Marine algae and DMS

Marine algae are able to cope with salty conditions by the production of dimethylsulphonio proprionate (DMSP). This substance is electrically neutral, carrying a positive charge associated with sulphur, and a negative charge associated with the propionic acid ion, on the same molecule. The internal neutralization of its ionic charges renders it non-toxic, and cells that are able to substitute a large proportion of betaine for salt are able to reduce the osmotic pressure between the cell interior and the external sea water. (see variation 22)

The sulphur cycle

When marine algae die or are eaten, the sulphur betaine decomposes easily to yield the acrylic acid ion and dimethyl sulphide (DMS). Onshore breezes carry the dimethyl sulphide inland where atmospheric gases decompose it into a non-sea salt sulphate aerosol comprised of sulphate and methane sulphonate. In this form sulphur is deposited on the ground, thereby enhancing the growth of land plants, and also increasing the rate ot rock weathering. The increased flow of nutrients to the oceans is of obvious benefit to marine organisms, and so the sulphur cycle is perceived as mutually beneficial to both land- and sea-based ecosystems.