Anoxic and oxic degradation of ¹⁴C‐labeled chloropigments and a ¹⁴C‐labeled diatom in Long Island Sound sediments

Abstract

Anoxic and oxic degradation pathways of sedimentary chloropigments were examined by spiking marine sediment with 14 C‐labeled algal cells and purified chloropigments from the diatom Skeletonema costatum. These experiments suggest that Chl a degrades through multiple pathways. Under oxic conditions, most bulk sedimentary Chl a degraded to various colorless compounds and only a minor fraction degraded to pheophytin a ; added 14 C‐labeled Chl a also degraded quickly, but 30–40% of this Chl a was converted to pheophytin a. Under anoxic conditions, only a small fraction of bulk Chl a degraded, but added 14 C‐labeled Chl a continuously degraded and ~30–40% of it was converted to pheophytin a. Pheophytin a is relatively stable under anoxic conditions but degrades under oxic conditions, thus it is a potential end product of chloropigment degradation in anoxic environments. Degradation pathways are likely dependent on the relative proportion of unassociated Chl a to chlorophyll complexes present in the sediment. Only unassociated Chl a appears to be available for anoxic decomposition. Under oxic conditions, some colorless products were further degraded and solubilized; none of the 14 C label added as purified pigments was lost under anoxic conditions during the 1‐month incubation. About 80% of the acetone‐extractable 14 C in labeled cells was lost in 1 month from sediments under oxic conditions and ~30% under anoxic conditions.