Pigment preservation and remineralization in oxic coastal marine sediments

Abstract

Complex mixtures of sedimentary chlorophyll degradation products were measured using high performance liquid chromatography (HPLC) in 210Pb dated box- and piston-core sediments. Sediments were collected from Dabob Bay, Washington, a coastal marine fjord conducive to studies yielding an understanding of the remineralization and diagenesis of organic carbon. Greater than 99% of the pheopigment flux out of the water column does not accumulate in the top 2 cm of sediment. Surface sediment pigment profiles indicate that pheophorbides are the dominant pheopigments observed, with concentrations decreasing rapidly with depth. Concentrations of chlorophyll c derivatives also decrease rapidly, but ratios of a/c pheopigments remain within ranges reported for natural and cultured phytoplankton. Sharp pheopigment concentration decreases within the bioturbated surface sediments (as defined by 210Pb activities) were modeled using a one dimensional mixing model. The in situ pheopigment decomposition rate, corrected for bioturbation and sediment accumulation, corresponds to an approximate half-life of 40 days. Sedimentary humic acid, fulvic acid, and residual humin associated pheopigments in sediments which had been previously acetone extracted to remove the lipophilic pheopigment fraction were typed by chromic acid oxidation and release of pyrrole derived maleimides. This humic associated pyrrole derived nitrogen, while a small fraction of total sedimentary or humic nitrogen, accounted for 16–75% of the total sedimentary pheopigment accumulation, and may be significant in understanding the diagenetic fate and transformation of pheopigments to petroporphyrins.