Premium
Detection of Transient Denitrification During a High Organic Matter Event in the Black Sea
Author(s) -
Fuchsman Clara A.,
Paul Barbara,
Staley James T.,
Yakushev Evgeniy V.,
Murray James W.
Publication year - 2019
Publication title -
global biogeochemical cycles
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.512
H-Index - 187
eISSN - 1944-9224
pISSN - 0886-6236
DOI - 10.1029/2018gb006032
Subject(s) - anoxic waters , denitrification , organic matter , environmental chemistry , water column , nitrate , particulates , chemistry , ammonium , environmental science , oceanography , geology , nitrogen , organic chemistry
N 2 production by denitrification can occur in anoxic water or potentially inside organic particles. Here we compare data from the Black Sea, a permanently anoxic basin, during two organic matter regimes: suspended particulate organic matter concentrations were high in the oxycline after the spring bloom in March 2005 compared to lower organic matter concentrations in June 2005, May and October 2007, July 2008, and May 2001. For all cruises, N 2 gas had a maximum in the suboxic zone (O 2 < 10 μmol/L). During the high organic matter event (March 2005), an additional shallower N 2 gas and δ 15 N‐N 2 maxima occurred above the suboxic zone in the oxycline where oxygen concentrations were 30–50 μmol/L. Examination of 16S rRNA indicated that anammox bacteria were not present in the oxycline. The δ 15 N of biologically produced N 2 in the oxycline in March 2005 was significantly enriched (+7‰ to +38‰), not depleted, as would be expected from water column fractionation. A simple diffusion calculation indicated that ammonium produced from remineralization inside particles could be oxidized to nitrate and then completely consumed by denitrification inside the particle. In this calculation, half of denitrified N atoms originated from organic N [ δ 15 N = 11‰] and half of N atoms originated from ambient nitrate [ δ 15 N = 5‰–7‰], producing enriched δ 15 N‐N 2 values. We suggest that denitrifiers were active in microzones inside particulates in hypoxic waters above the suboxic zone of the Black Sea. Denitrification in particles may also explain previous data from the oxycline above ocean oxygen deficient zones.