Ancient climate shift sheds light on future global warming

According to widely accepted models, a dramatic cooling event and significant drop in sea levels roughly 34 million years ago, during the Eocene-Oligocene transition, should have resulted in widespread erosion across the continents. This would have deposited vast amounts of sandy material onto the ocean floor. 

The Eocene-Oligocene transition marked one of the most extreme climate shifts since the extinction of the dinosaurs, transforming Earth’s climate from a “greenhouse” into an “icehouse” one. 

Yet, a new review from Stanford University reveals a surprising contradiction: across the margins of all seven continents, there is little to no sediment from this period to be found.

Climate clues in the geologic record 

This unexpected finding, published in Earth-Science Reviews, uncovers a puzzling global gap in the geologic record. 

“The results have left us wondering, ‘where did all the sediment go?’” said senior author Stephan Graham, a professor in the Stanford Doerr School of Sustainability. 

“Answering that question will help us get a better fundamental understanding about the functioning of sedimentary systems and how climatic changes imprint on the deep marine sedimentary record.”

Environmental effects of climate shifts

The discovery challenges existing models of sediment deposition and erosion and offers new insights into the global environmental effects of significant climate shifts. 

The findings may also provide a clearer understanding of how today’s rapid climate change might reshape Earth’s surface.

“For the first time, we’ve taken a global look at an understudied response of the planet’s largest sediment mass-movement systems during the extreme transition of the Eocene-Oligocene,” explained lead author Zack Burton, now an assistant professor of Earth sciences at Montana State University. 

The Eocene-Oligocene transition was a period of profound planetary cooling. Large ice sheets formed in Antarctica, which had previously been ice-free, global sea levels fell sharply, and there were significant die-offs among both marine and terrestrial species. 

Before this period, Earth had experienced some of the highest temperatures and sea levels since the age of the dinosaurs, according to climate proxy records. Burton and his colleagues initially set out to investigate the effects of these early Eocene warm conditions on deep-sea depositional systems. 

Detailed analysis of the climate shift

In a 2023 study published in Nature Scientific Reports, they found evidence of abundant sand-rich deposits along Earth’s continental margins, which they attributed to intensified weather conditions that increased erosion from land. 

The team then decided to extend their study to cover the later Eocene and early Oligocene, during which Earth rapidly cooled and entered an “icehouse” climate.

To do this, the researchers conducted a meticulous review of hundreds of scientific papers spanning over a century. They analyzed studies that documented ancient sediment, often buried several kilometers beneath the ocean floor. 

This comprehensive review included findings from offshore oil and gas drilling, onshore rock outcrops, and seismic data interpretations. Altogether, the study examined over 100 geographical sites worldwide, providing a detailed look at the geologic records from the margins of all continents.

As the team combed through the collected data, they found a baffling absence of sand-rich sediments from the Eocene-Oligocene transition. 

Missing sediments in the geologic record 

“We didn’t see abundant sand-rich deposition, as in our study of warm climates of the early Eocene,” Burton said. 

“Instead, we saw that prominent, widespread erosional unconformities – in other words, gaps in the rock record – had developed during the extreme climatic cooling and oceanographic change of the Eocene-Oligocene.”

The researchers propose several theories to explain the missing sediments. One idea is that strong ocean bottom currents, driven by changes in temperature and salinity triggered by the climate shift, could have scoured the ocean floor, eroding sediments that flowed off the continents. 

Another possibility is that the rapid drop in sea levels exposed continental shelves, allowing sediments to bypass nearer sedimentary basins and be deposited much farther out on the ocean’s abyssal plains. Additionally, glacial erosion around Antarctica may have played a role in redistributing sediments.

Profound changes across land and sea

These processes appear to have operated across the globe, suggesting that the sedimentary record was influenced by global climatic controls. The researchers believe that this global impact points to the profound climatic changes felt not only on land but also in the deepest oceanic basins.

The study’s findings provide a valuable perspective on how Earth’s surface can respond to significant climate shifts. 

The Eocene-Oligocene transition offers a window into the large-scale environmental transformations that can result from rapid climate change, something that is highly relevant to understanding today’s human-driven climate shifts.

Radical changes with rapid climate change 

Although the current climate change crisis is smaller in overall magnitude compared to the Eocene-Oligocene transition, it is unfolding at a much faster pace. 

The researchers believe that studying these past events can help scientists better predict the kinds of drastic changes that may occur as Earth’s climate continues to change rapidly.

“Our findings can help inform us of the kinds of radical changes that can happen on the Earth’s surface in the face of rapid climate change,” Graham said. “The geologic past informs the present, and particularly the future.”

By reexamining past climatic events and sedimentary responses, scientists hope to gain insights that could guide our understanding of the challenges posed by modern climate change, and potentially help mitigate its effects on Earth’s ecosystems and surface environments.

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