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

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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) = 0.830*exp(0.145*BWT (°C)) for P. wuellerstorfi, and Mg/Ca (mmol/mol) = 0.627*exp(0.143*BWT (°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 = 0.017*d[CO3 2-] -0.14), while dMg/Ca of P. wuellerstorfi is more likely to be governed by TCO2 (dMg/Ca = -0.007*TCO2 + 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.
Median Latitude: -28.834968 * Median Longitude: -19.330520 * South-bound Latitude: -48.013333 * West-bound Longitude: -58.518200 * North-bound Latitude: -1.665000 * East-bound Longitude: 17.755000
Date/Time Start: 1988-03-12T00:00:00 * Date/Time End: 2003-02-27T00:00:00
Minimum DEPTH, sediment/rock: 0.005 m * Maximum DEPTH, sediment/rock: 0.005 m
GeoB1041-1 * Latitude: -3.480000 * Longitude: -7.591667 * Date/Time: 1988-03-12T00:00:00 * Elevation: -4035.0 m * Penetration: 0.42 m * Location: Walvis Ridge * Campaign: M6/6 * Basis: Meteor (1986) * Device: Giant box corer (GKG) * Comment: Karb.-schl., Forams
GeoB1105-3 * Latitude: -1.665000 * Longitude: -12.428330 * Date/Time: 1989-02-25T00:00:00 * Elevation: -3231.0 m * Penetration: 0.36 m * Recovery: 0.32 m * Location: Equatorial Atlantic * Campaign: M9/4 * Basis: Meteor (1986) * Device: Giant box corer (GKG) * Comment: Karbonatschlamm
GeoB1113-7 * Latitude: -5.745000 * Longitude: -11.035000 * Date/Time: 1989-03-02T00:00:00 * Elevation: -2373.0 m * Penetration: 0.35 m * Recovery: 0.25 m * Location: Equatorial Atlantic * Campaign: M9/4 * Basis: Meteor (1986) * Device: Giant box corer (GKG) * Comment: Foram.-sand, tonig
#NameShort NameUnitPrincipal InvestigatorMethodComment
1Event labelEvent
2DEPTH, sediment/rockDepthmGeocode
3Depth, top/minDepth topm
4Depth, bottom/maxDepth botm
5Planulina wuellerstorfi, Magnesium/Calcium ratioP. wuellerstorfi Mg/Cammol/molRaitzsch, MarkusLA-ICP-MS Thermo Finnigan Element 2
6Planulina wuellerstorfi, Magnesium/Calcium ratio, standard deviationP. wuellerstorfi Mg/Ca std dev±Raitzsch, Markus
7Cibicidoides mundulus, Magnesium/Calcium ratioC. mundulus Mg/Cammol/molRaitzsch, MarkusLA-ICP-MS Thermo Finnigan Element 2
8Cibicidoides mundulus, Magnesium/Calcium ratio, standard deviationC. mundulus Mg/Ca std dev±Raitzsch, Markus
246 data points

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