Abiotic Racemization Kinetics of Amino Acids in Marine Sediments

Abstract

The ratios of D- versus L-amino acids can be used to infer the sources and composition of sedimentary organic matter. Such inferences, however, rely on knowing the rates at which amino acids in sedimentary organic matter racemize abiotically between the D- and the L-forms. Based on a heating experiment, we report kinetic parameters for racemization of aspartic acid, glutamic acid, serine, and alanine in bulk sediment from Aarhus Bay, Denmark, taken from the surface, cm, and cm depth below seafloor. Extrapolation to a typical cold deep sea sediment temperature of uC suggests racemization rate constants of 0.50 25–1161025 yr21. These results can be used in conjunction with measurements of sediment age to predict the ratio of D:L amino acids due solely to abiotic racemization of the source material, deviations from which can indicate the abundance and turnover of active microbial populations.