Are Carotenol-Chlorin Esters Diatom Biomarkers?

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Novel esters of carotenols and chlorins (Carotenol-Chlorin-Esters, CCEs) were recently discovered by the investigator in sediments from the Oman and Peru margin, the Southern California Bight, and Monterey Bay. The chlorins associated with CCEs were pheophorbide a and pyropheophorbide a, degradation products of chlorophyll a (Chl a). Isofucoxanthin-dehydrate and isofucoxanthinol-dehydrate, degradation products of fucoxanthin and a biomarker for diatoms, were the only carotenols associated with CCEs. The PI also found CCEs in water column samples in regions dominated by diatoms and CCEs were found in the fecal pellets of a copepod fed diatoms in the laboratory. It is suggested that CCEs are produced by enzymatically mediated transesterifications in copepods grazing on diatoms. Thus, sedimentary CCEs could be markers for new production derived from diatoms and the organic carbon and nitrogen isotopic signature would reflect that of the diatoms that contributed to the flux of carbon to the sediments. A set of laboratory experiments will further corroborate this hypothesis. Initially experiments will be performed with the copepod, Calanus pacificus, that is present year-round off California. Matched water column and sediment trap samples from the Santa Barbara Basin and Monterey Bay, covering all seasons, will be used to relate the production of CCEs to phytoplankton community structure and other environmental factors.