A series of global
warming events called hyperthermals that occurred more than 50 million years
ago had a similar origin to a much larger hyperthermal of the period, the
Pelaeocene-Eocene Thermal Maximum (PETM), new research has found. The findings,
published online in Nature Geoscience,
represent a breakthrough in understanding the major “burp” of carbon,
equivalent to burning the entire reservoir of fossil fuels on Earth, that
occurred during the PETM.
“As geologists, it
unnerves us that we don’t know where this huge amount of carbon released in the
PETM comes from,” says Will Clyde, associate professor of Earth sciences at the
University of New Hampshire and a co-author on the
paper. “This is the first breakthrough we’ve had in a long time. It gives us a
new understanding of the PETM.” The work confirms that the PETM was not a
unique event—the result, perhaps, of a meteorite strike—but a natural part of
the Earth’s carbon cycle.
Working in the Bighorn Basin
region of Wyoming, a 100-mile-wide area with a
semi-arid climate and stratified rocks that make it ideal for studying the
PETM, Clyde and lead author Hemmo Abels of Utrecht
University in the Netherlands
found the first evidence of the smaller hyperthermal events on land.
Previously, the only evidence of such events were from marine records.
“By finding these smaller
hyperthermal events in continental records, it secures their status as global
events, not just an ocean process. It means they are atmospheric events,” Clyde says.
Their findings confirm
that, like the smaller hyperthermals of the era that released carbon into the
atmosphere, the release of carbon in the PETM had a similar origin. In
addition, the warming-to-carbon release of the PETM and the other hyperthermals
are similarly scaled, which the authors interpret as an indication of a similar
mechanism of carbon release during all hyperthermals, including the PETM.
“It points toward the
fact that we’re dealing with the same source of carbon,” Clyde
Working in two areas of
the Bighorn Basin
just east of Yellowstone National Park—Gilmore Hill and Upper Deer Creek—Clyde and Abels sampled rock and soil to measure carbon
isotope records. They then compared these continental recordings of carbon
release to equivalent marine records already in existence.
During the PETM,
temperatures rose between 5 C and 7 C in approximately 10,000 years—”a
geological instant,” Clyde calls it. This rise
in temperature coincided exactly with a massive global change in mammals, as
land bridges opened up connecting the continents. Prior to the PETM, North America had no primates, ancient horses, or
split-hoofed mammals like deer or cows.
Scientists look to the
PETM for clues about the current warming of the Earth, although Clyde cautions that “the Earth 50 million years ago was
very different than it is today, so it’s not a perfect analog.” While
scientists still don’t fully understand the causes of these hyperthermal
events, “they seem to be triggered by warming,” Clyde
says. It’s possible, he says, that less dramatic warming events destabilized
these large amounts of carbon, releasing them into the atmosphere where they,
in turn, warmed the Earth even more.
“This work indicates that there is some part of the
carbon cycle that we don’t understand, and it could accentuate global warming,”