How fossil corals can shed light on the Earth's past climate

Staghorn coral (Acropora cervicornis). Credit: Wikipedia

In a paper published today in Science, researchers from the University of Bristol describe how they used radiocarbon measured in deep-sea fossil corals to shed light on carbon dioxide (CO2) levels during the Earth's last deglaciation.

Around 18,000-11,000 years ago, the Earth's climate system experienced a dramatic shift: a period known to paleoclimate scientists as the last deglaciation. During this period, atmospheric CO2 concentration increased by ~80 parts per million (ppm), accompanied by sea level rise of almost 120 metres due to ice sheet melting and global warming.

Recent high-resolution ice core CO2 records have revealed that there were three abrupt centennial-scale atmospheric CO2 increases of ~10 ppm superimposed on the more gradual millennial-scale deglacial CO2 rise. The second and third of these events also coincided with abrupt warming of the high latitude North Atlantic region.

The rate of Atlantic Meridional Overturning Circulation - that is, the formation in the high latitudes and associated upwelling - is closely related to the temperature of the North Atlantic region and thus might also be related to these CO2 releasing events. However it has been remarkably hard to find marine archives that can show how deep oceans behave on rapid timescales.

Researchers from the University of Bristol, University of St Andrews and University of California Irvine tackled this problem using radiocarbon measured in deep-sea fossil corals. The corals were recovered by scientific research expeditions to the Equatorial Atlantic and Southern Ocean, funded by the European Research Council and the US National Science Foundation.

Fossil corals have the unique advantage that they can be precisely dated by radiometric uranium-series dating, giving an age scale that can be directly compared to the ice core records. Radiocarbon is introduced into the ocean at the surface and penetrates to deeper layers through deep water formation. During this process radiocarbon decays away, so that deep-sea radiocarbon - and, therefore, the reconstructed fossil coral radiocarbon - can provide information on the past strength of deep ocean circulation.

The measurements revealed two massive transient events where the water becomes homogenized and enriched in radiocarbon in the mid-depth equatorial Atlantic and the Drake Passage, in phase with the second two abrupt increases of the atmosphere CO2 concentration during the last deglaciation.

Lead author, Dr Tianyu Chen of Bristol's School of Earth Sciences said: "Our data are consistent with two transient and enhanced deep Atlantic overturning events which flushed out respired carbon in the deep water, causing a rapid rise of atmosphere CO2 concentration and abrupt warming of the high latitude North Atlantic."

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More information: 'Synchronous Centennial Abrupt Events in the Ocean and Atmosphere during the Last Deglaciation' by Tianyu Chen, Laura F. Robinson, Andrea Burke, John Southon, Peter Spooner, Paul J. Morris and Hong Chin Ng in Science: … 1126/science.aac6159
Journal information: Science

Citation: How fossil corals can shed light on the Earth's past climate (2015, September 24) retrieved 19 July 2019 from
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User comments

Sep 24, 2015
This sounds like a cool way to understand our past, and relate it to what is happening today. We need all of the baselines we can get to understand if what is happening today is abnormal or not; on geologic timescales.

One thing that I don't get. How could C02 levels gone up...humanity was not putting it into the air - were they?

Sep 25, 2015
I wonder what those people were driving and what industries were contributing to THAT increase in Man Made Global Warming? A denier, I know.
You see, I am a skeptic of all research with a political agenda. "Statistics never but liars use statistics".

Sep 25, 2015
The carbon 14 decay in deep ocean deposits as well as carbon 14 in diamonds is entirely consistent with nuclear fission at the core of the planet; per published works of J. Marvin Herndon, Robert J. Tuttle, Tom van Flandern, and many others. Not fusion, not radioactive decay. Fission, due to the accretion of uranium hydride to the core of every planet and major moon, as well as stars. Herndon's GeoReactor is the true cause of global warming AND the uptick in CO2. Stars are big H-bombs (fission causing fusion). Dr. Padmanabha Rao published in the July - August, 2013 edition of Journal of Applied Physics about his observation of the signature daughter elements of U-235 in solar flares, and likewise deduced fission at the core of the Sun.

Sep 28, 2015
denglish says: "One thing that I don't get. How could C02 levels gone up...humanity was not putting it into the air - were they?"

For denglish: "The primary natural source of carbon-14 on Earth is cosmic ray action on nitrogen in the atmosphere, and it is therefore a cosmogenic nuclide. However, open-air nuclear testing between 1955–1980 contributed to this pool." (wikipedia)

In other words, Carbon 14 is made at a more or less constant rate from nitrogen by a nuclear reaction induced by cosmic rays. Then, over a half life, the carbon decays. When an organism dies, its carbon 14 clock begins.

But there are many clocks that operate over much longer time scales, eg - uranium mentioned in the article.

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