Unraveling 66 million years of climate history from ocean sediments

An international team of researchers has created a new climate reference curve by reconstructing the Earth’s climate since the end of the Cretaceous period using data obtained from sediment cores from the ocean floor.

The team of global experts, including Professor Paul Wilson from the University of Southampton, have compiled and analysed a comprehensive data set from deep sea sediment cores to produce a sort of ‘barcode-in-colour’ that shows how Earth’s climate and its carbon cycle have changed since the demise of the dinosaurs, 66 million years ago. Their findings are published in Science (https://science.sciencemag.org/cgi/doi/10.1126/science.aba6853).

The record of past climate and carbon cycle changes was dated by matching the pattern of high frequency changes in the sediments to rhythmic changes in Earth’s solar orbit calculated by astronomers. Like a metronome, these orbit fluctuations have dictated the cyclic patterns of climate change. By identifying these astronomical cycles in the data, 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 data set will serve as a basis for researchers worldwide to accurately correlate their results within the context of climate history. The authors emphasise that this is fundamental for testing the reliability of climate models for the future.

“Our mathematical analyses revealed what is at first invisible in the sediment - the hidden relationships and recurring patterns in the climate,” says co-leader of the team behind the research, Dr Norbert Marwan of Potsdam Institute for Climate Impact in Germany. “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.”

Layers of sediment on the ocean floor have been cored 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 microscopic fossils within, scientists are able to reconstruct and analyse global climate changes into the distant past.

The team examined the evidence preserved in oxygen and carbon isotopes, which provides information about the past deep-sea temperatures, global ice volume and the carbon cycle. These clues are stored in the shells of microorganisms that once lived on the sea floor and represent an archive of past climate conditions that researchers use to draw comparisons between the past, present and future.

“One lesson learned from our data is that Earth’s climate underwent some remarkable changes in response to relatively slow natural changes. That realisation is rather sobering when we consider how much faster humans are changing our atmosphere today than any of the natural changes that occurred at any time in the past 66 million years,” said Professor Wilson, Head of Southampton’s Palaeoceanography and Palaeoclimate Research Group.

Innovations in drilling strategy and technology in the early 90’s helped over the past few decades to recover the high-quality sediment archives required to produce a detailed global climate dataset. By applying advanced statistical methods, the team has developed a better understanding the climate conditions and dynamics of the past.

“Our record shows how Earth’s climate has undergone huge changes in baseline conditions from an ancient greenhouse world with lush forests on Antarctica and Greenland to the one that is more familiar to us today with large ice caps at the poles. The changes between these two climate states occurs at about half time (34 million years ago). And when we look closely at the pattern of short-term variability that is superimposed on the overall trend we see that Earth’s climate is a much more unpredictable beast with polar ice caps than without,” Professor Wilson continued. ”

Dr Thomas Westerhold from MARUM – Center for Marine Environmental Sciences at the University of Bremen and co-lead for the project, added: “We want to understand what climate conditions existed in the past, what processes lay behind them, and how they proceeded. The time from 66 to 34 million years ago, when the planet was significantly warmer than it is today, is especially interesting.”

Participating institutions involved in the research include: MARUM –University of Bremen (Germany); Potsdam Institute for Climate Impact Research (PIK, Germany); University of Potsdam, Institute of Geosciences (Germany); University College London (UK); Università degli Studi di Padova (Italy); GEOMAR Helmholtz-Zentrum für Ozeanforschung Kiel (Germany); University of Exeter (UK); University of St Andrews (UK); University of Southampton (UK); Istituto Nazionale di Geofisica & Vulcanologia, Rome (Italy); Institute for Climate Change Solutions, Pesaro e Urbino (Italy); University of Bremen (Germany); University of Cambridge (UK); Christian-Albrechts-University Kiel (Germany); University of Edinburgh (UK); University of Bristol (UK); Utrecht University (Netherlands); Oregon State University (USA); Tongji University, Shanghai (China); University of Hawaii (USA) and the University of California Santa Cruz (USA).