Biogeochemical cycling in an organic-rich coastal marine basin: 11. The sedimentary cycling of dissolved, free amino acids

Details Biogeochemical cycling in an organic-rich coastal marine basin: 11. The sedimentary cycling of dissolved, free amino acids Biogeochemical cycling in an organic-rich coastal marine basin: 11. The sedimentary cycling of dissolved, free amino acids

Nov 1990

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1990gecoa..54.3033b&link_type=abstract

Geochimica et Cosmochimica Acta, vol. 54, Issue 11, pp.3033-3052

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Scientific paper

In the anoxic sediments of Cape Lookout Bight, NC, concentrations of total dissolved free amino acids (TDFAAs) are highest near the sediment-water interface (generally 20 to 60 M), and decrease to non-zero, asymptotic concentrations (2 to 5 M) at depths greater than 20 cm. TDFAAs in the overlying waters are <1 M. Dissolved free amino acid (DFAA) profiles often show a secondary sub-surface maximum in the region between the 1 and 5 mM sulfate isopleths. This phenomenon appears to be related to the transition in the sediments of this region from sulfate reduction to methanogenesis. Aspartic acid, glutamic acid, -aminoglutaric acid, glycine and alanine are the major DFAAs. With depth, -aminoglutaric acid becomes the dominant DFAA, accounting for up to 50 mol%. The mole percentages of individual amino acids in the DFAA and sedimentary (I.E., acid hydrolyzable) pools show some similarities, although microbial and abiotic processes cause several differences to exist. A steady-state diagenetic model which quantifies the processes affecting DFAAs in these sediments yields rates of DFAA production and consumption that agree reasonably well with independent estimates of these quantities in Cape Lookout Bight and other anoxic marine sediments. The combined results of modelling pore water DFAA and sedimentary amino acid profiles indicate that significant exchange of amino acids occurs between the sediments and pore waters (I.E., there is a much larger gross flux through, or turnover of, the DFAA pool than there is a net change in the concentration of sedimentary amino acids). DFAAs produced as intermediates in the remineralization of sedimentary amino acids are both metabolized to inorganic nutrients as well as re-incorporated back into the sediments. This latter process appears most likely to occur by incorporation of DFAAs into sedimentary bacterial biomass, although abiotic processes (E.G., geopolymerization ) may also be of some importance. These results demonstrate that the biogeochemistry of dissolved free amino acids in the pore waters of Cape Lookout Bight sediments is dominated by `internal' transformations (I.E., production from sedimentary amino acids, microbial remineralization, and reincorporation back into the sediments). There is some uncertainty in the magnitude of the flux of DFAAs across the sediment-water interface, although it appears to be of secondary importance when compared to the other sedimentary processes affecting DFAAs.

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