Julie N. Richey
Amanda Gerotto
Amelia Shevenell
Marcia C. Bicego
Felipe A. Toledo
Michel M. de Mahiques
Renata H. Nagai
Felipe Stanchak
2025
<p><span>The paleothermometer based on the alkenone unsaturation index (</span><span class="math"><span id="MathJax-Element-6-Frame" class="MathJax_SVG" data-mathml="<math xmlns="http://www.w3.org/1998/Math/MathML"><msubsup is="true"><mtext is="true">U</mtext><mrow is="true"><mtext is="true">37</mtext></mrow><msup is="true"><mrow is="true"><mtext is="true">K</mtext></mrow><mo is="true">&#x2032;</mo></msup></msubsup></math>"><span class="MJX_Assistive_MathML">U37K′</span></span></span><span>) is often used to reconstruct past sea surface temperatures (SST). In the SW Atlantic Ocean, however, a limited understanding of the seasonal and depth distribution of coccolithophores, which generates the </span><span class="math"><span id="MathJax-Element-7-Frame" class="MathJax_SVG" data-mathml="<math xmlns="http://www.w3.org/1998/Math/MathML"><msubsup is="true"><mtext is="true">U</mtext><mrow is="true"><mtext is="true">37</mtext></mrow><msup is="true"><mrow is="true"><mtext is="true">K</mtext></mrow><mo is="true">&#x2032;</mo></msup></msubsup></math>"><span class="MJX_Assistive_MathML">U37K′</span></span></span><span> signal preserved in ocean sediments, hinders accurate estimates of past regional SSTs. We analyzed 45 core-top sediment samples from the continental shelf of the South Brazilian Bight (SBB, 23 °S to 28 °S) to assess regional spatial </span><span class="math"><span id="MathJax-Element-8-Frame" class="MathJax_SVG" data-mathml="<math xmlns="http://www.w3.org/1998/Math/MathML"><msubsup is="true"><mtext is="true">U</mtext><mrow is="true"><mtext is="true">37</mtext></mrow><msup is="true"><mrow is="true"><mtext is="true">K</mtext></mrow><mo is="true">&#x2032;</mo></msup></msubsup></math>"><span class="MJX_Assistive_MathML">U37K′</span></span></span><span>-SST gradients and improve SST estimates. The </span><span class="math"><span id="MathJax-Element-9-Frame" class="MathJax_SVG" data-mathml="<math xmlns="http://www.w3.org/1998/Math/MathML"><msubsup is="true"><mtext is="true">U</mtext><mrow is="true"><mtext is="true">37</mtext></mrow><msup is="true"><mrow is="true"><mtext is="true">K</mtext></mrow><mo is="true">&#x2032;</mo></msup></msubsup></math>"><span class="MJX_Assistive_MathML">U37K′</span></span></span><span> data were converted to SST using six published paleotemperature equations and compared to modern observational SST data from the World Ocean Atlas (2018) data set. Data indicate that the </span><span class="math"><span id="MathJax-Element-10-Frame" class="MathJax_SVG" data-mathml="<math xmlns="http://www.w3.org/1998/Math/MathML"><msubsup is="true"><mtext is="true">U</mtext><mrow is="true"><mtext is="true">37</mtext></mrow><msup is="true"><mrow is="true"><mtext is="true">K</mtext></mrow><mo is="true">&#x2032;</mo></msup></msubsup></math>"><span class="MJX_Assistive_MathML">U37K′</span></span></span><span> signal is produced during the austral summer and autumn when regional episodic upwelling events occur over the inner-shelf and the nutricline shoals at the slope. Our analysis of core-top data shows that SST estimates derived from most calibration equations closely align with modern observed temperatures but are skewed toward warmer months associated with upwelling-derived nutrients. Our findings underscore the importance of considering regional and seasonal biases to improve the accuracy of paleotemperature reconstructions. Understanding the factors influencing the SBB </span><span class="math"><span id="MathJax-Element-11-Frame" class="MathJax_SVG" data-mathml="<math xmlns="http://www.w3.org/1998/Math/MathML"><msubsup is="true"><mtext is="true">U</mtext><mrow is="true"><mtext is="true">37</mtext></mrow><msup is="true"><mrow is="true"><mtext is="true">K</mtext></mrow><mo is="true">&#x2032;</mo></msup></msubsup></math>"><span class="MJX_Assistive_MathML">U37K′</span></span></span><span> signal enables a more meaningful comparison between regional paleoceanographic studies, improving our understanding of past changes in the SW Atlantic Ocean and our ability to predict regional SST response to ongoing and future warming.</span></p>
application/pdf
10.1016/j.orggeochem.2025.104928
en
Elsevier
Validation of the U37K' paleotemperature proxy in the South Brazilian Bight from core-top sediments
article