Effects of zooplankton herbivory on biomarker proxy records

The stable carbon isotopic compositions of cholesterol, generally the most dominant sterol in the copepod Temora, bears the delta(13)C "signature" of its dietary precursor sterol when fed on Isochrysis galbana and Rhodomonas sp. The delta(13)C of cholesterol in the faecal pellets released from Temor a longicornis fed on Rhodomonas sp. is identical to the delta(13)C Of the s terols in the diet, indicating that no significant carbon isotopic fraction ation effects occur when the copepod modifies eukaryotic precursor sterols to cholesterol. Furthermore, the ratio of long-chain alkenones and their st able carbon isotopic compositions in I. galbana were identical to those ege sted in faecal material. Thus zooplankton herbivory does not invalidate the use of these alkenones as a proxy for sea surface temperature and pCO(2).