Mathematics – Logic
Scientific paper
Nov 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011gecoa..75.7180p&link_type=abstract
Geochimica et Cosmochimica Acta, Volume 75, Issue 22, p. 7180-7199.
Mathematics
Logic
Scientific paper
Biologically available nitrogen (fixed N) is removed from the oceans by metabolic conversion of inorganic N forms (nitrate and ammonium) to N 2 gas. Much of this removal occurs in marine sediments, where reaction rates are thought to be limited by diffusion. We measured the concentration and isotopic composition of major dissolved nitrogen species in anoxic sediments off the coast of California. At depths below the diffusive penetration of nitrate, we found evidence of a large nitrate pool transported into the sediments by motile microorganisms. A ˜20‰ enrichment in 15 N and 18 O of this biologically transported nitrate over bottom water values and elevated [N 2 ] and δ 15 N-N 2 at depth indicate that this nitrate is consumed by enzymatic redox reactions with the production of N 2 as the end product. Elevated N 2 O concentrations in pore waters below the nitrate diffusion depth confirm that these reactions include the denitrification pathway. A data-constrained model shows that at least 31% of the total N 2 production in anoxic sediments is linked to nitrate bio-transport. Under suboxic/anoxic regimes, this nitrate bio-transport augments diffusive transport, thus increasing benthic fixed nitrogen losses and the reducing burial efficiency of sedimentary organic matter.
Barnett Bruce
Berelson William M.
Chong Lance
Hammond Douglas E.
Prokopenko Maria G.
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