Proteinaceous material usually accounts for much of the total nitrogen and
organic carbon in marine sediments. Thus, decomposition of protein is frequ
ently investigated as a measure of labile organic matter turnover. The frac
tion of protein that escapes remineralization to CO2 undergoes transformati
ons 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 diagenet
ic changes experienced by this pool. Total protein concentrations were dete
rmined 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 increa
ses. Proteinaceous material >100 kD increases in relative importance with d
epth 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 r
elative abundance of the peptide-size fraction (<3 kD) remained essentially
unchanged. The processes of bacterial production, selective adsorption, ge
o-polymerization, and selective preservation were explored to explain these
changes.