Scientists using
ice-penetrating radar data collected by NASA's Operation IceBridge and earlier
airborne campaigns have built the first comprehensive map of layers deep inside
the Greenland Ice Sheet, opening a window on past climate conditions and the ice
sheet's potentially perilous future. This new map allows scientists to
determine the age of large swaths of the second largest mass of ice on Earth,
an area containing enough water to raise ocean levels by about 20 feet. Greenland's
ice sheet has been losing mass during the past two decades, a phenomenon
accelerated by warming temperatures. Scientists are studying ice from different
climate periods in the past to better understand how the ice sheet might
respond in the future. These cylinders of ice drilled from the ice sheet hold
evidence of past snow accumulation and temperature and contain impurities such
as dust and volcanic ash compacted over hundreds of thousands of years. These
layers are visible in ice cores and can be detected with ice-penetrating radar.
Ice-penetrating radar works by sending radar signals into the ice and recording
the strength and return time of reflected signals. From those signals,
scientists can detect the ice surface, sub-ice bedrock and layers within the
ice. New techniques used in this study allowed scientists to efficiently pick
out these layers in radar data.
Prior studies
had mapped internal layers, but not at the scale made possible by these newer,
faster methods. Another major factor in this study was the scope of Operation IceBridge's
measurements across Greenland, which included flights that covered distances of
tens of thousands of kilometers across the ice sheet. IceBridge's flight lines
often intersect ice core sites where other scientists have analyzed the ice's
chemical composition to map and date layers in the ice. These core data provide
a reference for radar measurements and provide a way to calculate how much ice
from a given climate period exists across the ice sheet, something known as an
age volume. Scientists are interested in knowing more about ice from the Eemian
period, a time from 115,000 to 130,000 years ago that was about as warm as
today. This new age volume provides the first data-driven estimate of where
Eemian ice may remain. Comparing this age volume to simple computer models
helped the study's team better understand the ice sheet's history. Differences
in the mapped and modeled age volumes point to past changes in ice flow or
processes such as melting at the ice sheet's base. This information will be
helpful for evaluating the more sophisticated ice sheet models that are crucial
for projecting Greenland's future contribution to sea-level rise.
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