Coupled Mg/Ca and clumped isotope analyses of foraminifera provide consistent water temperatures. (1st September 2018)

• Record Type: Journal Article
• Authors: Breitenbach, Sebastian F.M.; Mleneck-Vautravers, Maryline J.; Grauel, Anna-Lena; Lo, Li; Bernasconi, Stefano M.; Müller, Inigo A.; Rolfe, James; Gázquez, Fernando; Greaves, Mervyn; Hodell, David A.
• Is Part Of: Geochimica et cosmochimica acta. Volume 236(2018)
• Page Start: 283
• Page End: 296
• Publication Date: 2018-09-01
• Subjects: Clumped isotopes -- Mg/Ca analysis -- Planktonic foraminifera -- Paleoceanography -- Paleoclimatology; Geochemistry -- Periodicals; Meteorites -- Periodicals; Géochimie -- Périodiques; Météorites -- Périodiques; Geochemie; Astrochemie; Electronic journals; 551.905
• DOI: 10.1016/j.gca.2018.03.010
• Languages: English
• ISSNs: 0016-7037

Abstract

Abstract: The reliable determination of past seawater temperature is fundamental to paleoclimate studies. We test the robustness of two paleotemperature proxies by combining Mg/Ca and clumped isotopes ( Δ 47 ) on the same specimens of core top planktonic foraminifera. The strength of this approach is that Mg/Ca and Δ 47 are measured on the same specimens of foraminifera, thereby providing two independent estimates of temperature. This replication constitutes a rigorous test of individual methods with the advantage that the same approach can be applied to fossil specimens. Aliquots for Mg/Ca and clumped analyses are treated in the same manner following a modified cleaning procedure of foraminifera for trace element and isotopic analyses. We analysed eight species of planktonic foraminifera from coretop samples over a wide range of temperatures from 2 to 29°C. We provide a new clumped isotope temperature calibrations using subaqueous cave carbonates, which is consistent with recent studies. Tandem Mg/Ca– Δ 47 results follow an exponential curve as predicted by temperature calibration equations. Observed deviations from the predicted Mg/Ca- Δ 47 relationship are attributed to the effects of Fe-Mn oxide coatings, contamination, or dissolution of foraminiferal tests. This coupled approach provides a high degree of confidence in temperature estimates when Mg/Ca and Δ 47 yield concordant results, and can be used to infer the past δ 18 O of seawater (δ 18 Osw ) for paleoclimate studies.