Past temperature and δ18O of surface ocean waters inferred from foraminiferal Mg/Ca ratios

Abstract

Determining the past record of temperature and salinity of ocean surface waters is essential for understanding past changes in climate, such as those which occur across glacial-interglacial transitions. As a useful proxy, the oxygen isotope composition (delta18O) of calcite from planktonic foraminifera has been shown to reflect both surface temperature and seawater delta18O, itself an indicator of global ice volume and salinity. In addition, magnesium/calcium (Mg/Ca) ratios in foraminiferal calcite show a temperature dependence due to the partitioning of Mg during calcification. Here we demonstrate, in a field-based calibration experiment, that the variation of Mg/Ca ratios with temperature is similar for eight species of planktonic foraminifera (when accounting for Mg dissolution effects). Using a multi-species record from the Last Glacial Maximum in the North Atlantic Ocean we found that past temperatures reconstructed from Mg/Ca ratios followed the two other palaeotemperature proxies: faunal abundance and alkenone saturation. Moreover, combining Mg/Ca and delta18O data from the same faunal assemblage, we show that reconstructed surface water delta18O from all foraminiferal species record the same glacial-interglacial change--representing changing hydrography and global ice volume. This reinforces the potential of this combined technique in probing past ocean-climate interactions.

Effect of salinity and seawater calcite saturation state on Mg and Sr incorporation in cultured planktonic foraminifera

“…Overall the test carbonate of G. sacculifer has lower Mg/Ca ratios (this study; Nürnberg et al, 1996b;Anand et al, 2003) compared to O. universa and Globigerinoides bulloides Elderfield and Ganssen, 2000;McConnell and Thunell, 2005;Russell et al, 2004). Mg/Ca ratios in the tests of G. sacculifer and Globigerinoides ruber (white) (Kısakürek et al, 2008) show similar values ( Fig.…”

“…2A) (Nürnberg et al, 1996b;Lea et al, 1999;Elderfield and Ganssen, 2000;Anand et al, 2003;Russell et al, 2004;McConnell and Thunell, 2005;Kısakürek et al, 2008). All these calibrations show an increase in the incorporation of Mg into foraminiferal test carbonate with increasing temperatures.…”

“…Accuracy for each individual analysis was calculated using the Glitter computer program, which we also used to calculate elemental concentrations (Glitter, LA-ICP/MS Data Reduction and Display, GEMOC, CSIRO, Maquarie Research Limited, 1999-2000. The intervals of the acquired data used to calculate concentrations were selected avoiding sections with high Al and/or Pb counts.…”

Holocene and Eemian sea surface temperature trends as revealed by alkenone and Mg/Ca paleothermometry

“…Complications arise when species-specific ecological behaviour is considered, although it also provides the opportunity to further investigate temperature changes across a wide range of foraminifera growth seasons and water depths (Elderfield and Ganssen, 2000).…”

Planktonic foraminiferal Mg/Ca as a proxy for past oceanic temperatures: a methodological overview and data compilation for the Last Glacial Maximum

“…More recently Mg/Ca thermometry has been greatly refined and applied almost routinely to paleoceanographic questions concerning temperature variability through time (e.g. Nu¨rnberg et al, 1996;Hastings et al, 1998;Lea et al, 1999Lea et al, , 2000Lea et al, , 2002Mashiotta et al, 1999;Elderfield and Ganssen, 2000;Rosenthal et al, 2000;Koutavas et al, 2002;Stott et al, 2002;Pahnke et al, 2003;Rosenthal et al, 2003;Visser et al, 2003). Mg/ Ca ratios of other calcifying organisms have also been shown to be sensitive to changes in temperature.…”