Cycling of dissolved and particulate organic matter at station Aloha: Insights from 13C NMR spectroscopy coupled with elemental, isotopic and molecular analyses

Molecular analyses of carbohydrates and amino acids characterized ∼9% of the C in UDOM and ∼28% of the C in UPOM. Although a relatively small proportion of the total C was characterizable with molecular analyses, the depth trends and the ratio of amino acids to carbohydrates in UPOM and UDOM were similar to those determined by 13C NMR. This suggests that the organic matter fraction characterized by molecular analyses is representative of the molecularly uncharacterized fraction of organic matter. It is postulated that the molecularly uncharacterized fraction is encapsulated or shielded by a hydrolysis-resistant matrix or the individual amino acid and sugar units have been altered to form a chemical entity unrecognizable by the molecular analyses.