Geochemistry, Geophysics, Geosystems

Effects of temperature on Mg/Ca in neogloboquadrinid shells determined by live culturing

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Abstract

[1] New culturing protocols allowed the development of a Mg/Ca temperature calibration equation for Neogloboquadrina pachyderma (d.). When cultured between 9°C and 19.2°C, Mg/Ca in N. pachyderma (d.) shell calcite exhibits a clear dependence on temperature. Shell calcite Mg/Ca increased exponentially with temperature: Mg/Ca = 0.51−0.15+0.23 * exp(0.10±0.02*T). Limited data suggest N. dutertrei exhibit similar elemental temperature relationships to N. pachyderma (d.). We applied the temperature relationship established by culturing to Mg/Ca in neogloboquadrinid shells collected using plankton tows. Compared to measured SST, the calculated temperatures were within ±2°C for Mg/Ca (95% CI). Multiple samples from single tows generally had calculated temperatures that ranged from near-surface values to temperatures consistent with calcification depths down to ∼70 m. Our work indicates that Mg/Ca temperature calibration equations for temperate and polar foraminiferal species have a similar exponential constant but a higher pre-exponential constant than those for surface-dwelling tropical species. Therefore accurate paleotemperature reconstructions from temperate and polar species require the use of an equation distinct from those used for tropical species.

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