New insight from Great Barrier Reef coral provides correction factor to climate records

ScienceDaily | 6/18/2019 | Staff
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The new findings are reported in the journal Frontiers in Marine Science.

For over 500 million years, corals have been passively keeping track of changing sea-surface temperature by recording the ratio of calcium to strontium and oxygen isotopes within their skeletons, the researchers said. The coral skeletons -- which are made of calcium carbonate mineral -- grow layers like tree rings that have increased amounts of strontium and the lighter isotope of oxygen during the warmer season. Climate scientists take advantage of this process to track sea surface temperature through time.

Climate-tracking - Technique - Flaws - University - Illinois

However, this climate-tracking technique is not without its flaws, said University of Illinois geology and microbiology professor Bruce Fouke, who led the new research.

"We can ground truth coral-based sea-surface temperature records against records made using temperature probes," Fouke said, "Remarkably, the coral records are accurate most of the time, but there are instances where measurements have been off by as much as nine degrees Celsius, and this needs to be rectified."

Skeletons - Polyps - Deposit - Aragonite - Mineral

To grow their skeletons, coral polyps deposit aragonite. However, the mineral also crystalizes from seawater, the researchers said, and that can cause problems when analyzing the original coral skeleton chemistry. As seawater flows through the porous coral structure, it deposits newly crystalized aragonite on top of skeletons. That new aragonite, which may record a different sea-surface temperature, alters original skeletal chemistry through a process called diagenesis, Fouke said.

"It is difficult to tell the diagenetic aragonite from the original coral skeleton without using high-powered microscopes," said Kyle Fouke, a Bucknell University undergraduate student, Carl R. Woese Institute for Genomic Biology affiliate and co-author of the study. "It is also challenging to know exactly when the diagenetic alteration took place -- days or decades after the skeletons were formed. Unless you are using the newest microscopy techniques to help select your samples, you...
(Excerpt) Read more at: ScienceDaily
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