Carotenoid diagenesis in a marine sediment

The major carotenoids at three levels (3, 40 and 175 m below the sediment-water interface) in a core from a marine sediment (Cariaco Trench, off Venezuela) have been examined. Mass and electronic spectral data have provided evidence for the onset of a progressive reduction of carotenoids in the geological column. The time scale of the process appears to depend on the particular carotenoid. Reduction of up to two double bonds is observed for the diol, zeaxanthin, in the oldest sediment (ca. 340,000 yr B.P.) but no reduction is observed in the younger samples (ca. 5000 and ca. 56,000 yr B.P.). The diketone, canthaxanthin, shows evidence of reduction of up to two double bonds in the 56,000 yr sample and of up to five double bonds in the oldest sample. No reduction of β-carotene was observed in any of the samples.