Oxygen isotope composition of waters recorded in carbonates in strong clumped and oxygen isotopic disequilibrium
<p>Paleoenvironmental reconstructions, which are mainly retrieved from oxygen isotope (<span class="inline-formula"><i>δ</i><sup>18</sup>O</span>) and clumped isotope (<span class="inline-formula">Δ<sub>47</sub></span...
Main Authors: | , , , , |
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Format: | Article |
Language: | English |
Published: |
Copernicus Publications
2020-04-01
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Series: | Biogeosciences |
Online Access: | https://www.biogeosciences.net/17/1731/2020/bg-17-1731-2020.pdf |
Summary: | <p>Paleoenvironmental reconstructions, which are mainly retrieved
from oxygen isotope (<span class="inline-formula"><i>δ</i><sup>18</sup>O</span>) and clumped isotope (<span class="inline-formula">Δ<sub>47</sub></span>) 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
<span class="inline-formula"><i>δ</i><sup>18</sup>O</span> and <span class="inline-formula">Δ<sub>47</sub></span> offsets from isotopic equilibrium
values is largely overlooked. Additionally, in carbonates formed in isotopic
equilibrium, the use of the carbonate <span class="inline-formula"><i>δ</i><sup>18</sup>O</span> signature as a
paleothermometer relies on our knowledge of the paleowaters' <span class="inline-formula"><i>δ</i><sup>18</sup>O</span> value, which is often assumed. Here, we report the largest <span class="inline-formula">Δ<sub>47</sub></span> offsets observed to date (as much as <span class="inline-formula">−0.270</span> ‰),
measured on microbial carbonates that are strongly linked to carbonate
<span class="inline-formula"><i>δ</i><sup>18</sup>O</span> offsets (<span class="inline-formula">−25</span> ‰) from equilibrium.
These offsets are likely both related to the microorganism metabolic
activity and yield identical erroneous temperature reconstructions.
Unexpectedly, we show that the <span class="inline-formula"><i>δ</i><sup>18</sup>O</span> value of the water in which
carbonates precipitated, as well as the water–carbonate <span class="inline-formula"><i>δ</i><sup>18</sup>O</span>
fractionation dependence on temperature at equilibrium, can be retrieved from
these paired <span class="inline-formula"><i>δ</i><sup>18</sup>O</span> and <span class="inline-formula">Δ<sub>47</sub></span> disequilibrium values
measured in carbonates. The possibility to retrieve the <span class="inline-formula"><i>δ</i><sup>18</sup>O</span>
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.</p> |
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ISSN: | 1726-4170 1726-4189 |