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Significant mixed layer nitrification in a natural iron-fertilized bloom of the Southern Ocean


Fripiat, F and Elskens, M and Trull, TW and Blain, S and Cavagna, AJ and Fernandez, C and Fonseca-Batista, D and Planchon, F and Raimbault, P and Roukaerts, A and Dehairs, F, Significant mixed layer nitrification in a natural iron-fertilized bloom of the Southern Ocean, Global Biogeochemical Cycles, 29, (11) pp. 1929-1943. ISSN 0886-6236 (2015) [Refereed Article]


Copyright Statement

Copyright 2015 American Geophysical Union

DOI: doi:10.1002/2014GB005051


Nitrification, the microbially mediated oxidation of ammonium into nitrate, is generally expected to be low in the Southern Ocean mixed layer. This paradigm assumes that nitrate is mainly provided through vertical mixing and assimilated during the vegetative season, supporting the concept that nitrate uptake is equivalent to the new primary production (i.e., primary production which is potentially available for export). Here we show that nitrification is significant (~40-80% of the seasonal nitrate uptake) in the naturally iron-fertilized bloom over the southeast Kerguelen Plateau. Hence, a large fraction of the nitrate-based primary production is regenerated, instead of being exported. It appears that nitrate assimilation (light dependent) and nitrification (partly light inhibited) are spatially separated between the upper and lower parts, respectively, of the deep surface mixed layers. These deep mixed layers, extending well below the euphotic layer, allow nitrifiers to compete with phytoplankton for the assimilation of ammonium. The high contributions of nitrification to nitrate uptake are in agreement with both low export efficiency (i.e., the percentage of primary production that is exported) and low seasonal nitrate drawdown despite high nitrate assimilation.

Item Details

Item Type:Refereed Article
Keywords:nitritfication, iron fertilization, Southern Ocean
Research Division:Earth Sciences
Research Group:Oceanography
Research Field:Chemical oceanography
Objective Division:Environmental Management
Objective Group:Management of Antarctic and Southern Ocean environments
Objective Field:Antarctic and Southern Ocean oceanic processes
UTAS Author:Trull, TW (Professor Thomas Trull)
ID Code:106055
Year Published:2015
Web of Science® Times Cited:15
Deposited By:CRC-Antarctic Climate & Ecosystems
Deposited On:2016-01-27
Last Modified:2017-11-01
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