varied significantly with depth, across stations and between study years. DMSPp generally decreased with depth and distance from the coast. DMSPp concentrations at most stations in 2003 were 2 to 3-fold higher than in subsequent years, and were significantly correlated to the biomass of dinoflagellates (r2 = 0.46) across the survey region. Although phytoplankton biomass (chlorophyll a) also declined in 2004-2005, DMSPp:chl ratios did as well, indicating a physiological or taxonomic change in the phytoplankton community. Surface DMS concentrations were measured underway along with pCO₂, O₂/Ar, temperature, salinity and chlorophyll a in productive, coastal waters off British Columbia. All parameters exhibited large ranges, (pCO₂, 200-747 ppm; DMS, <l-28.7 nM; chl a, <0.1-33.2 μg L⁻¹), highlighting the dynamic nature of the region. A tight anti-correlation between pC0₂ and O₂/Ar was observed across the region (r = 0.90), with the distributions of these gases strongly influenced by both biological (photosynthesis and respiration) and physical (upwelling) processes. In contrast, DMS levels which exhibited rapid, fine-scale fluctuations irresolvable with traditional methods, were unrelated to any single variable. A significant linear relationship although with a different scaling factor to that derived from open ocean data. Lower resolution was however observed between DMS and the chlorophyll to mixed layer depth ratio (r² = 0.83), sampling in this region can introduce errors as large as 41% o f the mean concentration for DMS, emphasizing the utility of MHVIS in dynamic areas. In conclusion, MIMS proved to be a significant advance for DMS measurement, yet improvements need to be made for it to be a viable alternative to other methods for DMSP measurements.

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