Composition and stratigraphy of the fossil phorbin derivatives of Little Round Lake, Ontario

Abstract

The chlorophyll derivatives from the sediment of meromictic Little Round Lake, Ontario, have been analyzed by artifact‐free paper chromatography. Sixteen native and allomerized a and b chlorophylls, chlorophyllides, pheophytins, and pheophorbides, together with bacteriopheophytin a and one unknown phorbin, were isolated from the core. No chlorophyll c derivatives were found. An average of 52% of the phorbins were devoid of Mg, 19% were allomerized, and 47% had lost the phytol group. Unaltered native chlorophyll b occurred in much higher proportions (22%) than chlorophyll a (0.3%), indicating that the b phorbins are more resistant than the a pigments to diagenesis. Continuous changes in derivative proportions with depth were not apparent; hence, little phorbin diagenesis occurred after burial in the sediment. The complexity of the profiles from this one lake suggests that using chlorophyll derivatives as paleolimnological indicators will be difficult.