Molecular weight distribution of proteinaceous material in Long Island Sound sediments

Abstract

Proteinaceous material usually accounts for much of the total nitrogen and organic carbon in marine sediments. Thus, decomposition of protein is frequently investigated as a measure of labile organic matter turnover. The fraction of protein that escapes remineralization to CO2 undergoes transformations that may reflect pathways of preservation in sedimentary environments. We analyzed the molecular weight distribution of sedimentary proteinaceous material extracted with NaOH and evaluated the results in terms of diagenetic changes experienced by this pool. Total protein concentrations were determined in Long Island Sound sediments as total hydrolyzed amino acids (THAA), the sum of concentrations of individual amino acids measured after acid hydrolysis. Although the total fraction of THAA extracted by NaOH decreases slightly downcore, from 55% to 40%, the molecular size of that THAA increases. Proteinaceous material >100 kD increases in relative importance with depth and age of sediment, reaching 70% of the total THAA pool at 3 m depth, or roughly 1,000 yr of sediment accumulation. The fraction of THAA between 10 and 100 kD decreased from 25% to 5% of the total over this depth. The relative abundance of the peptide‐size fraction (<3 kD) remained essentially unchanged. The processes of bacterial production, selective adsorption, geo‐polymerization, and selective preservation were explored to explain these changes.