CHLORIN ACCUMULATION RATE AS A PROXY FOR QUATERNARY MARINE PRIMARY PRODUCTIVITY

A KNOWLEDGE Of past changes in the biological productivity of the ocea ns is important for understanding the interactions between carbon cycl ing and climate. Phytoplankton productivity in today's oceans can be e stimated from the concentrations of chlorophyll in sea water(1), but c hlorophyll is not preserved in the sediments. Existing proxies for pas t algal productivity do not represent total productivity; for example, biogenic opal(2) reflects the contribution of only part of the phytop lankton community, and the organic carbon record can be subject to con tamination from terrestrial inputs(2,3). Although chlorins, the pigmen t-transformation products of chlorophyll, are widespread in Quaternary marine sediments, their potential as proxy measures of past variation s in primary productivity has not been convincingly demonstrated. Here we report a high-resolution molecular stratigraphic record of chlorin concentrations over the past 350,000 years in a sediment core from th e subtropical Atlantic continental margin. Maxima in the chlorin accum ulation rate coincide with significant peaks in the accumulation rates of biogenic opal (at the end of glacial terminations) and organic car bon (between terminations). These results suggest that chlorins, unlik e other proxies, can serve as a measure of total primary productivity variations.