Corals Enhance Accuracy in Climate Research

Corals Enhance Accuracy in Climate Research
by Robert Schreiber
Berlin, Germany (SPX) Aug 08, 2024

Understanding Earth's climatic history relies heavily on accurate temperature reconstructions from ancient oceans. Traditionally, these reconstructions have been derived from the ratios of oxygen isotopes in the calcium carbonate of fossils. However, this method faces significant challenges due to biological processes known as "vital effects," particularly pronounced in corals, which can skew the data. A team led by the University of Gottingen has now demonstrated how the presence of a rare third oxygen isotope can distinguish between temperature influences and biological effects. Their findings are published in *Geochemical Perspective Letters*.

Coral skeletons, composed of calcium carbonate, selectively incorporate different oxygen isotopes, some lighter and some heavier. Typically, at lower water temperatures, more of the heavier oxygen isotope (oxygen-18) is incorporated. Scientists use the ratios of oxygen-18 to the lighter oxygen-16 to estimate ancient seawater temperatures. However, biological processes can alter these ratios, leading to incorrect temperature readings. The researchers discovered that the rare oxygen-17 isotope can correct for these biological influences, allowing for more precise historical temperature reconstructions and insights into coral biomineralization.

Dr. David Bajnai from Gottingen University's Geoscience Centre explained, "We used corals for our study as we know quite a lot about the processes by which they grow their skeletons. We are excited to apply this concept to other organisms commonly used in the study of Earth's past climate. We hope that triple oxygen isotope analyses will open up previously unusable datasets for paleoclimate research, enabling more accurate climate reconstructions, going further back in time."

Professor Daniel Herwartz from Ruhr University Bochum added, "We were also able to show that triple oxygen isotope analyses can inform us about the various processes we collectively call 'vital effects'. For corals, we can now confirm that the main process involved is related to a chemical process called CO2 absorption, which we have independently studied in experiments. Such advanced techniques help to gain new insights into how organisms build their harder structures."

These measurements of the oxygen-17 isotope, referred to as the triple oxygen isotope method, are complex and conducted by only a few labs worldwide, including the stable isotope laboratory at Gottingen University, which utilizes advanced tuneable diode laser absorption spectroscopy.

Research Report:Correcting for vital effects in coral carbonate using triple oxygen isotopes