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

Scott D. Wankel; Carol Kendall; J.T. Pennington; Francisco P. Chavez; Adina Paytan

doi:10.1029/2006gb002723

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

Scott D. Wankel·Carol Kendall·J.T. Pennington·Francisco P. Chavez·Adina Paytan

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Abstract

Coupled measurements of nitrate (NO 3 − ), nitrogen (N), and oxygen (O) isotopic composition ( δ 15 N NO3 and δ 18 O NO3 ) 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 NO 3 − assimilation and nitrification within the euphotic zone. Specifically, increases in δ 18 O NO3 were consistently greater than those in δ 15 N NO3 . A coupled isotope steady state box model was used to estimate the amount of NO 3 − supplied by nitrification in surface waters relative to that supplied from deeper water. The model highlights the importance of the branching reaction during ammonium (NH 4 + ) consumption, in which NH 4 + 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 NH 4 + oxidation, NH 4 + assimilation, and NO 3 − assimilation in marine environments.

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Source-reported bounding extent: 36.48976535146369° to 36.98939086733937° latitude; -122.21466064453125° to -121.77246093750001° longitude. This indicates report coverage, not an exact sampling location. View area on OpenStreetMap.

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Scott D. Wankel, Carol Kendall, J.T. Pennington, Francisco P. Chavez, Adina Paytan. 2007-05-04. Nitrification in the euphotic zone as evidenced by nitrate dual isotopic composition: Observations from Monterey Bay, California. https://doi.org/10.1029/2006gb002723

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