Journal
EARTH AND PLANETARY SCIENCE LETTERS
Volume 438, Issue -, Pages 95-102Publisher
ELSEVIER SCIENCE BV
DOI: 10.1016/j.epsl.2016.01.009
Keywords
benthic foraminiferal Mg/Ca; paleothermometry; Globobulimina ssp.; carbonate ion concentration of pore water; eastern equatorial Atlantic; recostruction of deep sea temperature
Categories
Funding
- NSF [OCE 1260696]
- Directorate For Geosciences [1260696] Funding Source: National Science Foundation
- Division Of Ocean Sciences [1260696] Funding Source: National Science Foundation
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Existing benthic foraminiferal Mg/Ca-temperature calibrations are surrounded by substantial uncertainties mainly due to low temperature sensitivity of Mg/Ca in most benthic foraminifers and the effect of carbonate ion concentration on benthic foraminiferal Mg/Ca. Here we present Mg/Ca analysis of Rose Bengal stained and exceptionally well-preserved tests of the infaunal benthic foraminifer Globobulimina spp. from 39 eastern equatorial Atlantic core top samples. Mg/Ca in Globobulimina spp. varies between 2.5 mmol/mol and 9.1 mmol/mol corresponding to bottom water temperatures (BWT) between 1.8 degrees C and 19.1 degrees C and Delta CO32- pore water between 33.7 +/- 4 and 34.3 +/- 4 mu mol/kg in sediment depths between 1 and 10 cm. Mg/Ca and BWT are linearly correlated with a best fit of Mg/Ca [mmol/mol] = (0.36 +/- 0.02) * BWT [degrees C] + 2.22 +/- 0.19 (r(2) = 0.92, p-value: 11 * 10(-20), and n = 39). Using total alkalinity and pH data of pore water samples from 64 Atlantic multi-corer sites, we obtained Delta CO3pore2- (water) data from the depth habitat range of Globobulimina spp. (>= 1 cm <= 10 cm below sediment surface). We show that Delta CO3pore water2- is significantly lower than and linearly co-varies with the Delta CO32- of the overlying bottom water: Delta CO3pore water2- = (0.67 0.05)*Delta CO3pore2- (water) -(39.84 +/- 1.98); r(2) = 0.75, p-value: 6*10(-20), n = = 64. We found a Mg/Ca sensitivity of 0.009 +/- 0.0044 mmol/mol per mu mol/kg Delta CO3pore2- (water) and Mg/Ca temperature sensitivity of 0.32 +/- 0.06 mmol/mol/ C after a correction for the Delta CO3pore2- (water) effect. This study provides a robust Mg/Ca-temperature calibration, highlights that 6.CO3- pore water is spatially and most likely temporally variable, and contradicts the notion that infaunal foraminiferal Mg/Ca Delta CO3pore2- (water) is relatively immune from Delta CO32- changes in the overlying bottom water. Furthermore, comparison of down core Mg/Ca data of Cibicides pachyderma and Globobulimina spp. demonstrates that the high temperature sensitivity of Mg/Ca in Globobulimina spp. presents a more robust paleothermometer to reconstruct past changes in the thermal state of the deep ocean. (C) 2016 Elsevier B.V. All rights reserved.
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