Northwestern-Led Teams Uncover Findings on Prehistoric Environmental Disruption

Two teams of geoscientists from Northwestern University have uncovered new findings on the chronology and character of events that led to an extreme environmental disruption that occurred nearly 100 million years ago. This event, known as the Ocean Anoxic Event 2 (OAE2), led to a choking of oxygen from the oceans and elevated marine extinction levels that affected the entire globe. The event was co-discovered more than 40 years ago by the late Seymour Schlanger, a professor at Northwestern.

The researchers studied preserved planktonic microfossils and bulk sediment extracted from three sites around the world and collected direct evidence indicating that ocean acidification occurred during the earliest stages of the event, due to carbon dioxide (CO2) emissions from the eruption of massive volcanic complexes on the sea floor. The findings, which were published in the journal Nature Geoscience, also propose a new hypothesis to explain why ocean acidification led to a strange blip of cooler temperatures, known as the “Plenus Cold Event,” which briefly interrupted the otherwise intensely hot greenhouse period.

A complementary paper detailing findings from ancient malformed microfossils was also published in the journal Communications Earth & Environment on December 13. The researchers hope that by analyzing how an influx of CO2 from volcanoes affected ocean chemistry, biomineralization and climate, they can better understand how today’s Earth is responding to an increase of CO2 due to human activities, which could potentially lead to solutions for adapting to and mitigating anticipated consequences.

“Ocean acidification and anoxia resulted from massive CO2 release from volcanoes,” said Northwestern’s Brad Sageman, a senior co-author of both studies. “These major CO2 emission events in Earth’s history provide the best examples we have of how the Earth system responds to very large inputs of CO2. This work has fundamental applicability to our understanding of the climate system, and our ability to predict what will happen in the future.”

“Based on isotopic analyses of the element calcium, we propose a possible explanation for the Plenus Cold Event, which is that a slowdown in biocalcification rates due to ocean acidification allowed alkalinity to accumulate in seawater,” said Northwestern’s Andrew Jacobson, a senior co-author of both studies. “Increased alkalinity led to a drawdown of CO2 from the atmosphere. It could very well be the case that such cooling is a predictable — but transitory — consequence of warming. Our results for OAE2 provide a geological analog for ocean alkalinity enhancement, which is a leading strategy for mitigating the anthropogenic climate crisis.”

Sageman and Jacobsen are both professor’s in Northwestern’s Department of Earth and Planetary Sciences. Learn more about their research in Northwestern Now’s article, “Malformed seashells, ancient sediment provide clues about Earth’s past.”