Magnesium/Calcium ratios in benthic foraminifera from surface sediments, supplement to: Raitzsch, Markus; Kuhnert, Henning; Groeneveld, Jeroen; Bickert, Torsten (2008): Benthic foraminifer Mg/Ca anomalies in South Atlantic core top sediments and their implications for paleothermometry. Geochemistry, Geophysics, Geosystems, 9(5), Q05010


We used modern epibenthic foraminifer tests of Cibicidoides mundulus and Planulina wuellerstorfi from South Atlantic core top sediments in order to establish Mg/Ca-temperature relationships for the temperature range from 0 to 15°C. We obtained the following calibrations: Mg/Ca (mmol/mol) = 0.830exp(0.145BWT (°C)) for P. wuellerstorfi, and Mg/Ca (mmol/mol) = 0.627exp(0.143BWT (°C)) for C. mundulus. However, a number of tests, especially those bathed in North Atlantic Deep Water, revealed higher Mg/Ca ratios than predicted from the calibration. Our data suggest that d[CO3 2-] of bottom water exerts a significant control on dMg/Ca (temperature-corrected) of C. mundulus (dMg/Ca = 0.017d[CO3 2-] -0.14), while dMg/Ca of P. wuellerstorfi is more likely to be governed by TCO2 (dMg/Ca = -0.007TCO2 + 15). Since both d[CO3 2-] and TCO2 are closely linked to [CO3 2-], it is inferred that carbonate ion acts as secondary control, after temperature, on benthic shell Mg/Ca below -4°C. A drop in [CO3 2-] by 25 ?mol/kg at 4 km water depth, as suggested for the Last Glacial Maximum, would decrease Mg/Ca by up to 0.4 mmol/mol, which leads to an underestimation of bottom water temperature by -3.5°C. Therefore our results indicate that the Mg/Ca thermometer should be used cautiously for benthic foraminifers where changes in the carbonate chemistry are present in the paleoceanographic record.

Related Identifier
Metadata Access
Creator Raitzsch, Markus; Kuhnert, Henning; Groeneveld, Jeroen; Bickert, Torsten
Publisher PANGAEA - Data Publisher for Earth & Environmental Science
Publication Year 2008
Funding Reference German Science Foundation
Rights Creative Commons Attribution 3.0 Unported;
OpenAccess true
Language English
Resource Type Supplementary Dataset; Dataset
Format text/tab-separated-values
Size 246 data points
Discipline Earth System Research
Spatial Coverage (-58.518W, -48.013S, 17.755E, -1.665N); Walvis Ridge; Equatorial Atlantic; Brazil Basin; Cape Basin; Namibia Continental Margin; Namibia continental slope; Slope off Argentina; Southern Cape Basin; Mid Atlantic Ridge; Vema Channel; Continental slope off Brazil; western South Atlantic; Walvis Bay/Namibia
Temporal Coverage Begin 1988-03-12T00:00:00Z
Temporal Coverage End 2003-02-27T00:00:00Z