Dear list members,

I am puzzled about the oxygen fractionation factor between water and
calcite. This fractionation factor is used in palaeoclimatic studies in
order to get palaeotemperatures with uncertainties sometimes better than
0.5 degrees C. However, in the experiments made by Kim and O'Neil 1997
(calcite precipitation from a 5mM bicarbonate solution at 25 degrees C, a
variation of 0.44 permil is observed for the four 1000lnalpha for calcite
considered to be closest to equilibrium. A variation of 0.27 permil was
observed for four selected values in Tarutani et al. (1969). In
palaeotemperature reconstructions this variability approximates a
temperature uncertainty of 1 to 2 degrees C!
Can someone help me out of this?

Thank's

Sophie
Verheyden Sophie
Vrije Universiteit Brussel,
Departement geologie (WE-GISO)
Pleinlaan 2, 1050 Brussel.
T: +32(0)6293388
F: +32(0)6293635