Amino acids and hexosamines as indicators of organic matter degradation state inNorth Sea sediments

Sediment cores from six stations in the eastern North Sea were analyzed for protein amino acids, the nonprotein amino acids β‐alanine and γ‐ aminobutyric acid and the hexosamines galactosamine and glucosamine, and bulk parameters (organic carbon, nitrogen, total hydrolyzable amino acids and carbohydrates) in order to establish the degradation state of sedimentary organic matter. The study sites were selected on the basis of their different physical settings and macrofaunal communities so that a broad quality range in the organic matter would likely be covered. To test if the molecular parameters provide a robust matrix for quality determination, we integrated our results with complementary literature data ranging from marine source organisms to deep‐sea environments. A principal component analysis based on the mole percent contribution of amino acids show4 that there are systematic variations in the amino acid spectra as a consequence of degradation of organic matter. Comparison with more established quality parameters such as hexosamines confirmed that amino acids reflect the degradation state of the organic matter. The amino acids glycine, serine, and threonine were enriched in the more degraded material, and others, such as phenylalanine, glutamic acid, tyrosine, leucine, and isoleucinc, became depleted with increasing degradation state. Selective preservation of structural compounds (diatom cell walls, chitinous organic matter) vs. preferential breakdown of cell plasma material appears to be the reason for the contrastin,; behavior of these molecular compounds. Some of the essential amino acids for macrofauna nutrition (arginine, methionine, and histidine) occurred in lower concentrations in the North Sea sediments compared to organism tissue and therefore may be limiting to growth of deposit‐feeders.