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

• Main Authors: Schleinkofer, Nicolai, Raddatz, Jacek, Freiwald, Andre, Evans, David, Beuck, Lydia, Rüggeberg, Andres, Liebetrau, Volker
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus Publications (EGU) 2019
• Subjects: Lophelia pertusa
• Online Access: https://oceanrep.geomar.de/id/eprint/45856/; https://oceanrep.geomar.de/id/eprint/45856/13/bg-16-3565-2019.pdf; https://oceanrep.geomar.de/id/eprint/45856/14/bg-16-3565-2019-supplement.pdf; https://doi.org/10.5194/bg-2019-40; https://doi.org/10.5194/bg-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 (−0.31±0.04 mmolmol−1∘C−1). 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.