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Nitrogen cycling in the secondary nitrite maximum of the eastern tropical North Pacific off Costa Rica
Author(s) -
Buchwald Carolyn,
Santoro Alyson E.,
Stanley Rachel H. R.,
Casciotti Karen L.
Publication year - 2015
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 - 10.1002/2015gb005187
Subject(s) - nitrite , nitrate , anammox , environmental chemistry , chemistry , nitrite reductase , denitrification , nitrogen , nitrogen cycle , denitrifying bacteria , organic chemistry
Abstract Nitrite is a central intermediate in the marine nitrogen cycle and represents a critical juncture where nitrogen can be reduced to the less bioavailable N 2 gas or oxidized to nitrate and retained in a more bioavailable form. We present an analysis of rates of microbial nitrogen transformations in the oxygen deficient zone (ODZ) within the eastern tropical North Pacific Ocean (ETNP). We determined rates using a novel one‐dimensional model using the distribution of nitrite and nitrate concentrations, along with their natural abundance nitrogen (N) and oxygen (O) isotope profiles. We predict rate profiles for nitrate reduction, nitrite reduction, and nitrite oxidation throughout the ODZ, as well as the contributions of anammox to nitrite reduction and nitrite oxidation. Nitrate reduction occurs at a maximum rate of 25 nM d −1 at the top of the ODZ, at the same depth as the maximum rate of nitrite reduction, 15 nM d −1 . Nitrite oxidation occurs at maximum rates of 10 nM d −1 above the secondary nitrite maximum, but also in the secondary nitrite maximum, within the ODZ. Anammox contributes to nitrite oxidation within the ODZ but cannot account for all of it. Nitrite oxidation within the ODZ that is not through anammox is also supported by microbial gene abundance profiles. Our results suggest the presence of nitrite oxidation within the ETNP ODZ, with implications for the distribution and physiology of marine nitrite‐oxidizing bacteria, and for total nitrogen loss in the largest marine ODZ.