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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>Felisa Wolfe-Simon</dc:contributor>
  <dc:contributor>Rebecca S. Robinson</dc:contributor>
  <dc:contributor>Yelun Qin</dc:contributor>
  <dc:contributor>Mark A. Saito</dc:contributor>
  <dc:contributor>Ann Pearson</dc:contributor>
  <dc:creator>Meytal B. Higgins</dc:creator>
  <dc:date>2011</dc:date>
  <dc:description>&lt;p&gt;&lt;span&gt;Natural variations in the ratios of nitrogen isotopes in biomass reflect variations in nutrient sources utilized for growth. In order to use &amp;delta;&lt;/span&gt;&lt;sup&gt;15&lt;/sup&gt;&lt;span&gt;N values of chloropigments of photosynthetic organisms to determine the corresponding &amp;delta;&lt;/span&gt;&lt;sup&gt;15&lt;/sup&gt;&lt;span&gt;N values of biomass &amp;ndash; and by extension, surface waters &amp;ndash; the isotopic offset between chlorophyll and biomass must be constrained. Here we examine this offset in various geologically-relevant taxa, grown using nutrient sources that may approximate ocean conditions at different times in Earth&amp;rsquo;s history. Phytoplankton in this study include cyanobacteria (diazotrophic and non-diazotrophic), eukaryotic algae (red and green), and anoxygenic photosynthetic bacteria (Proteobacteria), as well as environmental samples from sulfidic lake water. Cultures were grown using N&lt;/span&gt;&lt;sub&gt;2&lt;/sub&gt;&lt;span&gt;, NO&lt;/span&gt;&lt;sub&gt;3&lt;/sub&gt;&lt;sup&gt;&amp;minus;&lt;/sup&gt;&lt;span&gt;, and NH&lt;/span&gt;&lt;sub&gt;4&lt;/sub&gt;&lt;sup&gt;+&lt;/sup&gt;&lt;span&gt;&amp;nbsp;as nitrogen sources, and were examined under different light regimes and growth conditions. We find surprisingly high variability in the isotopic difference (&amp;delta;&lt;/span&gt;&lt;sup&gt;15&lt;/sup&gt;&lt;span&gt;N&lt;/span&gt;&lt;sub&gt;biomass&lt;/sub&gt;&lt;span&gt;&amp;nbsp;&amp;minus;&amp;nbsp;&amp;delta;&lt;/span&gt;&lt;sup&gt;15&lt;/sup&gt;&lt;span&gt;N&lt;/span&gt;&lt;sub&gt;chloropigment&lt;/sub&gt;&lt;span&gt;) for prokaryotes, with average values for species ranging from &amp;minus;12.2&amp;permil; to +11.7&amp;permil;. We define this difference as&amp;nbsp;&lt;/span&gt;&lt;i&gt;&amp;epsilon;&lt;/i&gt;&lt;sub&gt;por&lt;/sub&gt;&lt;span&gt;, a term that encompasses diagenetic porphyrins and chlorins, as well as chlorophyll. Negative values of&amp;nbsp;&lt;/span&gt;&lt;i&gt;&amp;epsilon;&lt;/i&gt;&lt;sub&gt;por&lt;/sub&gt;&lt;span&gt;&amp;nbsp;reflect chloropigments that are&amp;nbsp;&lt;/span&gt;&lt;sup&gt;15&lt;/sup&gt;&lt;span&gt;N-enriched relative to biomass. Notably, this enrichment appears to occur only in cyanobacteria. The average value of&amp;nbsp;&lt;/span&gt;&lt;i&gt;&amp;epsilon;&lt;/i&gt;&lt;sub&gt;por&lt;/sub&gt;&lt;span&gt;&amp;nbsp;for freshwater cyanobacterial species is &amp;minus;9.8&amp;nbsp;&amp;plusmn;&amp;nbsp;1.8&amp;permil;, while for marine cyanobacteria it is &amp;minus;0.9&amp;nbsp;&amp;plusmn;&amp;nbsp;1.3&amp;permil;. These isotopic effects group environmentally but not phylogenetically, e.g.,&amp;nbsp;&lt;/span&gt;&lt;i&gt;&amp;epsilon;&lt;/i&gt;&lt;sub&gt;por&lt;/sub&gt;&lt;span&gt;&amp;nbsp;values for freshwater Chroococcales resemble those of freshwater Nostocales but differ from those of marine Chroococcales. Our measured values of&amp;nbsp;&lt;/span&gt;&lt;i&gt;&amp;epsilon;&lt;/i&gt;&lt;sub&gt;por&lt;/sub&gt;&lt;span&gt;&amp;nbsp;for eukaryotic algae (range&amp;nbsp;=&amp;nbsp;4.7&amp;ndash;8.7&amp;permil;) are similar to previous reports for pure cultures. For all taxa studied, values of&amp;nbsp;&lt;/span&gt;&lt;i&gt;&amp;epsilon;&lt;/i&gt;&lt;sub&gt;por&lt;/sub&gt;&lt;span&gt;&amp;nbsp;do not depend on the type of nitrogen substrate used for growth. The observed environmental control of&amp;nbsp;&lt;/span&gt;&lt;i&gt;&amp;epsilon;&lt;/i&gt;&lt;sub&gt;por&lt;/sub&gt;&lt;span&gt;&amp;nbsp;suggests that values of&amp;nbsp;&lt;/span&gt;&lt;i&gt;&amp;epsilon;&lt;/i&gt;&lt;sub&gt;por&lt;/sub&gt;&lt;span&gt;&amp;nbsp;could be useful for determining the fractional burial of eukaryotic vs. cyanobacterial organic matter in the sedimentary record.&lt;/span&gt;&lt;/p&gt;</dc:description>
  <dc:format>application/pdf</dc:format>
  <dc:identifier>10.1016/j.gca.2011.04.024</dc:identifier>
  <dc:language>en</dc:language>
  <dc:publisher>Elsevier</dc:publisher>
  <dc:title>Paleoenvironmental implications of taxonomic variation among δ&lt;sup&gt;15&lt;/sup&gt;N values of chloropigments</dc:title>
  <dc:type>article</dc:type>
</oai_dc:dc>