Novel unsaturated straight-chain C37C39 methyl and ethyl ketones in marine sediments and a coccolithophore Emiliania huxleyi

Abstract Novel, very long (C 37 C 39 ) straight-chain ketones have been identified in a range of marine sediments varying in age from very Recent to Miocene. The ketones are separable by thin-layer chromatography into methyl ketones and ethyl ketones, and within each group only diunsaturated and triunsaturated ketones are present. Relative to other lipid classes present, concentrations are high in Plio-Pleistocene and Miocene Japan Trench sediments (38–720 ng/g), and in very Recent Walvis Bay (1200–2100 ng/g) and northern North Sea sediments (650 ng/g). Identical compounds have been identified in the marine coccolithophore Emiliania huxleyi and with the exception that triunsaturated ketones are more abundant in this alga, the distributions are quite similar to those of the sediments. Studies involving feeding of E. huxleyi to the copepod Calanus helgolandicus indicate that the copepod assimilates only a small proportion of the ketones, most of which are excreted in the faecal pellets. This is not simply due to excretion of whole algal cells, but due to the apparent inability of the copepod to digest these compounds. This resistance to biological degradation may explain the high abundances observed in some sediments.