Drilling platform resting on the ice cover of Lake E; the container in front holds generators. Credit: Olaf Juschus |
Intense
warm climate intervals—warmer than scientists thought possible—have
occurred in the Arctic over the past 2.8 million years.
That
result comes from the first analyses of the longest sediment cores ever
retrieved on land. They were obtained from beneath remote, ice-covered
Lake El’gygytgyn (pronounced El’gee-git-gin) (“Lake E”) in the
northeastern Russian Arctic.
The journal Science published the findings this week.
They
show that the extreme warm periods in the Arctic correspond closely
with times when parts of Antarctica were also ice-free and warm,
suggesting a strong connection between Northern and Southern Hemisphere
climate.
The
polar regions are much more vulnerable to climate change than
researchers thought, say the National Science Foundation-(NSF) funded
Lake E project’s co-chief scientists: Martin Melles of the University of
Cologne, Germany; Julie Brigham-Grette of the University of
Massachusetts Amherst; and Pavel Minyuk of Russia’s North-East
Interdisciplinary Scientific Research Institute in Magadan.
The
exceptional climate warming in the Arctic, and the inter-hemispheric
interdependencies, weren’t known before the Lake E studies, the
scientists say.
Lake
E was formed 3.6 million years ago when a huge meteorite hit Earth,
leaving an 11-mile-wide crater. It’s been collecting layers of sediment
ever since.
The
lake is of interest to scientists because it has never been covered by
glaciers. That has allowed the uninterrupted build-up of sediment at the
bottom of the lake, recording hitherto undiscovered information on
climate change.
Cores from Lake E go far back in time, almost 30 times farther than Greenland ice cores covering the past 110,000 years.
The
sediment cores from Lake El’gygytgyn reflect the climate and
environmental history of the Arctic with great sensitivity, say
Brigham-Grette and colleagues.
Location of Lake E 100 kilometers north of the Arctic Circle in northeastern Russia. Credit: Arctic Climate Impact Assessment |
The
physical, chemical and biological properties of Lake E’s sediments
match the known global glacial/interglacial pattern of the ice ages.
Some
warm phases are exceptional, however, marked by extraordinarily high
biological activity in the lake, well above that of “regular” climate
cycles.
To
quantify the climate differences, the scientists studied four warm
phases in detail: the two youngest, called “normal” interglacials, from
12,000 years and 125,000 years ago; and two older phases, called “super”
interglacials, from 400,000 and 1.1 million years ago.
According
to climate reconstructions based on pollen found in sediment cores,
summer temperatures and annual precipitation during the super
interglacials were about 4 to 5 degrees C warmer, and about 12 inches
wetter, than during normal interglacials.
The
super interglacial climates suggest that it’s nearly impossible for
Greenland’s ice sheet to have existed in its present form at those
times.
Simulations
using a state-of-the-art climate model show that the high temperature
and precipitation during the super interglacials can’t be explained by
Earth’s orbital parameters or variations in atmospheric greenhouse gases
alone, which geologists usually see as driving the glacial/interglacial
pattern during ice ages.
That suggests that additional climate feedbacks are at work.
“Improving
climate models means that they will better match the data that has been
collected,” says Paul Filmer, program director in NSF’s Division of
Earth Sciences, which funded the “Lake E” project along with NSF’s
Office of Polar Programs.
“The
results of this collaboration among scientists in the U.S., Austria,
Germany and Russia are providing a challenge for researchers working on
climate models: they now need to match results from Antarctica,
Greenland—and Lake El’gygytgyn.”
Adds
Simon Stephenson, director of the Division of Arctic Sciences in NSF’s
Office of Polar Programs, “This is a significant result from NSF’s
investment in frontier research during the recent International Polar
Year.
“‘Lake
E’ has been a successful partnership in very challenging conditions.
These results make a significant contribution to our understanding of
how Earth’s climate system works, and improve our understanding of what
future climate might be like.”
The scientists suspect the trigger for intense interglacials might lie in Antarctica.
Earlier
work by the international ANDRILL program discovered recurring
intervals when the West Antarctic Ice Sheet melted. (ANDRILL, or the
ANtarctic geological DRILLing project, is a collaboration of scientists
from five nations—Germany, Italy, New Zealand, the United Kingdom and
the United States—to recover geologic records from the Antarctic
margin.)
The current Lake E study shows that some of these events match with the super interglacials in the Arctic.
The
results are of global significance, they believe, demonstrating strong
indications of an ongoing collapse of ice shelves around the Antarctic
Peninsula and at the margins of the West Antarctica Ice Sheet—and a
potential acceleration in the near future.
The Science
paper co-authors discuss two scenarios for future testing that could
explain the Northern Hemisphere-Southern Hemisphere climate coupling.
First,
they say, reduced glacial ice cover and loss of ice shelves in
Antarctica could have limited formation of cold bottom water masses that
flow into the North Pacific Ocean and upwell to the surface, resulting
in warmer surface waters, higher temperatures and increased
precipitation on land.
Alternatively,
disintegration of the West Antarctic Ice Sheet may have led to
significant global sea level rise and allowed more warm surface water to
reach the Arctic Ocean through the Bering Strait.
Lake E’s past, say the researchers, could be the key to our global climate future.
The
El’gygytgyn Drilling Project also was funded by the International
Continental Scientific Drilling Program (ICDP), the German Federal
Ministry for Education and Research, Alfred Wegener Institute,
GeoForschungsZentrum-Potsdam, the Russian Academy of Sciences Far East
Branch, the Russian Foundation for Basic Research, and the Austrian
Ministry for Science and Research.