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

Wankel, S. D.; Kendall, C.; Pennington, J. T.; Chavez, F. P.; Paytan, A.

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.

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Article

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70029699

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Wankel, S. D.; Kendall, C.; Pennington, J. T.; Chavez, F. P.; Paytan, A.

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English

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Global Biogeochemical Cycles

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Nitrification in the euphotic zone as evidenced by nitrate dual isotopic composition: Observations from Monterey Bay, California; 2007; Article; Journal; Global Biogeochemical Cycles; Wankel, S. D.; Kendall, C.; Pennington, J. T.; Chavez, F. P.; Paytan, A.