Controls on shell Mg/Ca and Sr/Ca in cultured planktonic foraminiferan, Globigerinoides ruber (white) |
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| Authors: | B K&#x;sakürek A Eisenhauer F Bhm D Garbe-Schnberg J Erez |
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| Institution: | aLeibniz-Institute of Marine Sciences, IFM-GEOMAR, Wischhofstr. 1-3, 24148 Kiel, Germany;bChristian-Albrechts University of Kiel, Ludewig-Meyn-Straße 10, 24118 Kiel, Germany;cInstitute of Earth Sciences, The Hebrew University, Givat Ram, Jerusalem, 91904, Israel |
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| Abstract: | Mg/Ca and Sr/Ca ratios were determined on a single species of planktonic foraminiferan, Globigerinoides ruber (white), collected from the Gulf of Eilat and cultured in seawater at five different salinities (32 to 44), five temperatures (18 to 30 °C) and four pH values (7.9 to 8.4). The Mg/Ca-temperature calibration of cultured G. ruber (with an exponential slope of 8 ± 3%/°C) agrees well with previously published calibrations from core-tops and sediment traps. However, the dependence of Mg/Ca on salinity (with an exponential slope of 5 ± 3%/psu) is also significant and should be included in the calibration equation. With this purpose, we calculated a calibration equation for G. ruber dependent on both temperature and salinity within the 95% confidence limits:Mg/Ca(mmol/mol)=exp0.06(±0.02)*S(psu)+0.08(±0.02)*T(°C)−2.8(±1.0)],R2=0.95 | The influence of pH on Mg/Ca ratios is negligible at ambient seawater pH (8.1 to 8.3). However, we observe a dominating pH control on shell Mg/Ca when the pH of seawater is lower than 8.0. Sr/Ca in G. ruber shows a significant positive correlation with average growth rate. Presumably, part of the variability in shell Sr/Ca in the geological record is linked to changes in growth rates of foraminifera as a response to changing environmental conditions.
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| Keywords: | planktonic foraminifera Mg/Ca Sr/Ca salinity temperature pH growth rate culturing |
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