<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE article PUBLIC "-//NLM//DTD Journal Publishing DTD v3.0 20080202//EN" "https://jats.nlm.nih.gov/nlm-dtd/publishing/3.0/journalpublishing3.dtd">
<article xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink" article-type="research-article" specific-use="SMUR" dtd-version="3.0" xml:lang="en">
<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-2026-5095</article-id>
<title-group>
<article-title>Variability in the natural Uranium Isotopic composition of the Arctic Ocean</article-title>
</title-group>
<contrib-group><contrib contrib-type="author" xlink:type="simple"><name name-style="western"><surname>Janecke</surname>
<given-names>Hannah F.</given-names>
<ext-link>https://orcid.org/0009-0000-9760-2742</ext-link>
</name>
<xref ref-type="aff" rid="aff1">
<sup>1</sup>
</xref>
<xref ref-type="aff" rid="aff2">
<sup>2</sup>
</xref>
</contrib>
<contrib contrib-type="author" xlink:type="simple"><name name-style="western"><surname>Greve</surname>
<given-names>Sahra</given-names>
</name>
<xref ref-type="aff" rid="aff1">
<sup>1</sup>
</xref>
</contrib>
<contrib contrib-type="author" xlink:type="simple"><name name-style="western"><surname>Frank</surname>
<given-names>Norbert</given-names>
<ext-link>https://orcid.org/0000-0002-0416-9546</ext-link>
</name>
<xref ref-type="aff" rid="aff1">
<sup>1</sup>
</xref>
</contrib>
</contrib-group><aff id="aff1">
<label>1</label>
<addr-line>Institut für Umweltphysik, Universität Heidelberg, Im Neuenheimer Feld 229, 69120 Heidelberg, Germany</addr-line>
</aff>
<aff id="aff2">
<label>2</label>
<addr-line>Université Paris Cité, Institut de physique du globe de Paris, CNRS, F-75005 Paris, France</addr-line>
</aff>
<pub-date pub-type="epub">
<day>08</day>
<month>09</month>
<year>2026</year>
</pub-date>
<volume>2026</volume>
<fpage>1</fpage>
<lpage>28</lpage>
<permissions>
<copyright-statement>Copyright: &#x000a9; 2026 Hannah F. Janecke et al.</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-2026-5095/">This article is available from https://egusphere.copernicus.org/preprints/2026/egusphere-2026-5095/</self-uri>
<self-uri xlink:href="https://egusphere.copernicus.org/preprints/2026/egusphere-2026-5095/egusphere-2026-5095.pdf">The full text article is available as a PDF file from https://egusphere.copernicus.org/preprints/2026/egusphere-2026-5095/egusphere-2026-5095.pdf</self-uri>
<abstract>
<p>The Arctic Ocean plays a significant role in the Global Thermohaline Circulation and is strongly sensitive to ongoing changes. Due to climate change, rising riverine freshwater inputs into the Arctic Ocean and rising instability of the Arctic Ice covering have been observed. The resulting changes in the ocean mixing and circulation can give valuable insights on future impacts. Here, we study whether over the past twenty years additional freshwater input is traceable in the isotopic composition of uranium, using the natural uranium &lt;sup&gt;234&lt;/sup&gt;U/&lt;sup&gt;238&lt;/sup&gt;U isotope composition. Water samples taken at six stations across the Arctic Ocean are analyzed using high-precision MC-ICP-MS. For each station, a depth profile of &lt;sup&gt;234&lt;/sup&gt;U/&lt;sup&gt;238&lt;/sup&gt;U ratios, as &amp;permil; deviation from secular equilibrium (&amp;delta;&lt;sup&gt;234&lt;/sup&gt;U), is obtained and compared to a previous study by Andersen et al. (2007), which included similar stations taken 20 years prior. Surface water &amp;delta;&lt;sup&gt;234&lt;/sup&gt;U reveals overall 1&amp;ndash;2 &amp;permil; lower values as compared to 20 years ago, thus increased freshwater contributions, which are rich in &lt;sup&gt;234&lt;/sup&gt;U, are not traced within the upper 30m of the Arctic Ocean. Instead a stronger downward mixing over the past 20 years is detected. Below 300 m &amp;delta;&lt;sup&gt;234&lt;/sup&gt;U is homogeneous within measurement uncertainty and yields a &amp;delta;&lt;sup&gt;234&lt;/sup&gt;U value of 146.94 &amp;permil; &amp;plusmn; 0.09 &amp;permil; (2&amp;sigma; mean, N=88, HU1-equilibrium scale), which is identical to the global ocean mean value of 146.75 &amp;plusmn; 0.28 by Kipp et al. (2022) and confirms that the interior Arctic U isotope composition is in steady state and set by the long-term global ocean circulation. In addition, we determined the Arctic Ocean &lt;sup&gt;238&lt;/sup&gt;U/&lt;sup&gt;235&lt;/sup&gt;U ratio obtaining a mean &amp;delta;&lt;sup&gt;238&lt;/sup&gt;U value of &amp;minus;0.348 &amp;permil; &amp;plusmn; 0.046 &amp;permil; (N=68) that is also identical within uncertainty to the global Ocean mean &amp;delta;&lt;sup&gt;238&lt;/sup&gt;U value of &amp;minus;0.379 &amp;permil; &amp;plusmn; 0.023 &amp;permil; (Kipp et al., 2022) indicating absence of local redox conditions on the Arctic Ocean U cycle.</p>
</abstract>
<counts><page-count count="28"/></counts>
</article-meta>
</front>
<body/>
<back>
</back>
</article>