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<oai_dc:dc xmlns:dc="http://purl.org/dc/elements/1.1/" xmlns:oai_dc="http://www.openarchives.org/OAI/2.0/oai_dc/" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.openarchives.org/OAI/2.0/oai_dc/ http://www.openarchives.org/OAI/2.0/oai_dc.xsd">
  <dc:contributor>Carol Kendall</dc:contributor>
  <dc:contributor>J.T. Pennington</dc:contributor>
  <dc:contributor>Francisco P. Chavez</dc:contributor>
  <dc:contributor>Adina Paytan</dc:contributor>
  <dc:creator>Scott D. Wankel</dc:creator>
  <dc:date>2007</dc:date>
  <dc:description>&lt;div class="article-section__content en main"&gt;&lt;p&gt;Coupled measurements of nitrate (NO&lt;sub&gt;3&lt;/sub&gt;&lt;sup&gt;−&lt;/sup&gt;), nitrogen (N), and oxygen (O) isotopic composition (&lt;i&gt;δ&lt;/i&gt;&lt;sup&gt;15&lt;/sup&gt;N&lt;sub&gt;NO3&lt;/sub&gt;&lt;span&gt;&amp;nbsp;&lt;/span&gt;and&lt;span&gt;&amp;nbsp;&lt;/span&gt;&lt;i&gt;δ&lt;/i&gt;&lt;sup&gt;18&lt;/sup&gt;O&lt;sub&gt;NO3&lt;/sub&gt;) 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&lt;sub&gt;3&lt;/sub&gt;&lt;sup&gt;−&lt;/sup&gt;&lt;span&gt;&amp;nbsp;&lt;/span&gt;assimilation and nitrification within the euphotic zone. Specifically, increases in&lt;span&gt;&amp;nbsp;&lt;/span&gt;&lt;i&gt;δ&lt;/i&gt;&lt;sup&gt;18&lt;/sup&gt;O&lt;sub&gt;NO3&lt;/sub&gt;&lt;span&gt;&amp;nbsp;&lt;/span&gt;were consistently greater than those in&lt;span&gt;&amp;nbsp;&lt;/span&gt;&lt;i&gt;δ&lt;/i&gt;&lt;sup&gt;15&lt;/sup&gt;N&lt;sub&gt;NO3&lt;/sub&gt;. A coupled isotope steady state box model was used to estimate the amount of NO&lt;sub&gt;3&lt;/sub&gt;&lt;sup&gt;−&lt;/sup&gt;&lt;span&gt;&amp;nbsp;&lt;/span&gt;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&lt;sub&gt;4&lt;/sub&gt;&lt;sup&gt;+&lt;/sup&gt;) consumption, in which NH&lt;sub&gt;4&lt;/sub&gt;&lt;sup&gt;+&lt;/sup&gt;&lt;span&gt;&amp;nbsp;&lt;/span&gt;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&lt;sub&gt;4&lt;/sub&gt;&lt;sup&gt;+&lt;/sup&gt;&lt;span&gt;&amp;nbsp;&lt;/span&gt;oxidation, NH&lt;sub&gt;4&lt;/sub&gt;&lt;sup&gt;+&lt;/sup&gt;&lt;span&gt;&amp;nbsp;&lt;/span&gt;assimilation, and NO&lt;sub&gt;3&lt;/sub&gt;&lt;sup&gt;−&lt;/sup&gt;&lt;span&gt;&amp;nbsp;&lt;/span&gt;assimilation in marine environments.&lt;/p&gt;&lt;/div&gt;</dc:description>
  <dc:format>application/pdf</dc:format>
  <dc:identifier>10.1029/2006GB002723</dc:identifier>
  <dc:language>en</dc:language>
  <dc:publisher>AGU</dc:publisher>
  <dc:title>Nitrification in the euphotic zone as evidenced by nitrate dual isotopic composition: Observations from Monterey Bay, California</dc:title>
  <dc:type>article</dc:type>
</oai_dc:dc>