Abstract. Paleoenvironmental reconstructions, which are mainly retrieved
from oxygen isotope (δ18O) and clumped isotope (Δ47) compositions of carbonate minerals, are compromised when carbonate
precipitation occurs in isotopic disequilibrium. To date, knowledge of
these common isotopic disequilibria, known as vital effects in biogenic
carbonates, remains limited, and the potential information recorded by
δ18O and Δ47 offsets from isotopic equilibrium
values is largely overlooked. Additionally, in carbonates formed in isotopic
equilibrium, the use of the carbonate δ18O signature as a
paleothermometer relies on our knowledge of the paleowaters' δ18O value, which is often assumed. Here, we report the largest Δ47 offsets observed to date (as much as −0.270 ‰),
measured on microbial carbonates that are strongly linked to carbonate
δ18O offsets (−25 ‰) from equilibrium.
These offsets are likely both related to the microorganism metabolic
activity and yield identical erroneous temperature reconstructions.
Unexpectedly, we show that the δ18O value of the water in which
carbonates precipitated, as well as the water–carbonate δ18O
fractionation dependence on temperature at equilibrium, can be retrieved from
these paired δ18O and Δ47 disequilibrium values
measured in carbonates. The possibility to retrieve the δ18O
value of paleowaters, sediments' interstitial waters or organisms' body
water at the carbonate precipitation loci, even from carbonates formed in
isotopic disequilibrium, opens long-awaited research avenues for both
paleoenvironmental reconstructions and biomineralization studies.
Supplementary material to "Non-destructive estimates of soil carbonic anhydrase activity and soil
water oxygen isotope composition"
