Foraminiferal magnesium in Globeriginoides sacculifer as a paleotemperature proxy

Abstract

Abstract. Foraminiferal magnesium shows increasing promise as a paleothermometer, but the accuracy and precision are limited by biases introduced by partial dissolution, salinity variations, Mg-rich gametogenic calcite, and contaminant phases. We improved cleaning methods and reduced errors introduced by partial dissolution by sampling from well-preserved cores in the equatorial Atlantic and the Caribbean Sea with different dissolution histories. All cores reveal a synchronous 25% increase in Mg/Ca from the stage 2/3 boundary to the Holocene core top, indicating that dissolution is not a controlling factor. Modern temperatures estimated from core top Mg/Ca are 24.5ø-25.0øC, equal to mean annual water temperatures at 50-100 m. We estimate that sea surface temperature increased by 2.6øC (+1.3) from the last glacial maximum to the Holocene. Holocene values were comparable to those during isotope stage 5e. Our data indicate that biases from contaminant p•ses and partial dissolution can be reduced. This paleothermometer holds promise if uncertainties introduced by salinity variations and gametogenic calcite can be constrained.

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

“…Results from G. sacculifer indicate that the LH-LGM SST difference was about 2 1C in the Caribbean Sea and in the eastern equatorial Atlantic Ocean (Hastings et al, 1998;Nu¨rnberg et al, 2000) and nearly 3 1C for the Cariaco basin based on G. ruber (w) . G. ruber (w) results from the eastern tropical Atlantic also show a LH-LGM difference of 2 1C (Elderfield and Ganssen, 2000; this manuscript) but the amplitude is larger (4 1C) further north in the eastern tropical Atlantic (this manuscript).…”

“…Barker and Elderfield, 2002;(3) Barker (this manuscript); (4) Cacho et al (in prep. ); (5) Elderfield and Ganssen, 2000;(6) Hastings et al, 1998;(7) Kiefer et al,in press;(8) Koutavas et al, 2002;(9) Lea et al, 2000;(10) Lea et al, 2003;(11) Mashiotta et al, 1999;(12) Nu¨rnberg et al, 2000;(13) Pahnke et al, 2003;(14) Palmer and Pearson, 2003;(15) Rosenthal et al, 2003;(16) Skinner (unpublished data); (17) Stott et al, 2002;(18) Visser et al, 2003. region (Pelejero et al, 1999;Kienast et al, 2001). In the eastern tropical Pacific just north of the equator, Lea et al (2000) estimated a LH-LGM temperature change of $2.8 1C based on four Mg/Ca records from G. ruber (w).…”

“…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.…”

Biomineralization in perforate foraminifera

“…These physical and chemical variations are the foundation for developing geochemical proxies that quantify environmental changes through time (see Wefer et al, 1999;Zeebe et al, 2008;Katz et al, 2010 for reviews). For example, the magnesium concentration in foraminiferal calcite (Mg/Ca calcite ) varies primarily with seawater temperature (Nürnberg et al, 1996;Lea et al, 1999;Hönisch et al, 2013) and can be used to reconstruct past sea surface (Hastings et al, 1998;Lea et al, 2000) and deep-water (Lear et al, 2000) temperatures. Reliable application of these proxies requires calibration over a wide range of environmental conditions as well as a thorough understanding of the physiological parameters influencing test formation.…”

A method for precise analysis of trace element/calcium ratios in carbonate samples using quadrupole inductively coupled plasma mass spectrometry

“…The concentration of these metals is related to seawater chemistry and environmental parameters. Proxies utilized reconstruct temperature (Mg/Ca) [e.g., Nurnberg et al, 1996;Hastings et al, 1998;Lear et al, 2002], alkalinity and meltwater influx (Ba/Ca) [e.g., Lea, 1993;Lea and Boyle, 1993;Lea and Spero, 1993;Hall and Chan, 2004], seawater chemistry and redox state (U/Ca) [e.g., Russell et al, 1994Russell et al, , 2004, carbonate saturation (Zn/Ca) [e.g., Marchitto et al, 2000] and nutrients (phosphate) (Cd/Ca) [e.g., Boyle and Keigwin, 1985;Boyle, 1988;Bertram et al, 1995;Came et al, 2003]. Cd/Ca and Zn/Ca are of particular importance since they are the key to characterizing distinct water masses.…”