Occurrence of novel monocyclic alkenes from diatoms in marine particulate matter and sediments

Widely occurring alkenes reported in sediments from around the globe, but which previously had unknown identities and sources, have now been assigned. They include a novel monocyclic C25 triene and novel C30 monocyclic tetra- and pentaenes. Recently, these compounds have been shown to be biosynthesised by some strains of the widespread planktonic diatom, Rhizosolenia setigera, and this appears to be the likely source of the alkenes in the marine environment. The hydrocarbons were identified by comparison of the gas chromatographic retention data and mass spectra of the sedimentary alkenes isolated from the Arabian Sea, Peru upwelling region and Cariaco Trench with data for the pure isolated alkenes from R. setigera. The compounds co-occur with well-known diatomaceous Δ7(20) highly branched isoprenoid haslenes and rhizenes in all of these environments but were absent from sediments from the Black Sea, even though Δ5 haslenes were abundant in the latter sediments. These differences possibly reflect the different diatom species contributing alkene lipids to each sedimentary environment. The newly identified compounds may be further useful biological markers of diatom inputs to sediments.