Around 56 million years ago, a large release of greenhouse gases, most likely generated by volcanic activity, resulted in intense global warming known as the Paleocene-Eocene Thermal Maximum (PETM).
According to research, the PETM was preceded by a smaller episode of warming and ocean acidification triggered by a shorter burst of carbon emissions.
Recent Studies
According to the latest results published in Science Advances on March 16, the quantity of carbon released into the atmosphere during this precursor event was nearly the same as current total carbon emissions from fossil fuel combustion and other human activities.
As a result, the short-lived precursor event indicates what may happen if current emissions are swiftly reduced. Still, PETM highlights the effects of continuing to emit carbon into the atmosphere at the current pace.
According to coauthor James Zachos, professor of Earth and planetary sciences, and Ida Benson Lynn Chair of Ocean Health at UC Santa Cruz, "It was a short-lived burp of carbon comparable to what they've already released from manmade emissions."
Because the deep-sea reservoir is so large, carbon would ultimately get mixed into the deep sea if they cut off emissions today, and its signal would vanish.
This process would take hundreds of years, which is a long period by human standards but a small time compared to the tens of thousands of years it took Earth's climate system to recover from the more intense PETM.
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Examining Marine Sediments
The new findings are based on examining marine sediments deposited in shallow seas off the coast of the United States. The Atlantic Coastal Plain presently encompasses the whole Atlantic coast. Sea levels were greater at the time of the PETM, and most of Maryland, Delaware, and New Jersey were under water.
In their investigation, the researchers used sediment cores excavated by the United States Geological Survey (USGS) from this location.
A huge shift in carbon isotope composition and other signs of severe changes in ocean chemistry due to the ocean absorbing massive volumes of carbon dioxide from the atmosphere mark the PETM in marine sediments.
The minuscule shells of small sea animals called foraminifera that lived in the ocean's surface waters can be found in marine sediments. The chemical makeup of these shells offers evidence of rising surface water temperatures and ocean acidification, and the environmental conditions in which they evolved.
Tali Babila, the study's first author, began working on it as a postdoctoral fellow with Zachos at UC Santa Cruz and is now at the University of Southampton in the United Kingdom. The researchers used novel analytical methods developed at Southampton to analyze the boron isotope composition of individual foraminifera to reconstruct a detailed record of ocean acidification.
This was part of geochemical investigations they used to piece together environmental changes between the precursor event and the major PETM.
Revealing Evidence
Sediments from the continental portion at Big Horn Basin in Wyoming and a few other sites have previously revealed evidence of a preceding warming episode. However, it was unclear if it constituted a worldwide signal because it was missing from deep-sea sediment cores.
This makes sense, according to Zachos, because oceanic sedimentation rates are sluggish, and the signal from a short-lived event would be lost owing to sediment mixing by bottom-dwelling marine life.
Along the Atlantic Coastal Plain, the USGS and others have drilled several sediment cores (or sections). The PETM is present in all of those portions, and some of them also catch the precursor event, according to the researchers. The latest analysis focuses on two Maryland parts (South Dover Bridge and Cambridge-Dover Airport).
Based on their findings, the researchers determined that the precursor signal in the Maryland parts was part of a worldwide event that lasted several centuries, if not millennia.
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