Ancient climate analysis reveals unknown global processes

According to the highly cited traditional model, cooling and a significant drop in sea level around 34 million years ago should have led to widespread continental erosion, depositing vast amounts of sandy material on the ocean floor. After all, this was one of the most drastic climate changes on Earth since the extinction of the dinosaurs.

But a new Stanford University review of hundreds of studies dating back several decades finds that, by contrast, little or no deposits dating back to this transition period have been found across the margins of all seven continents. It is reported that there is no The discovery of this widespread global gap in the geological record was published this week in Earth-Science Reviews.

“This result leaves us with the question, ‘Where did all the sediment go?'” said the study’s lead authors Welton Joseph and Maud Lanphear of the Stanford Doerr School of Sustainability. – Crook Professor Stephen Graham said. “Answering that question will help us gain a better fundamental understanding of how sedimentary systems function and how climate change will affect the deep-sea sedimentary record.”

The geological gap provides new insights into the processes of sediment deposition and erosion, as well as broader environmental signals from dramatic climate change, allowing researchers to understand the global magnitude of today’s climate change. It may help us better understand the situation.

“For the first time, we examine on a global scale the understudied response of Earth’s largest sedimentary mass transport system during the extreme Eocene-Oligocene transition,” said study lead author Zach Burton. said the doctor. ’20, and is currently an assistant professor of geosciences at Montana State University.

Tim McHargue, adjunct professor of Earth and Planetary Sciences at Stanford University, is also a co-author of the study.

From the greenhouse to the icehouse

From the Eocene to the Oligocene, Earth underwent severe planetary cooling. A huge ice sheet appeared on the previously ice-free Antarctic continent, lowering global sea levels and causing severe extinction of land and marine life.

Previously, during the early Eocene epoch, which lasted from about 56 million years ago to 34 million years ago, global temperatures were the lowest since dinosaurs walked the earth more than 66 million years ago, according to climate proxy records. It was warm and the sea level was at its highest. .

Burton and colleagues initially focused on investigating the effects of early Eocene conditions on deep-sea sedimentary systems. The results, published in Scientific Reports in 2023, found that ocean basins along Earth’s continental margins are rich in sand-rich sediments.

The research team attributed this increase in sedimentation primarily to intensifying climate and weather conditions, which accelerated erosion from land. Their curiosity piqued, Burton and his colleagues investigated the late Eocene and early Oligocene periods, when the Earth suddenly changed from a “greenhouse” and “hothouse” climate to its opposite, an “icehouse” climate. Expanded.

For the new study, the researchers combed through the scientific and technical literature that records ancient sediments up to several kilometers below the ocean floor, examining studies published from the past decade to more than a century ago. The literature includes offshore oil and gas drilling studies, onshore rock outcrop studies, and even the interpretation of seismic data to infer the characteristics of Eocene to Oligocene sediments. In total, it includes more than 100 geographic sites from around the world, providing an overview of every land mass on the continent.

Although the study’s literature analysis techniques are not new, Graham said the scale of such an approach, made possible by vast online databases, could prove highly thought-provoking. Ta. “There may be other similar events in the geological past that require more detailed investigation,” Graham said. “And the way to start that is to do exactly what we did: comb through the world’s geological literature for a particular questionable period.” ”

“The actual process of reevaluating, reexamining, and reanalyzing literature that has been published, in some cases for decades, is difficult but can be very rewarding,” Burton said. “This method can lead to exciting and unexpected discoveries, as we have here.”

completely unexpected

As Barton and his colleagues looked through the compiled data inventory, they became increasingly perplexed by the apparent absenteeism.

“We didn’t see rich, sand-rich deposits like we did when we studied warmer climates in the early Eocene,” Burton said. “Instead, we found that a significant and widespread erosional unconformity, or in other words, a gap in the rock record, occurred during the Eocene-Oligocene extreme climate cooling and changes in ocean structure.”

Researchers have proposed several theories as to why this lack of deposition occurred. Intense submarine currents, driven by water temperature and salinity, may have been triggered or amplified by large-scale climate change, eroding the ocean floor and displacing sediments washed away from continents.

On the other hand, mechanisms from continental shelves exposed by lower sea levels may have driven sediments to far-flung abyssal plains, completely bypassing closer sedimentary basins. More regionally localized processes, such as glacial erosion around Antarctica, are also likely to have had an impact.

Whatever mechanisms were at work, they collectively created a similar landscape of erosion in ocean basins on every continent. This ubiquity indicates what the researchers called global control, meaning that severe climate change was felt everywhere from the highest landmasses to the deepest bodies of water.

In this way, the sudden climate event at the Eocene-Oligocene boundary and its newly observed significant effects along continental margins are the key to the global climate change that researchers are currently experiencing. It may help us better understand the enormity. Human-induced climate change over the past few centuries is now occurring at an alarmingly rapid pace, although the overall magnitude is much smaller than during the Eocene-Oligocene transition, Stanford University researchers say. said.

“Our findings help inform what rapid changes may occur on Earth’s surface in the face of rapid climate change,” Graham said. “The geological past informs the present and especially the future.”