The novel hydroxylated tetraether index RI-OH&#8242; as a sea surface temperature proxy for the period 160&#8211;50 ka BP off the Iberian Margin
Authors: Davtian Nina , Bard Edouard , Rostek Frauke , Ménot Guillemette , Darfeuil Sophie 
Published: March 2020

&lt;p&gt;The stable oxygen isotope ratio (&amp;#948;&lt;sup&gt;18&lt;/sup&gt;O) of planktic foraminifers, the C&lt;sub&gt;37&lt;/sub&gt; ketone unsaturation ratio (U&lt;sup&gt;K&amp;#8242;&lt;/sup&gt;&lt;sub&gt;37&lt;/sub&gt;) and the TetraEther indeX of tetraethers consisting of 86 carbon atoms (TEX&lt;sub&gt;86&lt;/sub&gt;) are three well-known examples of paleothermometric proxies. These established proxies are in the realism phase of the Elderfield proxy curve (2002 &lt;em&gt;Geochim. Cosmochim. Acta&lt;/em&gt; 66 Suppl. 1, 213, DOI: 10.1016/S0016-7037(02)01009-8), which means that their advantages and shortcomings are relatively well evidenced, though not fully understood. By contrast, the Ring Index of hydroxylated tetraethers (RI-OH&amp;#8242;) is an example of novel paleothermometer. RI-OH&amp;#8242; is still in the optimism phase, so its potential in paleothermometry remains to be further explored.&lt;/p&gt;&lt;p&gt;Here, we present new high-resolution temperature records over the interval 160&amp;#8211;50 ka BP using four organic proxies (RI-OH&amp;#8242;, RI-OH, TEX&lt;sub&gt;86&lt;/sub&gt; and U&lt;sup&gt;K&amp;#8242;&lt;/sup&gt;&lt;sub&gt;37&lt;/sub&gt;) from three deep-sea sediment cores located in a north-south transect along the Iberian Margin. RI-OH&amp;#8242;, RI-OH and TEX&lt;sub&gt;86&lt;/sub&gt; are based on LC-MS analyses of individual tetraethers with a two-column HPLC and improved mass spectrometric method. We analyzed all organic proxies in the same organic extracts to optimize proxy-proxy comparisons and phase relationship studies.&lt;/p&gt;&lt;p&gt;Our main results strengthen the optimism concerning the novel RI-OH&amp;#8242; proxy for five reasons. 1/, the only existing global core-top calibration to date allows to reconstruct realistic sea surface temperature (SST) from RI-OH&amp;#8242; in comparison to those derived from U&lt;sup&gt;K&amp;#8242;&lt;/sup&gt;&lt;sub&gt;37&lt;/sub&gt; and TEX&lt;sub&gt;86&lt;/sub&gt;. 2/, RI-OH&amp;#8242; allows to establish plausible latitudinal temperature gradients, which are reasonably coherent with those based on U&lt;sup&gt;K&amp;#8242;&lt;/sup&gt;&lt;sub&gt;37&lt;/sub&gt; and TEX&lt;sub&gt;86&lt;/sub&gt;. 3/, RI-OH&amp;#8242; records resemble those from established paleothermometers, especially U&lt;sup&gt;K&amp;#8242;&lt;/sup&gt;&lt;sub&gt;37&lt;/sub&gt; and &amp;#948;&lt;sup&gt;18&lt;/sup&gt;O of planktic foraminifers that better reflect SST than does TEX&lt;sub&gt;86&lt;/sub&gt;. 4/, RI-OH&amp;#8242; responds to Dansgaard-Oeschger and Heinrich events as expected for North Atlantic SST proxies, which supports a direct relationship with Greenland temperature records. 5/, the outputs of a bipolar seesaw model forced with the RI-OH&amp;#8242; record are well correlated with Antarctic paleotemperatures as expected from theoretical considerations.&lt;/p&gt;&lt;p&gt;Overall, our main findings support a continued interest on the novel hydroxylated tetraether paleothermometer RI-OH&amp;#8242; so that it can progress along the Elderfield proxy curve. This work complements our first promising attempt based on a RI-OH record for a shallow core from the western Mediterranean Sea, located in a complex sedimentary setting much less favorable than the Iberian Margin (Davtian et al., 2019 &lt;em&gt;Paleoceanography and Paleoclimatology&lt;/em&gt; 34, 616&amp;#8211;634, DOI: 10.1029/2018PA003452).&lt;/p&gt;