Crenarchaea and phytoplankton coupling in sedimentary archives: Common trigger or metabolic dependence?

The concentrations of chlorins (chlorophyll transformation products indicative of phytoplankton production) and crenarchaeol (a marker for Crenarchaea abundance) are significantly positively correlated (Spearman's rank correlation coefficient r(s) > 0.75) in four core records from freshwater (Lake Baikal) and marine settings (Southern, Atlantic, and Arctic Oceans). This suggests a close relationship between Crenarchaea abundance and phytoplankton production. Degradation and transport mechanisms, as well as a common environmental trigger, may in part account for our observations, but these mechanisms alone cannot fully explain them. Instead our findings point to a metabolic dependence of Crenarchaea on resources released by phytoplankton, such as organic carbon or ammonium.