To determine ancient ocean temperatures, a multi-institutional team of scientists analyzed three long sediment columns cored from the seafloor off Suriname, in northeast South America. The black box marks their research location. (Illustration courtesy of the Ocean Drilling Program)
In a ship laboratory, WHOI paleoclimatologist Karen Bice studies data collected from freshly extracted sediment cores during the 2003 expedition. (Photo by Richard D. Norris, Scripps Institution of Oceanography)
Researchers gathered sediment cores in 2003 from the international Ocean Drilling Program’s drillship JOIDES Resolution. The vessel is named for the HMS Resolution, commanded by Captain James Cook more than 200 years ago. Like its namesake, the current vessel also sails for scientific exploration. (Photo courtesy of the Ocean Drilling Program)
The sediments Karen Bice studied to determine temperature changes contained both carbon-rich organic matter and the fossilized shells of microscopic marine organisms, such as those shown here. The organisms had settled and piled up on the seafloor over tens of millions of years. (Photo by Richard D. Norris, Scripps Institution of Oceanography (formerly of WHOI))
Scientists have found evidence that tropical Atlantic Ocean
temperatures may have once reached 107°F (42°C)—about 25°F (14°C)
higher than today. The surprisingly high ocean temperatures occurred
millions of years ago when carbon dioxide levels in Earth’s atmosphere
were high, the scientists said.
The findings, if confirmed, indicate that future ocean warming from the
buildup of heat-trapping carbon dioxide may be much greater than
predicted by computer models now used by scientists and policymakers to
forecast climate change.
“These temperatures are off the charts from what we’ve seen before,”
Karen Bice, a paleoclimatologist at Woods Hole Oceanographic
Institution, reported Feb. 17 at the annual meeting of the American
Association for the Advancement of Science. She was also lead author of
a study to be published this spring in the journal Paleoceanography.
“If the models are not right, society is not well informed or well
served.”
Warmer ocean temperatures cause more evaporation, which could shift
where and how much precipitation falls and could generate more intense
hurricanes and winter storms, Bice said.
High carbon dioxide levels To determine ancient ocean temperatures, a multi-institutional team of
scientists analyzed three long sediment columns cored from the seafloor
off Suriname, in northeast South America, by the international Ocean
Drilling Program’s drillship JOIDES Resolution.
The sediments contained both carbon-rich organic matter and the
fossilized shells of microscopic marine organisms that had settled and
piled up on the seafloor over tens of millions of years.
The scientists analyzed the shells’ chemistry, which changes along with
temperature changes in the surface waters where they lived. They
determined that ocean temperatures in the region ranged between 91° and
107°F (33° and 42°C) between 84 million and 100 million years ago, in
an era when dinosaurs roamed the Earth. In the same region now,
temperatures range between 75° and 82°F (24° and 28°C).
For the first time, scientists used the same sample to estimate ocean
temperatures and atmospheric CO2 levels, and thereby precisely
correlated both phenomena. Analyses of organic matter from the
sediments revealed that CO2 levels during the same time span were 1,300
to 2,300 parts per million (ppm), compared with 380 ppm today.
How reliable are current climate forecast models? The findings question the reliability of well-accepted models that
simulate global climate. When 1,300 to 2,300 ppm of carbon dioxide is
factored into the models, they do not produce such high ocean
temperatures.
“The climate models underestimate temperatures and the amount of
warming that would accompany a CO2 increase more than 1000 ppm above
today’s level,” Bice said.”
Current models may be missing a critical factor that amplifies heating,
Bice said. During past warm periods, oceans and wetlands may have
released large amounts of methane gas to the atmosphere. Methane traps
heat 10 times more effectively than carbon dioxide.
But even when extraordinarily high concentrations of methane are
factored into current models, they still fail to reproduce ocean
temperatures as high as 107°F. That suggests that the models may
underestimate the climate system’s response to increased greenhouse
gases.
“This study addresses how the ocean-climate system changed in the past,
long before people had any impacts,” said paleoceanographer Mark Leckie
of the University of Massachusetts, Amherst, who reviewed the study for
Paleooceanography. “I think Karen’s research should be another wake-up
call to the rate at which we are changing the system today.”
The research was funded by the WHOI Ocean and Climate Change Institute and a WHOI independent study award. Funding
was also provided by the U.S. Science Support Program of Joint
Oceanographic Institutions, The Andrew W. Mellon Foundation Endowed
Fund for Innovative Research, and Deutsche Forschungsgemeinschaft
through Research Center Ocean Margins.
