Environmental and biological controls on Na∕Ca ratios in scleractinian cold-water corals

• Published in: Biogeosciences
• Main Authors: Schleinkofer, Nicolai, Raddatz, Jacek, Freiwald, André, Evans, David, Beuck, Lydia, Rüggeberg, Andres, Liebetrau, Volker
• Format: Text
• Language: English
• Published: 2019
• Subjects: Lophelia pertusa
• Online Access: https://doi.org/10.5194/bg-16-3565-2019; https://www.biogeosciences.net/16/3565/2019/

Here we present a comprehensive attempt to correlate aragonitic Na∕Ca ratios from Desmophyllum pertusum (formerly known as Lophelia pertusa ), Madrepora oculata and a caryophylliid cold-water coral (CWC) species with different seawater parameters such as temperature, salinity and pH. Living CWC specimens were collected from 16 different locations and analyzed for their Na∕Ca ratios using solution-based inductively coupled plasma-optical emission spectrometry (ICP-OES) measurements. The results reveal no apparent correlation with salinity (30.1–40.57 g kg −1 ) but a significant inverse correlation with temperature ( <math xmlns="http://www.w3.org/1998/Math/MathML" id="M6" display="inline" overflow="scroll" dspmath="mathml"><mrow><mo>-</mo><mn mathvariant="normal">0.31</mn><mo>±</mo><mn mathvariant="normal">0.04</mn></mrow></math> <svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="64pt" height="10pt" class="svg-formula" dspmath="mathimg" md5hash="718b24187c65ff9a58780ddd12acf435"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-16-3565-2019-ie00001.svg" width="64pt" height="10pt" src="bg-16-3565-2019-ie00001.png"/></svg:svg> <math xmlns="http://www.w3.org/1998/Math/MathML" id="M7" display="inline" overflow="scroll" dspmath="mathml"><mrow class="unit"><mi mathvariant="normal">mmol</mi><mspace linebreak="nobreak" width="0.125em"/><msup><mi mathvariant="normal">mol</mi><mrow><mo>-</mo><mn mathvariant="normal">1</mn></mrow></msup><msup><mi/><mo>∘</mo></msup><msup><mi mathvariant="normal">C</mi><mrow><mo>-</mo><mn mathvariant="normal">1</mn></mrow></msup></mrow></math> <svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="80pt" height="13pt" class="svg-formula" dspmath="mathimg" md5hash="bd382223e51f2194a62c6c17380164e1"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-16-3565-2019-ie00002.svg" width="80pt" height="13pt" src="bg-16-3565-2019-ie00002.png"/></svg:svg> ). Other marine aragonitic organisms such as Mytilus edulis (inner aragonitic shell portion) and Porites sp. exhibit similar results highlighting the consistency of the calculated CWC regressions. Corresponding Na∕Mg ratios show a similar temperature sensitivity to Na∕Ca ratios, but the combination of two ratios appears to reduce the impact of vital effects and domain-dependent geochemical variation. The high degree of scatter and elemental heterogeneities between the different skeletal features in both Na∕Ca and Na∕Mg , however, limit the use of these ratios as a proxy and/or make a high number of samples necessary. Additionally, we explore two models to explain the observed temperature sensitivity of Na∕Ca ratios for an open and semi-enclosed calcifying space based on temperature-sensitive Na- and Ca-pumping enzymes and transport proteins that change the composition of the calcifying fluid and consequently the skeletal Na∕Ca ratio.