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Nitrification in the euphotic zone as evidenced by nitrate dual isotopic composition: Observations from Monterey Bay, California

Global Biogeochemical Cycles

By:
, , , , and
DOI: 10.1029/2006GB002723

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Abstract

Coupled measurements of nitrate (NO3-), nitrogen (N), and oxygen (O) isotopic composition (??15NNO3 and ??18ONO3) were made in surface waters of Monterey Bay to investigate multiple N cycling processes occurring within surface waters. Profiles collected throughout the year at three sites exhibit a wide range of values, suggesting simultaneous and variable influence of both phytoplankton NO3- assimilation and nitrification within the euphotic zone. Specifically, increases ??18ONO3 were consistently greater than those in ??15NN03. A coupled isotope steady state box model was used to estimate the amount of NO3- supplied by nitrification in surface waters relative to that supplied from deeper water. The model highlights the importance of the branching reaction during ammonium (NH4+) consumption, in which NH4+ either serves as a substrate for regenerated production or for nitrification. Our observations indicate that a previously unrecognized proportion of nitrate-based productivity, on average 15 to 27%, is supported by nitrification in surface waters and should not be considered new production. This work also highlights the need for a better understanding of isotope effects of NH4+ oxidation, NH4+ assimilation, and NO4+ assimilation in marine environments.

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
Nitrification in the euphotic zone as evidenced by nitrate dual isotopic composition: Observations from Monterey Bay, California
Series title:
Global Biogeochemical Cycles
DOI:
10.1029/2006GB002723
Volume
21
Issue:
2
Year Published:
2007
Language:
English
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
Larger Work Title:
Global Biogeochemical Cycles