Other
Scientific paper
Mar 1989
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1989gecoa..53..699r&link_type=abstract
Geochimica et Cosmochimica Acta, vol. 53, Issue 3, pp.699-707
Other
4
Scientific paper
The quantitative distributions of loliolide and the major phytoplankton carotenoids: fucoxanthin, diadinochrome, diatoxanthin, and -carotene in two cores of anoxic marine sediment recovered from the Peru continental shelf are reported. Our results demonstrate that the rapid degradation of carotenoids in sediments is not a result of their high degree of unsaturation as has been previously suggested. Instead, carotenoids exhibit a wide range of degradation rates that are proportional to the ability of specific pigments to form unstable bicyclic furanoxides. Carotenoid furanoxides undergo subsequent fragmentation to loliolide, isololiolide, dihydroactinidiolide and other, as yet undetermined, low molecular weight products. This degradation pathway accounts for the relative rates of removal for specific carotenoids (fucoxanthin = fucoxanthinol > diadinoxanthin > DIATOXANTHIN = carotene), the distribution of carotenoids reported by Wpatts and Maxwell (1977) and C et al . (1978) in ancient sediments, the occurrence of novel carotenoid transformation products in surface sediments reported by r pidout et al . (1984), and the distribution of loliolides in recent sediments recovered from the Namibian shelf reported by k plok et al . (1984a,b). We predict that loliolide and isololiolide will inherit a specific stereochemistry from their carotenoid precursors, but that dihydroactinidiolide will be racemic. For every mole of fucoxanthin degraded in Peru sediments, 0.7-1.1 mole of loliolide is produced. Summation of fucoxanthin and loliolide at each subsurface horizon yields an estimate of the total deposition of fucoxanthin at t = 0. Throughout the 0-20 cm depth of our samples, this parameter is remarkably constant to ±16%. Individual horizons exhibit excursions which may reflect changes in surface productivity. Extrapolation of our measurements to deeper sediments may therefore be of some value in deciphering questions on environmental conditions of deposition and paleoproductivity.
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