Effects of ancient carbon releases suggest possible scenarios for future climate

Date:
March 16, 2022
Source:
University of California - Santa Cruz
Summary:
A massive release of greenhouse gases, likely triggered by volcanic
activity, caused a period of extreme global warming known as the
Paleocene-Eocene Thermal Maximum (PETM) about 56 million years
ago. A new study now confirms that the PETM was preceded by a
smaller episode of warming and ocean acidification caused by a
shorter burst of carbon emissions. The short-lived precursor event
represents what might happen if current emissions can be shut down
quickly, while the much more extreme global warming of the PETM
shows the consequences of continuing to release carbon into the
atmosphere at the current rate.



FULL STORY ==========================================================================
A massive release of greenhouse gases, likely triggered by volcanic
activity, caused a period of extreme global warming known as the Paleocene-Eocene Thermal Maximum (PETM) about 56 million years ago. A
new study now confirms that the PETM was preceded by a smaller episode
of warming and ocean acidification caused by a shorter burst of carbon emissions.


==========================================================================
The new findings, published March 16 in Science Advances, indicate that
the amount of carbon released into the atmosphere during this precursor
event was about the same as the current cumulative carbon emissions from
the burning of fossil fuels and other human activities. As a result,
the short-lived precursor event represents what might happen if current emissions can be shut down quickly, while the much more extreme global
warming of the PETM shows the consequences of continuing to release
carbon into the atmosphere at the current rate.

"It was a short-lived burp of carbon equivalent to what we've already
released from anthropogenic emissions," said coauthor James Zachos,
professor of Earth and planetary sciences and Ida Benson Lynn Chair of
Ocean Health at UC Santa Cruz. "If we turned off emissions today, that
carbon would eventually get mixed into the deep sea and its signal would disappear, because the deep-sea reservoir is so huge." This process
would take hundreds of years -- a long time by human standards, but
short compared to the tens of thousands of years it took for Earth's
climate system to recover from the more extreme PETM.

The new findings are based on an analysis of marine sediments that were deposited in shallow waters along the U.S. Atlantic coast and are now
part of the Atlantic Coastal Plain. At the time of the PETM, sea levels
were higher, and much of Maryland, Delaware, and New Jersey were under
water. The U.S.

Geological Survey (USGS) has drilled sediment cores from this region
which the researchers used for the study.

The PETM is marked in marine sediments by a major shift in carbon isotope composition and other evidence of dramatic changes in ocean chemistry
as a result of the ocean absorbing large amounts of carbon dioxide from
the atmosphere. The marine sediments contain the microscopic shells of
tiny sea creatures called foraminifera that lived in the surface waters
of the ocean.

The chemical composition of these shells records the environmental
conditions in which they formed and reveals evidence of warmer surface
water temperatures and ocean acidification.



========================================================================== First author Tali Babila began the study as a postdoctoral fellow working
with Zachos at UC Santa Cruz and is now at the University of Southampton,
U.K. Novel analytical methods developed at Southampton enabled the
researchers to analyze the boron isotope composition of individual
foraminifera to reconstruct a detailed record of ocean acidification. This
was part of a suite of geochemical analyses they used to reconstruct environmental changes during the precursor event and the main PETM.

"Previously, thousands of foraminifera fossil shells were needed for
boron isotope measurement. Now we are able to analyze a single shell
that's only the size of a grain of sand," Babila said.

Evidence of a precursor warming event had been identified previously
in sediments from the continental section at Big Horn Basin in Wyoming
and a few other sites. Whether it was a global signal remained unclear, however, as it was absent from deep-sea sediment cores. Zachos said
this makes sense because sedimentation rates in the deep ocean are slow,
and the signal from a short- lived event would be lost due to mixing of sediments by bottom-dwelling marine life.

"The best hope for seeing the signal would be in shallow marine basins
where sedimentation rates are higher," he said. "The problem there is that deposition is episodic and erosion is more likely. So there's not a high likelihood of capturing it." The USGS and others have drilled numerous sediment cores (or sections) along the Atlantic Coastal Plain. The
researchers found that the PETM is present in all of those sections,
and several also capture the precursor event. Two sections from Maryland
(at South Dover Bridge and Cambridge-Dover Airport) are the focus of
the new study.



========================================================================== "Here we have the full signal, and a couple of other locations capture
part of it. We believe it's the same event they found in the Bighorn
Basin," Zachos said.

Based on their analyses, the team concluded that the precursor signal
in the Maryland sections represents a global event that probably lasted
for a few centuries, or possibly several millennia at most.

The two carbon pulses -- the short-lived precursor and the much larger and
more prolonged carbon emissions that drove the PETM -- led to profoundly different mechanisms and time scales for the recovery of the Earth's
carbon cycle and climate system. The carbon absorbed by the surface
waters during the precursor event got mixed into the deep ocean within
a thousand years or so. The carbon emissions during the PETM, however,
exceeded the buffering capacity of the ocean, and removal of the excess
carbon depended on much slower processes such as the weathering of
silicate rocks over tens of thousands of years.

Zachos noted that there are important differences between Earth's climate system today and during the Paleocene -- notably the presence of polar
ice sheets today, which increase the sensitivity of the climate to
greenhouse warming.

In addition to Babila and Zachos, the coauthors of the paper include
Gavin Foster and Christopher Standish at University of Southampton;
Donald Penman at Utah State University; Monika Doubrawa, Robert Speijer,
and Peter Stassen at KU Leuven, Belgium; Timothy Bralower at Pennsylvania
State University; and Marci Robinson and Jean Self-Trail at the USGS. This
work was funded in part by the National Science Foundation.


========================================================================== Story Source: Materials provided by
University_of_California_-_Santa_Cruz. Original written by Tim
Stephens. Note: Content may be edited for style and length.


========================================================================== Related Multimedia:
* Microscopic_shells_of_organisms_called_foraminifera ========================================================================== Journal Reference:
1. Tali L. Babila, Donald E. Penman, Christopher D. Standish, Monika
Doubrawa, Timothy J. Bralower, Marci M. Robinson, Jean
M. Self-Trail, Robert P. Speijer, Peter Stassen, Gavin L. Foster,
James C. Zachos.

Surface ocean warming and acidification driven by rapid carbon
release precedes Paleocene-Eocene Thermal Maximum. Science Advances,
2022; 8 (11) DOI: 10.1126/sciadv.abg1025 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/03/220316145749.htm

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