Modifications in Ocean Chemistry Reveal How Sea Ranges Have an effect on the International Carbon Cycle – Watts Up With That?

New analyzes of strontium isotopes show how the global carbon cycle has responded to changes in climate and sea level over geological time

UNIVERSITY OF CALIFORNIA – SANTA CRUZ

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PICTURE: These figures show how changes in sea level affect the deposition of hydrocarbons and other processes in the global carbon cycle. View More CREDIT: ILLUSTRATIONS BY MADDISON WOOD

A new analysis of strontium isotopes in marine sediments has enabled scientists to reconstruct fluctuations in ocean chemistry that are related to changing climatic conditions over the past 35 million years.

The results, published in Science on March 26, offer new insights into the inner workings of the global carbon cycle and, in particular, the processes by which carbon is removed from the environment through deposition of carbonates.

“Strontium is very similar to calcium and is therefore incorporated into the calcium carbonate shells of marine organisms,” explained lead author Adina Paytan, research professor at the UC Santa Cruz Institute of Marine Sciences.

Paytan and her co-authors studied the ratios of various strontium isotopes, including radiogenic isotopes (produced by radioactive decay) and stable isotopes, which provide supplementary information about geochemical processes. They found that the stable isotope ratio of strontium in the ocean has changed significantly over the past 35 million years and is still changing today, implying large changes in the concentration of strontium in seawater.

“It’s not in a stable state, so what goes in the ocean and what goes don’t go together,” Paytan said. “The composition of strontium in seawater changes depending on how and where carbonates are deposited, and this is affected by changes in sea level and climate.”

The fluctuations in strontium isotope ratios analyzed in this study reflect the combined effect of shifts in the global equilibrium of geological processes, including onshore rock weathering, hydrothermal activity, and the formation of carbonate sediments in both deep-sea and shallow marine environments.

The carbonate deposition in the open ocean is carried out by marine plankton such as coccolithophores and foraminifera, which form their shells from the calcium carbonate mineral calcite. Hard corals are more common in shallow water on the continental shelf and form their skeletons from another calcium carbonate mineral, aragonite, which contains more strontium than calcite.

“When corals form, they remove strontium, and when they are exposed, that strontium is washed out and goes back into the ocean,” Paytan said. “As sea level changes, the continental shelf on which corals grow is more or less exposed, which affects the strontium composition of the seawater.”

The carbonate deposit is also returned to the climate system as the ocean absorbs carbon dioxide from the atmosphere and the carbonate deposit removes carbon from the system on geological time scales. The global carbon cycle and atmospheric carbon dioxide are closely linked to climate change over the long term as well as during the recurring ups and downs of the recent Ice Age cycles.

“The new kind of information we can read from the stable isotopes of strontium now allows us to look more closely at the business end of the global carbon cycle as carbon is removed from the environment and dumped in marine carbonate beds,” said co-author Mathis Hain , Assistant Professor of Earth and Planetary Sciences at UCSC.

“These results open a new window in which we can see how the global carbon cycle has adapted to sea levels and climate change over geological time,” he added. “We will need this knowledge to guide our response to our current climate emergency and to mitigate the worst effects of ocean acidification.”

Researchers were able to reconstruct a robust and detailed record of strontium isotope variations in seawater based on an analysis of marine barite extracted from deep-sea sediment cores.

“Records like this are critical to understanding how our earth works in geological time,” said Ohio State University co-author Elizabeth Griffith. “Our international team worked together to create this unique record and explain its meaning through mathematical modeling so that we could reconstruct past changes when climatic conditions were different. The hope is to get a glimpse of how our blue planet might function in the future. “

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In addition to Paytan, Hain and Griffith, Anton Eisenhauer and Klaus Wallmann from GEOMAR Helmholtz Center for Ocean Research in Germany and Andrew Ridgwell from UC Riverside are co-authors of the work. This work was supported by the National Science Foundation.

From EurekAlert!

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