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Dissolved Organic Nitrogen Production and Consumption in Eastern Tropical South Pacific Surface Waters
Author(s) -
Knapp A. N.,
Casciotti K. L.,
Prokopenko M. G.
Publication year - 2018
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 - 10.1029/2017gb005875
Subject(s) - photic zone , upwelling , new production , oceanography , nitrate , nitrogen , isotopes of nitrogen , environmental science , chlorophyll a , surface water , phytoplankton , δ15n , stable isotope ratio , environmental chemistry , nutrient , δ13c , geology , chemistry , ecology , biology , botany , organic chemistry , physics , quantum mechanics , environmental engineering
Models of dissolved organic nitrogen (DON) production and consumption indicate that marine DON is produced in the euphotic zone, especially in upwelling environments, and is consumed as it transits into more oligotrophic regions where it may support export production. However, evaluation of such models is data limited, and in particular, few measurements of DON concentration and/or nitrogen isotopic composition (“δ 15 N”) exist from the South Pacific. Here we present measurements of the concentration and δ 15 N of DON collected in the eastern tropical South Pacific during the austral summers of 2010 (El Niño) and 2011 (La Niña). The concentration and δ 15 N of DON from the eastern tropical South Pacific are broadly consistent with prior measurements elsewhere, that is, DON concentrations of 5 ± 1 μM and DON δ 15 N of 5 ± 1‰, but variations were associated with DON production and consumption. Specifically, surface ocean chlorophyll a concentrations were highly correlated with upper 50‐m DON stocks ( r = 0.96), consistent with a photosynthetic source for DON. Additionally, upper 50‐m DON stocks and their δ 15 N were significantly negatively correlated ( r = −0.84, p = 0.0006), indicating that DON was consumed in surface waters with an isotope effect of 5.5 ± 1.2‰. These results inform our understanding of the controls of DON distributions in the surface ocean and indicate that DON may support export production in nitrate‐poor surface waters, which may decouple new from gross production.