A synopsis of data on the amino acid compositions of Arctic and Antarctic seawater, XAD-fractions of dissolved organic matter (DOM) and suspended particulate organic material (POM) is presented. Total dissolved amino acids (TDAA) correlated highly significantly with dissolved organic nitrogen (DON), representing about 11% of DON in unfractionated filtered seawater. Average DON values were similar with ca. 3–4 μM N in the Arctic and Antarctic. Differences in amino acid distribution and composition patterns in particulate and dissolved material suggest the selective preservation or utilization of certain amino acids. In POM, glycine, alanine, glutamic acid, aspartic acid and serine made up ca. 50% of the total, while the same amino acids represented 70–80% of TDAA in unfractionated seawater and in the “humic” XAD-fractions. The mole percentage of glycine increases from POM (8%) to bulk filtered seawater (27%), reaching 33–45% in the hydrophobic neutral (HbN), alcohol-soluble fraction of DOM. Evidence is presented for a selective utilization of aspartic acid and its enrichment in the non-humified fraction of DOM. In both regions, at the surface ca. 60%, and at depths > 500 m almost 100% of TDAA is found in the “humic” fractions. A background value of TDAA of around 200 nM, mostly contained in the HbN fraction, is present throughout the water column, probably forming part of recalcitrant molecules. The relation of these findings to different humification mechanisms is discussed.
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