Liu, Yina (2013-08). Global Distributions and Natural Sources of Brominated very Short-Lived Substances. Doctoral Dissertation. | Thesis individual record

Brominated very short-lived substances (BrVSLS) are atmospherically important trace gases that play an important role in stratospheric ozone destruction. Major BrVSLS including bromoform (CHBr_(3)), dibromomethane (CH_(2)Br_(2)), chlorodibromomethane (CHClBr_(2)), and bromodichloromethane (CHBrCl_(2)) are thought to be predominately formed naturally via vanadium bromoperoxidase (V-BrPO) mediated halogenation of organic matter (OM). The objective of this research was to couple field observations and laboratory experiments to understand global distributions, saturation anomalies, fluxes, and identify natural sources of BrVSLS. All the trace gases were measured with gas chromatography mass spectrometry (GC-MS).

Field observations were conducted in the Pacific and Atlantic Oceans. Results from field observations showed that BrVSLS tend to be elevated in biologically active waters, such as coastal waters, the productive surface open ocean, and at chlorophyll maximum depths. The production of natural BrVSLS is likely controlled by complex biogeochemical factors in the ecosystems. CH_(2)Br_(2) was thought to be derived from the same source(s) as CHBr_(3), but results presented in this dissertation suggest they may in fact be derived from disparate sources.

Screening for important BrVSLS producers was attempted in the laboratory. Only 2 out of 9 phytoplankton species screened show observable BrVSLS production. CH_(2)Br_(2) production was only observed in 1 species screened. Chloroperoxidase-like activity in diatom was observed for the first time, which provided evidence for biological production of chloroform (CHCl_(3)).

The role of dissolved organic matter (DOM) in controlling BrVSLS production was investigated in the laboratory. Production of BrVSLS varied significantly with different model DOM compounds upon V-BrPO mediated halogenation. Certain DOM enhanced BrVSLS production, but the majority of the model DOM compounds tested in this study either interfered with or had no observable effect on BrVSLS production. Further evidences showed that V-BrPO mediated halogenation can alter DOM chemical characteristics. Alteration of colored dissolved organic matter (CDOM) in terms of "bio-bleaching" was observed in model lignin phenol compounds and CDOM collected from two cyanobacterial cultures.

Results from this study suggest that the presence of V-BrPO producing phytoplankton is essential for enhanced BrVSLS production, as V-BrPO induced brominated reactive species, such as hypobromous acid (HOBrenz), is required. However, BrVSLS production rates are largely controlled by other biogeochemical factors in seawater, such as DOM composition. Results from this study also suggest that V-BrPO activity not only plays an essential role in BrVSLS production, but it also plays a significant role in the transformation of DOM and may be a significant component of the marine carbon cycle.

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