Chromatographic and SCDP measurements of fossil phorbins and the postglacial history of Little Round Lake, Ontario

Abstract

Estimates are compared of total chlorophyll derivatives from the sediments of meromictic Little Round Lake, Ontario, as determined by the relative SCDP procedure and by quantitative paper chromatographic fractionation. Contrasting profiles of total phorbins were obtained with the two techniques. By comparing SCDP:chromatographic phorbin ratios with extinction coefficients of purified derivatives, the discrepancies are tentatively ascribed to errors in the SCDP procedure resulting from variations in a phorbin composition, interference by b phorbins, and possible interference by nonphorbin contaminants in the 90% acetone extracts. SCDP data must, therefore, be interpreted with great care. From the algal phorbin data and additional information on bacterial phorbins, bacterial carotenoids, and the contemporary limnology of Little Round Lake, it appears that primary productivity increased to a maximum early in postglacial time and then declined progressively to the present low levels. The decline began with the probable onset of biogenic meromixis shortly after the early production maximum. The a : b phorbin ratio indicates strong differential diagenesis of the a phorbins in the lake and also the dominance of plankton containing only chlorophyll a (probably cyanophytes) since the beginning of agriculture in the area.