| Summary: | A wide range of trace gases, including dimethyl sulphide (DMS) and organohalogens, are formed in the surface oceans via biological and/or photochemical processes. Consequently, these gases become supersaturated in seawater relative to the overlying marine air, leading to a net flux to the atmosphere. Upon entering the atmosphere, they are subject to rapid oxidation or radical attack to produce highly reactive radical species which are involved in a number of important atmospheric and climatic processes. Organohalogens can affect the oxidizing capacity of the atmosphere by interacting with ozone, with implications for air quality, stratospheric ozone levels, and global radiative forcing. DMS and iodine-containing organohalogens (iodocarbons) can both contribute to direct and indirect impacts of aerosols on climate through the production of new particles and cloud condensation nuclei (CCN) in the clean marine atmosphere. Therefore, marine trace gases are considered a vital component of the earth’s climate system, and changes in the net production rate and subsequent sea-to-air flux could have an impact on globally important processes. In recent years, attention has turned to the impact that future ocean acidification may have on the production of such gases, with the greatest focus on DMS and organohalogens. In this chapter, the current state-of-the-art in this growing area of research is outlined. The oceans are a major source of sulphur (S), an element essential to all life, and marine emissions of the gas DMS (chemical formula (CH3)2S) represent a key pathway in the global biogeochemical sulphur cycle. The surface oceans are supersaturated with DMS relative to the atmosphere, resulting in a oneway flux from sea to air (Lovelock et al. 1972; Watson and Liss 1998). DMS is a breakdown product of the biogenically produced dimethyl sulphoniopropionate (DMSP): . . . (CH3)2S+CH2CH2COO- → (CH3)2S + CH2CHCOOH (acrylic acid) (11.1) . . . Single-celled marine phytoplankton are the chief producers of DMSP, and this ...
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