Understanding the deglacial relationship between carbon isotopes and temperature in stalagmites from Western Europe
Authors: Lechleitner Franziska A. , Day Christopher C. , Wilhelm Micah , Haghipour Negar , Kost Oliver , Henderson Gideon M. , Stoll Heather M. 
Published: March 2020

&lt;p&gt;The last deglaciation was a period of rapid and profound climatic change in Western Europe. Speleothem carbon isotope (&amp;#948;&lt;sup&gt;13&lt;/sup&gt;C) records from mid-latitude Western Europe have consistently shown large and reproducible excursions over this time period, strikingly similar to available temperature reconstructions from other archives. The mechanism behind the temperature sensitivity of speleothem &amp;#948;&lt;sup&gt;13&lt;/sup&gt;C, however, remains poorly constrained, due to the complex interplay of multiple processes affecting this proxy.&lt;/p&gt;&lt;p&gt;Here we use a multi-proxy approach and forward modelling of karst processes to investigate what drives the response of speleothem &amp;#948;&lt;sup&gt;13&lt;/sup&gt;C to the last deglaciation in Western Europe. We present new proxy data (&lt;sup&gt;14&lt;/sup&gt;C and &amp;#948;&lt;sup&gt;44&lt;/sup&gt;Ca) from speleothem Candela from El Pindal Cave, northern Spain, which covers the period from the Last Glacial Maximum (25 ka BP) to the Early Holocene (8 ka BP). Previously published stable isotope data (Moreno et al., 2010) revealed a pronounced decrease in &amp;#948;&lt;sup&gt;13&lt;/sup&gt;C over the deglaciation (~8&amp;#8240; VPDB) which closely tracks regional temperature records from the Iberian Margin. We make use of the different sensitivities of ancillary proxies (&lt;sup&gt;14&lt;/sup&gt;C, Mg/Ca, and &amp;#948;&lt;sup&gt;44&lt;/sup&gt;Ca) to processes in soil and karst to quantify their relative importance on the &amp;#948;&lt;sup&gt;13&lt;/sup&gt;C shift. For this, we use the forward modelling software CaveCalc (Owen et al., 2018) to generate a large ensemble of possible solutions, from which the ones closest matching the data are chosen and evaluated.&lt;/p&gt;&lt;p&gt;Our preliminary results suggest that in-cave and karst processes (carbonate host rock dissolution and reprecipitation) cannot explain the full amplitude of the &amp;#948;&lt;sup&gt;13&lt;/sup&gt;C shift over the deglaciation, and that changes in soil &amp;#948;&lt;sup&gt;13&lt;/sup&gt;C are to some extent translated to the speleothem carbonate &amp;#948;&lt;sup&gt;13&lt;/sup&gt;C. The possibility of quantitatively disentangling processes in the soil from other karst processes could allow the reconstruction of past soil activity from speleothems.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;References:&lt;/p&gt;&lt;p&gt;Moreno, A., Stoll, H., Jim&amp;#233;nez-S&amp;#225;nchez, M., Cacho, I., Valero-Garc&amp;#233;s, B., Ito, E., Edwards, R.L., 2010. A speleothem record of glacial (25-11.6 kyr BP) rapid climatic changes from northern Iberian Peninsula. Glob. Planet. Change 71, 218&amp;#8211;231. doi:10.1016/j.gloplacha.2009.10.002&lt;/p&gt;&lt;p&gt;Owen, R.A., Day, C.C., Henderson, G.M., 2018. CaveCalc: A new model for speleothem chemistry &amp; isotopes. Comput. Geosci. doi:10.1016/J.CAGEO.2018.06.011&lt;/p&gt;