Exact climate data from the past
Innovative method opens up new perspectives for reconstructing climatic conditions of past eras

Date:
August 10, 2020
Source:
Goethe University Frankfurt
Summary:
Corals and cave carbonates can reveal the temperatures that
prevailed at the Earth's surface at the time they formed. An
international team of geoscientists has developed a new method
that makes it possible to identify whether the composition of
these deposits was exclusively controlled by temperature, or if
the formation process itself exerted an additional control. The
new method allows scientists to determine past Earth surface
temperatures more reliably.



FULL STORY ========================================================================== Corals precipitate their calcareous skeletons (calcium carbonate)
from seawater. Over thousands of years, vast coral reefs form due
to the deposition of this calcium carbonate. During precipitation,
corals prefer carbonate groups containing specific variants of oxygen
(chemical symbol: O). For example, the lower the water temperature, the
higher the abundance of a heavy oxygen variant, known as isotope 18O,
within the precipitated carbonate.

Unfortunately, the 18O abundance of the seawater also influences the
abundance of 18O in the calcium carbonate -- and the contribution of 18O
from seawater cannot be resolved when determining temperatures based on carbonate 18O abundances alone.


==========================================================================
A great step forward was the discovery that the isotopic composition of
the precipitated carbonate allows temperature determinations independent
of the composition of the water if the abundance of a specific, very
rare carbonate group is measured. This carbonate group contains two heavy isotopes, a heavy carbon isotope (13C) and a heavy oxygen isotope (18O)
which are referred to as "clumped isotopes." Clumped isotopes are more
abundant at lower temperatures.

However, even with this method there was still a problem: The
mineralization process itself can affect the incorporation of heavy
isotopes in the calcium carbonate (kinetic effects). If unidentified, the
bias introduced by such kinetic effects leads to inaccurate temperature determinations. This particularly applies for climatic archives like
corals and cave carbonates.

An international research group led by Professor Jens Fiebig at the
Department of Geosciences at Goethe University Frankfurt has now found a solution to this problem. They have developed a highly sensitive method
by which -- in addition to the carbonate group containing 13C and 18O --
the abundance of another, even rarer carbonate group can be determined
with very high precision. This group also contains two heavy isotopes,
namely two heavy oxygen isotopes (18O).

If the theoretical abundances of these two rare carbonate groups are
plotted against each other in a graph, the influence of the temperature
is represented by a straight line. If, for a given sample, the measured abundances of the two heavy carbonate groups produce a point away
from the straight line, this deviation is due to the influence of the mineralization process.

David Bajnai, Fiebig's former PhD student, applied this method to various climatic archives. Among others, he examined various coral species, cave carbonates and the fossil skeleton of a squid-like cephalopod (belemnite).

Today, Dr. Bajnai is a post-doctoral researcher at the University
of Cologne.

He explains: "We were able to show that -- in addition to temperature --
the mechanisms of mineralization also greatly affect the composition of
many of the carbonates that we examined. In the case of cave carbonates
and corals, the observed deviations from the exclusive temperature
control confirm model calculations of the respective mineralization
processes conducted by Dr. Weifu Guo, our collaborator at the Woods Hole Oceanographic Institution in the USA.

The new method, for the first time, makes it possible to quantitatively
assess the influence of the mineralization process itself. This way,
the exact temperature of carbonate formation can be determined."
Professor Jens Fiebig is convinced that the new method holds great
potential: "We will further validate our new method and identify climatic archives that are particularly suitable for an accurate and highly precise reconstruction of past Earth surface temperatures. We also intend to use
our method to study the effect that anthropogenic ocean acidification
has on carbonate mineralization, for instance in corals. The new method
might even allow us to estimate the pH values of earlier oceans." If
all this succeeds, the reconstruction of environmental conditions that prevailed throughout Earth's history could be greatly improved, he adds.


========================================================================== Story Source: Materials provided by Goethe_University_Frankfurt. Note:
Content may be edited for style and length.


========================================================================== Journal Reference:
1. David Bajnai, Weifu Guo, Christoph Spo"tl, Tyler B. Coplen,
Katharina
Methner, Niklas Lo"ffler, Emilija Krsnik, Eberhard Gischler,
Maximilian Hansen, Daniela Henkel, Gregory D. Price, Jacek Raddatz,
Denis Scholz, Jens Fiebig. Dual clumped isotope thermometry
resolves kinetic biases in carbonate formation temperatures. Nature
Communications, 2020; 11 (1) DOI: 10.1038/s41467-020-17501-0 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/08/200810103237.htm

--- up 3 weeks, 5 days, 1 hour, 55 minutes
* Origin: -=> Castle Rock BBS <=- Now Husky HPT Powered! (1337:3/111)