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By Peter Rejcek
The oldest ice core retrieved from Antarctica —
and the world — travels back about 850,000 years
in time, revealing eight previous ice ages. It took the
European Project for Ice Coring in Antarctica (EPICA)
more than five field seasons to drill down 3,270 meters
into the East Antarctic ice sheet.
Andrei Kurbatov and his colleagues believe that they
can retrieve a nearly limitless supply of ice for climate
research that dates back at least 2.5 million years —
located right at the surface and retrievable in a single
season.
The proverbial gold mine of old ice is located in a region
called the Allan Hills Blue Ice Area, only about an hour’s
plane ride away from McMurdo Station , the hub of the
U.S. Antarctic Program .
Snow covers most of Antarctica, but in blue ice areas,
wind scours the snow from the surface. Sublimation —
a process that turns snow immediately into water vapor
in the air — takes care of the rest. Blue ice areas
generally form where subglacial mountains obstruct ice
flow, pushing the ice below to the surface. The surface
ice closest to Allan Hills is the oldest ice and ages
Benjamin Button-style farther away one moves horizontally.
“It’s right on the surface, and if we sample
it right, we should be able to complement existing ice
core records,” said Kurbatov, an assistant research
professor at University of Maine’s Climate Change
Institute .
The first indication that Allan Hills held million-year-old
ice actually came from meteorites collected there by scientists
working on the Antarctica Search for Meteorites program
for more than three decades, according to Kurbatov. Dating
of the extraterrestrial rocks at the surface suggested
an age of at least a million years. In addition, meteorite
fragments buried in the ice just below the surface date
back about 2.5 million years.
Kurbatov said previous work by William McIntosh and Nelia
Dunbar, with the New Mexico Bureau of Geology and Mineral
Resources at New Mexico Tech , revealed an ash layer in
the blue ice that turned out to be four million years
old, further bolstering the idea that old ice was available
for the picking without multi-million-dollar ice drilling
operations.
“The whole purpose of this project is to confirm
that the ice is good for the reconstruction of climate,”
Kurbatov explained. “Once we’ve done that, technically
we could map this ice.”
Kurbatov and his team will have two field seasons to
collect samples from shallow ice cores and horizontal
trenches using a machine developed and used by McIntosh
and Dunbar about 10 years ago. The ice cutter — a
four-wheeled, steel-framed contraption that sports two
chainsaws at 45-degree angles — cuts a horizontal
trench into the ice, pushed from behind like a lawnmower.
The scientists will date the core mainly using a novel
technique comparing the stable isotope ratio of Argon-38
and Argon-40 gas bubbles trapped in the ice, developed
by colleague Michael Bender at Princeton University .
The gas measurements allow the scientists to date the
ice based on decay of the argon.
“It will probably be one of the best dates available
to us,” Kurbatov said.
If the ice proves viable — samples contain the
same sort of properties as ice cores such as trapped gas
and dust particles that provide information about past
climate — Kurbatov said the Allan Hills could prove
to be a “climate park” where investigators can
request ice of varying ages for an experiment.
“The problem with ice core records, it’s never
enough ice [for research],” he said, though stressed
that ice cores remain the “gold standard” for
climate research. “Ice cores are a crucial part of
the Antarctica science program.”
But the blue ice at Allan Hills does offer a sort of
proxy time machine for climate far beyond what’s
available today from ice cores. Based on climate records
from ocean sediment cores, which can contain tens of millions
of years of history, scientists know that ice ages used
to wax and wane on a roughly 40,000-year cycle. About
a million years ago, that became a 100,000-year cycle.
No one really knows why. And sediment cores don’t
really offer the sort of resolution — the finer details
— that researchers need to tease out an answer. That
keystone could be right underfoot in the blue ice at Allan
Hills.
“You have everything that was in the atmosphere.
You preserve it like an archive,” Kurbatov said.
“That’s why we really want to get this old ice,
and see if it can show us something interesting.”
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