REEVALUATION OF MG/CA-TEMPERATURE CALIBRATION IN GLOBIGERINOIDES RUBER: A SEDIMENT TRAP APPROACH

Planktonic foraminiferal Mg/Ca is one of the most widely-applied proxies for sea surface temperature reconstructions. Current calibrations yield a temperature sensitivity of 9.0 ± 1.0% Mg/Ca per °C (1-2). Recent studies suggest, however, that these estimates may be additionally influenced by salinity. Culture experiments suggest 3.3±1.7% increase in Mg/Ca per salinity unit (3), substantially lower than controversial evidence of 27±4% (4).

Here we present a paired Mg/Ca and δ¹⁸O study in Globigerinoides ruber (sensu lato, 250-350µm) from sediment trap samples from the Hawaii Ocean Time Series. Within the habitat depth range of G. ruber(0-25 m), seasonal temperature and salinity vary by 4 °C and 0.7 practical salinity units, respectively. The relatively small seasonal changes in salinity allow us to isolate and quantify the temperature effect on Mg/Ca using spatially and temporally high-resolved temperature measurements. Our study shows an exponential Mg/Ca-temperature relationship of:

Mg/Ca [mmol/mol] = (0.92 ± 0.35)exp((0.065 ± 0.015)*T[˚C]) (RMSE=0.31).

Multivariate regression incorporating both temperature and salinity does not reveal a significant salinity influence on our data; the temperature sensitivity of the multivariate fit agrees within error with the above (T-only) equation. Our results indicate a temperature sensitivity of 6.5 ± 1.5% Mg/Ca per °C that is in agreement, within error, with the results of a culture-based study that accounts for salinity effect (5), supporting the emerging notion that the temperature influence on Mg/Ca may be lower than the canonical 9% per °C value (1-2).

1. Anand et al., Paleoceanography, 18, 1050 (2003); 2. Dekens et al., G³ 3, 1022 (2002); 3. Hönisch et al., GCA, 121, 196-213 (2013); 4. J. Arbuszewski et al., EPSL, 300, 185-196 (2010); 5. Kisakürek et al., EPSL, 273, 260–269 (2008).