Technical note: No impact of alkenone extraction on foraminiferal stable isotope, trace element and boron isotope geochemistry

<p>Recent advances in geochemical techniques mean that several robust proxies now exist to determine the past carbonate chemistry of the oceans. Foraminiferal <span class="inline-formula"><i>δ</i>¹¹</span>B and alkenone carbon isotopes allow us to reconstruct sea-surface pH and <span class="inline-formula"><i>p</i></span>CO<span class="inline-formula">₂</span>, respectively, and the ability to apply both proxies to the same sediment sample would give strongly paired datasets and reduce sample waste. However, no studies to date have examined whether the solvents and extraction techniques used to prepare alkenones for analysis also impact the geochemistry of foraminifera within those sediments. Here we examine six species pairs of planktic foraminifera, with half being taken from non-treated sediments and half being taken from sediments where alkenones have been extracted. We look for visual signs of contrasting preservation and compare analyses of <span class="inline-formula"><i>δ</i>¹⁸</span>O, <span class="inline-formula"><i>δ</i>¹³</span>C, <span class="inline-formula"><i>δ</i>¹¹</span>B and trace elements (Li, B, Na, Mn, Mg, Sr and <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M7" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><mrow class="chem"><mi mathvariant="normal">U</mi><mo>/</mo><mi mathvariant="normal">Ca</mi></mrow></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="30pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="57892143d10ff0098732657af533175c"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-19-5633-2022-ie00001.svg" width="30pt" height="14pt" src="bg-19-5633-2022-ie00001.png"/></svg:svg></span></span>). We find no consistent geochemical offset between the treatments and excellent agreement in <span class="inline-formula"><i>δ</i>¹¹</span>B measurements between them. Our results show that boron isotope reconstructions of pH in foraminifera from alkenone-extracted sediments can be applied with confidence.</p>