TY - JOUR
T1 - Origin of the deep Bering Sea nitrate deficit
T2 - Constraints from the nitrogen and oxygen isotopic composition of water column nitrate and benthic nitrate fluxes
AU - Lehmann, Moritz F.
AU - Sigman, Daniel Mikhail
AU - McCorkle, Daniel C.
AU - Brunelle, Brigitte G.
AU - Hoffmann, Sharon
AU - Kienast, Markus
AU - Cane, Greg
AU - Clement, Jaclyn
PY - 2005/12
Y1 - 2005/12
N2 - On the basis of the normalization to phosphate, a significant amount of nitrate is missing from the deep Bering Sea (BS). Benthic denitrification has been suggested previously to be the dominant cause for the BS nitrate deficit. We measured water column nitrate 15N/14N and 18O/16O as integrative tracers of microbial denitrification, together with pore water-derived benthic nitrate fluxes in the deep BS basin, in order to gain new constraints on the mechanism of fixed nitrogen loss in the BS. The lack of any nitrate isotope enrichment into the deep part of the BS supports the benthic denitrification hypothesis. On the basis of the nitrate deficit in the water column with respect to the adjacent North Pacific and a radiocarbon-derived ventilation age of ∼50 years, we calculate an average deep BS (>2000 m water depth) sedimentary denitrification rate of ∼230 μmol N m-2 d-1 (or 1.27 Tg N yr-1), more than 3 times higher than high-end estimates of the average global sedimentary denitrification rate for the same depth interval. Pore water-derived estimates of benthic denitrification were variable, and uncertainties in estimates were large. A very high denitrification rate measured from the base of the steep northern slope of the basin suggests that the elevated average sedimentary denitrification rate of the deep Bering calculated from the nitrate deficit is driven by organic matter supply to the base of the continental slope, owing to a combination of high primary productivity in the surface waters along the shelf break and efficient down-slope sediment focusing along the steep continental slopes that characterize the BS.
AB - On the basis of the normalization to phosphate, a significant amount of nitrate is missing from the deep Bering Sea (BS). Benthic denitrification has been suggested previously to be the dominant cause for the BS nitrate deficit. We measured water column nitrate 15N/14N and 18O/16O as integrative tracers of microbial denitrification, together with pore water-derived benthic nitrate fluxes in the deep BS basin, in order to gain new constraints on the mechanism of fixed nitrogen loss in the BS. The lack of any nitrate isotope enrichment into the deep part of the BS supports the benthic denitrification hypothesis. On the basis of the nitrate deficit in the water column with respect to the adjacent North Pacific and a radiocarbon-derived ventilation age of ∼50 years, we calculate an average deep BS (>2000 m water depth) sedimentary denitrification rate of ∼230 μmol N m-2 d-1 (or 1.27 Tg N yr-1), more than 3 times higher than high-end estimates of the average global sedimentary denitrification rate for the same depth interval. Pore water-derived estimates of benthic denitrification were variable, and uncertainties in estimates were large. A very high denitrification rate measured from the base of the steep northern slope of the basin suggests that the elevated average sedimentary denitrification rate of the deep Bering calculated from the nitrate deficit is driven by organic matter supply to the base of the continental slope, owing to a combination of high primary productivity in the surface waters along the shelf break and efficient down-slope sediment focusing along the steep continental slopes that characterize the BS.
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U2 - 10.1029/2005GB002508
DO - 10.1029/2005GB002508
M3 - Article
AN - SCOPUS:33244466724
SN - 0886-6236
VL - 19
JO - Global Biogeochemical Cycles
JF - Global Biogeochemical Cycles
IS - 4
ER -