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<front>
<journal-meta>
<journal-id journal-id-type="publisher">EGUsphere</journal-id>
<journal-title-group>
<journal-title>EGUsphere</journal-title>
<abbrev-journal-title abbrev-type="publisher">EGUsphere</abbrev-journal-title>
<abbrev-journal-title abbrev-type="nlm-ta">EGUsphere</abbrev-journal-title>
</journal-title-group>
<issn pub-type="epub"></issn>
<publisher><publisher-name>Copernicus Publications</publisher-name>
<publisher-loc>Göttingen, Germany</publisher-loc>
</publisher>
</journal-meta>
<article-meta>
<article-id pub-id-type="doi">10.5194/egusphere-2026-2917</article-id>
<title-group>
<article-title>Seasonal stratification regulates carbon allocation between particulate and dissolved pathways in the Gulf of Aqaba</article-title>
</title-group>
<contrib-group><contrib contrib-type="author" xlink:type="simple"><name name-style="western"><surname>Rahav</surname>
<given-names>Eyal</given-names>
<ext-link>https://orcid.org/0000-0001-5697-6684</ext-link>
</name>
<xref ref-type="aff" rid="aff1">
<sup>1</sup>
</xref>
<xref ref-type="aff" rid="aff2">
<sup>2</sup>
</xref>
<xref ref-type="aff" rid="aff3">
<sup>3</sup>
</xref>
</contrib>
<contrib contrib-type="author" xlink:type="simple"><name name-style="western"><surname>Paytan</surname>
<given-names>Adina</given-names>
<ext-link>https://orcid.org/0000-0001-8360-4712</ext-link>
</name>
<xref ref-type="aff" rid="aff2">
<sup>2</sup>
</xref>
</contrib>
</contrib-group><aff id="aff1">
<label>1</label>
<addr-line>Israel Oceanographic and Limnological Research, Haifa, Israel</addr-line>
</aff>
<aff id="aff2">
<label>2</label>
<addr-line>Institute of Marine Science, University of California, Santa Cruz, CA, USA</addr-line>
</aff>
<aff id="aff3">
<label>3</label>
<addr-line>Department of Earth and Environmental Science, Ben-Gurion University of the Negev, Beer Sheva, Israel</addr-line>
</aff>
<pub-date pub-type="epub">
<day>04</day>
<month>06</month>
<year>2026</year>
</pub-date>
<volume>2026</volume>
<fpage>1</fpage>
<lpage>27</lpage>
<permissions>
<copyright-statement>Copyright: &#x000a9; 2026 Eyal Rahav</copyright-statement>
<copyright-year>2026</copyright-year>
<license license-type="open-access">
<license-p>This work is licensed under the Creative Commons Attribution 4.0 International License. To view a copy of this licence, visit <ext-link ext-link-type="uri"  xlink:href="https://creativecommons.org/licenses/by/4.0/">https://creativecommons.org/licenses/by/4.0/</ext-link></license-p>
</license>
</permissions>
<self-uri xlink:href="https://egusphere.copernicus.org/preprints/2026/egusphere-2026-2917/">This article is available from https://egusphere.copernicus.org/preprints/2026/egusphere-2026-2917/</self-uri>
<self-uri xlink:href="https://egusphere.copernicus.org/preprints/2026/egusphere-2026-2917/egusphere-2026-2917.pdf">The full text article is available as a PDF file from https://egusphere.copernicus.org/preprints/2026/egusphere-2026-2917/egusphere-2026-2917.pdf</self-uri>
<abstract>
<p>Water column stratification exerts fundamental control on microbial carbon cycling in oligotrophic areas of the ocean, yet its impact on the partitioning and fate of newly fixed carbon remains insufficiently resolved. Here, we investigated carbon fluxes in the Northern Red Sea, Gulf of Aqaba from 5 cruises conducted during the stratified period. We measured &lt;sup&gt;14&lt;/sup&gt;C-based measurements of primary production partitioned into particulate (&amp;gt;0.7 &amp;micro;m; PP&lt;sub&gt;POC&lt;/sub&gt;) and dissolved (&amp;lt;0.7 &amp;micro;m; PP&lt;sub&gt;DOC&lt;/sub&gt;) fractions, bacterial production (BP), community and bacterial respiration across the euphotic zone (0&amp;ndash;100 m). As stratification intensifies and nutrient supply from depth diminishes, depth-integrated PP&lt;sub&gt;POC&lt;/sub&gt; declined from 1.26 to 0.35 g C m&lt;sup&gt;-2&lt;/sup&gt; d&lt;sup&gt;-1&lt;/sup&gt; while the relative contribution of dissolved carbon pathways increases. The fraction of newly fixed carbon released as dissolved organic carbon (extracellular release; PER) increased from 2.5 % to &amp;gt;7 % of total PP, indicating that a larger fraction of photosynthetically fixed carbon was released into the dissolved C pool. PP&lt;sub&gt;DOC&lt;/sub&gt; (0.02&amp;ndash;0.03 g C m&lt;sup&gt;-2&lt;/sup&gt; d&lt;sup&gt;-1&lt;/sup&gt;) was positively correlated with BP (0.08&amp;ndash;0.16 g C m&lt;sup&gt;-2&lt;/sup&gt; d&lt;sup&gt;-1&lt;/sup&gt;), suggesting that recently released dissolved substrates contribute to sustaining heterotrophic microbial activity. Despite declining primary production, BR remained substantial (0.23&amp;ndash;0.52 g C m&lt;sup&gt;-2&lt;/sup&gt; d&lt;sup&gt;-1&lt;/sup&gt;), resulting in low to moderate bacterial growth efficiency (13&amp;ndash;35 %) and indicating that most processed carbon was respired rather than incorporated into biomass. These findings indicate that summer stratification enhances the relative importance of dissolved carbon release and microbial recycling, thereby reducing the efficiency of carbon transfer to depth in the Gulf of Aqaba and likely other oligotrophic systems.</p>
</abstract>
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