Microbially-mediated and abiotic synthesis of siderite from 10 to
70°C: a new Δ47 and δ18O calibration
Joep v. Dijk1, Alvaro Fernandez1, Inigo A. Müller1, Timoty White2, Mark Lever3 and Stefano M.
Bernasconi1
1
ETH, Geological Institute, Zürich, Switzerland
2
Penn State University, Earth and Environmental Systems Institute, University Park, USA
3
ETH, Department of Environmental Sciences, Zürich, Switzerland
Email: [email protected]
The clumped and oxygen isotope composition of pedogenic siderite (FeCO3) can be
exploited to reconstruct climate in humid continental environments. The only published siderite
Δ47-T calibration [Fernandez et al. 2014] is based on few data points and does not cover the
entire temperature range that can be expected in palaeosols. Furthermore, interlaboratory
discrepancies regarding Δ47-T calibrations are yet to be resolved. For oxygen isotopes, two
calibrations exist. One is derived from abiotic [Carothers et al. 1988] and the other from
microbially-mediated precipitation experiments [Zhang et al. 2001]. These calibration are are
consistent between 45 and 75°C, but but diverge below 33°C and disequilibrium between DIC
and water cannot be ruled out [Zhang et al. 2001]. In this contribution, we present a new siderite
Δ47 and δ18O calibration that was produced by inorganic precipitation through active degassing
and with microbial cultures using the iron reducing bacteria Shewanella Putrefaciens. Our aim
is to cover a temperature range from 10 to 70°C. To promote DIC equilibrium, the enzyme
carbonic anhydrase is used in both active degassing [Fernandez et al. 2014] and bacterial
culture experiments. Experiments between 25 and 35°C will be performed both inorganically
and with bacterial cultures. Siderites were digested offline at 100°C and analyzed with a MAT
253+ isotope ratio mass spectrometer (Thermo Scientific, Bremen, Germany). Δ47 values were
pressure baseline corrected, transferred to the absolute reference frame and projected on an
acid digestion temperature of 25°C [Meckler et al. 2014]. Preliminary results based on 4
precipitation temperatures indicate that the derived Δ47-T calibration has the same temperature
sensitivity as the previously published calibration of Fernandez et al. [2014]. Furthermore, both
Δ47 and δ18O to temperature regressions are highly linear. Δ47 and δ18O fractionation at 30°C is
the same for both abiotic and microbially mediated siderites.
Fernandez, A., Jianwu, T. and Rosenheim, B.E. (2014) Siderite ‘clumped’ isotope thermometry: a new
paleoclimate proxy for humid continental environments. Geochimica et Cosmochimica Acta, 126, 411-421.
Carothers, W. W., Adami, L. H., and Rosenbauer, R. J. (1988). Experimental oxygen isotope fractionation
between siderite-water and phosphoric acid liberated CO2-siderite. Geochimica et Cosmochimica Acta, 52(10),
2445-2450.
Zhang, C. L., Horita, J., Cole, D. R., Zhou, J., Lovley, D. R., and Phelps, T. J. (2001). Temperaturedependent oxygen and carbon isotope fractionations of biogenic siderite. Geochimica et Cosmochimica Acta,
65(14), 2257-2271.
Meckler, A. N., Ziegler, M., Millán, M. I., Breitenbach, S. F., and Bernasconi, S. M. (2014). Long‐term
performance of the Kiel carbonate device with a new correction scheme for clumped isotope measurements.
Rapid Communications in Mass Spectrometry, 28(15), 1705-1715.