Alkenone

Alkenones are long-chain unsaturated methyl and ethyl n-ketones produced by a few phytoplankton species of the class Prymnesiophyceae. Alkenones have been observed containing between 35 and 41 carbon atoms and with between one and four double bonds. Uniquely for biolipids, alkenones have a spacing of five methylene groups between double bonds, which are of the less common E configuration. The biological function of alkenones remains under debate although it is likely that they are storage lipids. Alkenones were first described in ocean sediments recovered from Walvis Ridge and then shortly afterwards in cultures of the marine coccolithophore Emiliania huxleyi. The earliest known occurrence of alkenones is during the Aptian 120 million years ago. They are used in organic geochemistry as a proxy for past sea surface temperature.