A culture-based calibration of benthic foraminiferal paleotemperature proxies: δ<sup>18</sup>O and Mg/Ca results

Abstract

Abstract. Benthic foraminifera were cultured for five months at four temperatures (4, 7, 14 and 21 °C) to establish the temperature dependence of foraminiferal δ18O and Mg/Ca. Two Bulimina species (B. aculeata and B. marginata) were most successful, adding chambers at all four temperatures and reproducing at 7 and 14 °C. Foraminiferal δ18O values displayed ontogenetic variations, with lower values in younger individuals. The δ18O values of adult specimens decreased with increasing temperature in all but the 4 °C treatment, exhibiting a relationship consistent with previous δ18O paleotemperature calibration studies. Foraminiferal Mg/Ca values, determined by laser ablation inductively coupled plasma mass spectrometry, were broadly consistent with previous Mg/Ca calibration studies, but extremely high values in the 4 °C treatment and higher than expected values at two of the other three temperatures make it challenging to interpret these results.

Variability in calcitic Mg/Ca and Sr/Ca ratios in clones of the benthic foraminifer Ammonia tepida

“…5). This is in contrast with a number of reports on sizespecific Mg/Ca ratios in other species of benthic foraminifera from culturing experiments (Hintz et al, 2006;Filipsson et al, 2010;Diz et al, 2012). Discrepancies between studies could stem from speciesspecific differences in controls on element incorporation, sample size, or both.…”

“…Spero and Lea, 1996;Bijma et al, 1998). Using newborn clones (Section 2.1; Hintz et al, 2006;McCorkle et al, 2008;Filipsson et al, 2010;Barras et al, 2010;Diz et al, 2012) circumvents the inaccuracies associated with such manipulations and allows analysis of the smallest foraminifer size fractions. Moreover, using LA-ICP-MS, the full range of chamber sizes can be analyzed for elements with sufficiently high concentrations (e.g.…”

“…Previous work suggested that ontogenetic (i.e. life-stage related) changes can be responsible for intra-and inter-test Mg/Ca variability in benthic foraminifera (Hintz et al, 2006;Filipsson et al, 2010;Raitzsch et al, 2011a;Diz et al, 2012). Ontogeny can affect trace element partitioning through changes in physiology, growth rate or changes in surface area-volume ratios.…”

Modelling δ13C in benthic foraminifera: Insights from model sensitivity experiments

“…Since it is notoriously difficult to culture deep-sea benthic foraminifera in the laboratory under insitu conditions, culture experiments are often limited to shallowwater species (Chandler et al, 1996), or specimen taken from water depths shallower than 250 m (Wilson-Finelli et al, 1998;Havach et al, 2001). Culturing systems like those developed by Hintz et al (2004) have allowed for systematic experiments on deep sea benthic foraminifera (Nomaki et al, 2005(Nomaki et al, , 2006McCorkle et al, 2008;Barras et al, 2010;Filipsson et al, 2010). From a theoretical point of view, progress has mostly been made on planktonic foraminifera Zeebe et al, 1999).…”

Inductively coupled plasma- and glow discharge plasma-sector field mass spectrometry : Part II. Applications

“…172 Sea water temperatures can be calculated from Mg/Ca ratios in foraminifera since the uptake of Mg into foraminiferal CaCO 3 is temperature-dependent. [173][174][175] Katz et al measured Mg/Ca ratios of benthic foraminifera by ICP-SFMS to calculate seafloor water temperatures and to reconstruct the stepwise transition from the Eocene greenhouse to the Oligocene icehouse. 174 Oppo et al used Mg/Ca ratios of foraminifera for 2000-year-long sea water temperature reconstructions.…”