In Antarctica, at the end of January, a research team investigating the last 100,000 years of Earth's climate history reached an important milestone completing the main ice core to a depth of 10,928 feet at West Antarctic Ice Sheet Divide (WAIS). The project will be completed over the next two years with some additional coring and borehole logging to obtain additional information and samples of the ice for the study of the climate record contained in the core.
As part of
the project, begun six years ago, the team, funded by the National Science
Foundation (NSF), has been drilling deep into the ice at the WAIS Divide site
and recovering and analyzing ice cores for clues about how changes in the
concentration of greenhouse gases in the atmosphere have influenced the Earth's
climate over time.
most-recent milestone was reached at a depth of about 2 miles deep, creating
the deepest ice core ever drilled by the United States, and the second deepest
ice core ever drilled by any group, second only to the ice core drilled at
Russia's Vostok Station as part of a joint French/U.S./Russian collaboration in
improving our understanding of how natural changes in greenhouse gas influenced
climate in the past, the science community will be able to do a better job of
predicting future climate changes caused by the emissions of greenhouse gases
by human activity," says Kendrick Taylor, chief scientist for the WAIS
Divide Ice Core Project.
drilling site is about 600 miles from the South Pole, at an ice divide (which
is analogous to a watershed divide) in West Antarctica,
where the ice is flowing out to the sea in opposing directions.
location was selected because it is the best place on the planet to determine
how greenhouse gases have changed during the last 100,000 years," says Taylor. Since it began,
the WAIS Divide Ice Core Project has continuously collected ice from the
surface down to a depth of t miles. The ice at this depth fell as snow about
100,000 years ago. The high annual snowfall at the site enables individual
annual layers of snowfall to be identified and counted (much like counting tree
rings) back to about 40,000 years. Below that, the layers become too compressed
to allow annual layers to be resolved. Scientists hope for at least decadal
resolution to this point, sufficient for the science goals to be achieved.
cores are 5-inch-diameter cylinders of ice collected from deep in the ice
sheet. Over time, the ice has formed when snow was compacted at the surface by
subsequent snowfall. The compacted snow contains dust, chemicals and
atmospheric gases, which are trapped in the ice.
and other impurities in the ice are indicators of past climate, and the gas
contained in air bubbles is a sample of the ancient atmosphere. The deeper the
ice, the further back in time measurements can be made.
to measuring what the atmospheric concentrations of carbon dioxide, methane and
other gases were in the past, the research team also can determine what the
surface air temperature was in the past by studying changes in the isotopic
composition of the water that makes up the ice. The past atmospheric
concentrations of the gases krypton and xenon are used to determine what the
average temperature of the ocean was in the past.
2-mile-long ice core is cut into 3 feet-long pieces of ice and sent by ship and
refrigerated truck to the NSF National Ice Core Laboratory in Denver. The ice is cut into smaller samples,
and sent to 27 investigators around the United States, who make the
ice cores have shown that the current level of greenhouse gases is greater now
than at any time during the last 650,000 years, and that concentrations today
are increasing at the fastest rate," says Taylor. "This increase is caused by
human activity, and is forcing the climate into a configuration that no human
has ever experienced."
Divide Ice Core Project is specifically investigating the small timing offsets
between past changes in the atmospheric concentration of greenhouse gases and
changes in temperature. By understanding these timing offsets, the research
team can determine the role that changes in ocean circulation had in the
release of carbon dioxide from the ocean and how an increase in carbon dioxide
in the atmosphere warms the planet.
drilling ceased 328 feet above the contact between the ice and the underlying
rock, to avoid contaminating a possible water layer at the ice-rock contact.
The basal water system may consist of water-saturated, ground-up rock, and has
not been exposed to the earth's surface for millions of years. It may harbor a
unique and pristine biological environment that the U.S. Antarctic Program does
not wish to contaminate.
taken by the WAIS Ice Core Drilling Project is crucial for fine-tuning the
researchers' understanding of how the oceans, atmosphere and climate interact
during climate changes. A Danish-led team recovered an ice core from Greenland this past summer with similar time resolution
to the WAIS Divide record. The two cores provide an opportunity to compare the
response of the northern and southern hemispheres to climate changes. The
Greenland ice core cannot be used to study changes in the atmospheric
concentration of carbon dioxide because there is too much dust in the Greenland ice, which decomposes and releases
non-atmospheric carbon dioxide into the ice.
Office of Polar Programs funds this research, primarily through its Antarctic
still have two more field seasons of work to complete the project, and reaching
this goal should allow us to complete the project on schedule," says Julie
Palais, program director. "In addition, we are hoping to get as long a
record as possible from this site, and getting all of the ice we planned on
this year will allow the science community to do the work that they are funded
to do. Drilling the ice core is just the first step in the process, albeit a
very important one."
Ice Cores Yield Rich History of Climate Change
February 9, 2011