Coupled nitrification-denitrification in sediment of the eastern Bering Sea shelf leads to 15N enrichment of fixed N in shelf waters
Article first published online: 5 NOV 2011
Copyright 2011 by the American Geophysical Union.
Journal of Geophysical Research: Oceans (1978–2012)
Volume 116, Issue C11, November 2011
How to Cite
2011), Coupled nitrification-denitrification in sediment of the eastern Bering Sea shelf leads to 15N enrichment of fixed N in shelf waters, J. Geophys. Res., 116, C11006, doi:10.1029/2010JC006751., , , , , , , and (
- Issue published online: 5 NOV 2011
- Article first published online: 5 NOV 2011
- Manuscript Accepted: 12 AUG 2011
- Manuscript Revised: 10 AUG 2011
- Manuscript Received: 22 OCT 2010
- Bering Sea shelf;
- sea ice;
- stable isotopes
 We studied the nitrogen biogeochemistry of the ice-covered eastern Bering Sea shelf using the isotope ratios (15N/14N and 18O/16O) of NO3− and other N species. The 15N/14N of late winter NO3− on the shelf decreases inshore and is inversely correlated with bottom water [NH4+], consistent with an input of low-15N/14N NO3− from partial nitrification of NH4+ remineralized from the sediments. An inshore 15N/14N increase in total dissolved N (TDN) suggests that (1) the sediment-derived NH4+ is elevated in 15N due to the same partial nitrification that yields the low-15N/14N NO3−, and (2) 15N-deplete NO3− from partial nitrification within the sediments is denitrified to N2. The proportion of newly nitrified NO3− on the shelf, evidenced by an inshore decrease in NO3− 18O/16O, is correlated with the N deficit, further implicating nitrification coupled to denitrification; however, a simple N isotope budget indicates a comparable rate of denitrification supported by diffusion of NO3− into the sediments. The isotopic impact of benthic N loss is further demonstrated by a correlation between the 15N/14N of shelf surface sediment and the N deficit of the overlying water column, both of which increase inshore and northward, as well as by Arctic NO3− isotope data indicating that the fixed N transported through Bering Strait has a 15N/14N higher than is found in the open Bering Sea. The significant net isotope effect of benthic N loss on the Bering shelf, 6–8 ‰, is at odds with previous assumptions regarding the global ocean's N isotope budget.