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Ancient Deep-Sea Corals Could Offer Insights into Effect of Ocean on Rising CO2 Levels

According to a new study performed by the Universities of Bristol, St Andrews, and Nanjing, the fossilized remains of ancient deep-sea corals may serve as time machines that offer a new understanding of the effect the ocean has on the ever-increasing CO2 levels.

Analysis of the fossil remains of deep-sea corals (pictured here) was used to examine the history of the oceans and connections to the global climate. Image Credit: Dann Blackwood, USGS.

The study was published in the Science Advances journal. Increasing CO2 levels played a vital role in ending the last ice age; however, the reason for this increase in CO2 has confused researchers for decades.

An international research group has used geochemical fingerprinting of fossil corals and identified new proof that this CO2 increase was related to extremely quick changes in ocean circulation near Antarctica.

The researchers gathered the fossil remains of deep-sea corals that survived thousands of meters below the waves. They analyzed the radioactive decay of the minuscule amounts of uranium found in such skeletons and identified the corals that grew at the end of the ice age approximately 15,000 years ago.

Additional geochemical fingerprinting of such specimens—such as measurements of radiocarbon—enabled the researchers to remodel changes in ocean circulation and match them to variations in the global climate at an unparalleled time resolution.

The data show that deep ocean circulation can change surprisingly rapidly, and that this can rapidly release CO2 to the atmosphere.

Laura Robinson, Study Lead and Professor of Geochemistry, School of Earth Sciences, University of Bristol

According to Dr. James Rae at St Andrew’s School of Earth and Environmental Sciences, “The corals act as a time machine, allowing us to see changes in ocean circulation that happened thousands of years ago. They show that the ocean around Antarctica can suddenly switch its circulation to deliver burps of CO2 to the atmosphere.”

Researchers worldwide have presumed that the Southern Ocean helped much in ending the last ice age, and the findings of this study add to this concept.

There is no doubt that Southern Ocean processes must have played a critical role in these rapid climate shifts and the fossil corals provide the only possible way to examine Southern Ocean processes on these timescales.

Dr Tao Li, Study Lead Author, Nanjing University

In another study reported recently in the Nature Geoscience journal, the same research team rejected the latest predictions that the global rise in CO2 at the end of the ice age might have been associated with the discharge of geological carbon from deep-sea sediments.

According to Andrea Burke at St Andrew’s School of Earth and Environmental Sciences, “There have been some suggestions that reservoirs of carbon deep in marine mud might bubble up and add CO2 to the ocean and the atmosphere, but we found no evidence of this in our coral samples.”

Our robust reconstructions of radiocarbon at intermediate depths yields powerful constraints on mixing between the deep and upper ocean, which is important for modelling changes in circulation and carbon cycle during the last ice age termination.

Dr Tianyu Chen, Nanjing University

Although the rise in CO2 at the end of the ice age was dramatic in geological terms, the recent rise in CO2 due to human activity is much bigger and faster. What the climate system will do in response is pretty scary,” Dr James Rae added.

Journal Reference:

Li, T., et al. (2020) Rapid shifts in circulation and biogeochemistry of the Southern Ocean during deglacial carbon cycle events. Science Advances.

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