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Night vision of the scientific drillship JOIDES Resolution that recovered multimillion year past climate archives for the bottom of the world oceans. Photo: Adam Kurtz

Scientists unravel 66 million years of climate history from ocean sediments

Pioneering new analysis of deep-sea sediments has revealed the climatic changes over the last 66 million years of Earth’s history - which can be studied like a ‘colorful barcode’.

An international team of researchers, including Dr Kate Littler at the University of Exeter, has examined data from sediment cores from the ocean floor, in order to reconstruct Earth’s climate at unprecedented temporal resolution.

For the new analysis the team, led by Dr. Thomas Westerhold of MARUM from the Center for Marine Environmental Sciences at the University of Bremen and Dr. Norbert Marwan of the Potsdam Institute for Climate Impact Research (PIK), compiled and analyzed a comprehensive dataset obtained from sediment cores from beneath the ocean floor.

Innovative statistical methods for studying complex dynamical systems were applied revealing fundamental climate states, showing the deterministic nature of climate changes over very long periods of time.

The research is published in leading journal, Science.

Dr Littler, a Senior Lecturer at the University of Exeter and co-author said: “This new composite climate and carbon-cycle record is the result of literally thousands of hours of people-power, analyzing thousands of samples, across multiple institutes and countries, over the past 30 years. The Cenozoic isotope splice will be one of the lasting legacies of scientific ocean drilling”.

Layers of sediment on the ocean floor have been cored by the drill ship JOIDES Resolution across the world for more than five decades through internationally coordinated scientific ocean drilling expeditions of the International Ocean Discovery Program (IODP) and its predecessor programs (DSDP, ODP, IODP).

By studying these sediments and the microfossils within, scientists are able to reconstruct and analyze global climate changes into the distant past. They examine the evidence preserved in oxygen and carbon isotopes, which provides information about the past deep-sea temperatures, global ice volumes and the carbon cycle.

These clues are stored in the shells of microorganisms that once lived on the sea floor. They represent an archive of past climate conditions that researchers use to draw comparisons between the past, present and future.

The framework of a global climate reference curve has existed since 2001, although the data coverage older than 34 million years was generally poor.

Since that pioneering work, however, the climate records obtained from many new sediment cores have improved, both quantitatively and qualitatively. Particularly over the past two decades, scientific drilling programs have targeted their drilling into older geological strata. Researchers therefore now have access to higher quality, more complete sediment archives, and are able to reconstruct global climate in much more detail than ever before.

The new climate reference curve, called CENOGRID (CENOzoic Global Reference benthic foraminifer carbon and oxygen Isotope Dataset), is a reconstruction of the Earth’s climate since the last great extinction 66 million years ago, which introduced a new Era, the Cenozoic.

“Our goal was to create a new reference of past climate over the last 66 million years, which not only incorporates the highest-resolution data but is also more accurately dated,” explains first author Thomas Westerhold. “We now know more accurately when it was warmer or colder on the planet and we also have a better understanding of the underlying dynamics.”

“Our mathematical analyses revealed what is at first invisible in the sediment - the hidden relationships and recurring patterns in the climate,” says Norbert Marwan of PIK. “So the view into the past is also a glimpse into the future. We can learn something about the staggeringly rapid anthropogenic changes of our present century from the slow natural climate fluctuations occurring over millions of years.”

The age model is the key component of the new reference curve. Recurring patterns in the sediment cores, called Milanković cycles, reflect changes in the Earth’s orbit around the sun. Like a metronome, these fluctuations have dictated the cyclic patterns of climate change.

By identifying these astronomical cycles, the climate of the past 66 million years has now been timed continuously for the first time, allowing it to be dated much more accurately than ever before.

In the future, the new climate reference curve CENOGRID can serve as a basis for researchers worldwide to accurately correlate their data within the context of climate history. With more data, it is now possible to not only further refine the picture of the climatic past, but also to identify regional intricacies. The authors emphasize that this is fundamental for testing the reliability of climate models for the future.

Dr Littler added: “In addition to telling us important information about Earth’s past, the CENOGRID also shines a light on Earth’s near future. Importantly, the new record demonstrates that the magnitude of predicted warming by 2300 under business as usual will far exceed the natural periodic variability over the last 66 million years. We are heading for uncharted waters”.

Date: 10 September 2020

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