| Summary: | Dimethyl sulfide (DMS) is a trace gas produced in the ocean that plays an important role in climate and contributes to the Earths energy balance. DMS is a product of the enzymatic cleavage of dimethyl sulfoniopropionate (DMSP), which is produced by certain phytoplankton species and bacteria. Processes within the DMS/P cycles in the surface ocean are complex and vary with time and space. In the sea surface microlayer (SML), which is the interface between the ocean and the atmosphere, DMS concentration may be altered relative to subsurface water (SSW), by elevated biological activity, light intensity, and gas exchange. The aim of this thesis is to determine the importance of the SML in DMS/P dynamics and air-sea exchange by developing a more robust technique for SML sampling to better understand the dynamics of DMSP and DMS, and comparing their dynamics in the SML and SSW in coastal waters and the open ocean. In addition, the impact of warming and ocean acidification on DMS/P dynamics is investigated to determine how they will be impacted by future climate change. To characterize DMS dynamics in the SML, a more effective method for sampling trace gases in the SML was developed (Chapter 2). The method is reliant on diffusion through a gas-permeable tube due to the concentration gradient. The floating tube was tested and calibrated under semi-controlled conditions using coastal water, where its reproducibility, accuracy and effectiveness were established. The potential benefits of this new technique for sampling trace gases in the SML include reduced loss of DMS to air. The higher reproducibility and accuracy compared to other techniques confirmed the potential of the floating tube technique for trace gas measurement in the SML. The method developed in Chapter 2 was applied in sampling of DMS in the SML along a coastal-open ocean gradient (Chapter 3), and in various water masses of the open ocean (Chapter 4). In both chapters, DMSP and DMS dynamics were related to biological, biogeochemical, and physical properties ...
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