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Scientists have found a stalagmite in an Oregon cave that tells the story of thousands of winters in the Pacific Northwest.
"Most other ways of estimating past climate, like tree-ring data,
only tell us about summers, when plants are growing," Oxford University
researcher Vasile Ersek said in a statement. But understanding ancient
winters is also important for regions like western North America, where
chilly conditions are critical for determining water resources.
For their study, Ersek and his colleagues examined a cave formation
called a stalagmite that started forming 13,000 years ago in a cavern in
what is now Oregon Caves National Monument. During the region's damp
winters, water from the ground seeped through the cave's ceiling and
trickled onto the floor, with the drips slowly forming the stalagmite over time.
The ratio of certain oxygen and carbon isotopes (atoms of the same
element with a different number of neutrons) in these deposits provides
information on ancient climate.
The researchers' measurements of these chemical components showed that
the Pacific Northwest of recent prehistory saw rapid shifts between dry
and warm, and wet and cold periods, similar to the currently observed
Pacific Decadal Oscillation (PDO) — a pattern of climate variability
that switches between negative and positive every couple of decades. In a
positive, or warm, phase, the surface waters of the west Pacific become
cool and part of the eastern ocean warms, while the opposite occurs
during a negative, or cool, phase.
"Whilst we can't directly relate these changes to the Pacific Decadal
Oscillation, the mechanisms involved do look similar," Ersek said in a
statement from Oxford. "Getting a long-term perspective on these sorts
of natural climate variations may help us to understand the potential
for future loss of winter snow cover along the West Coast, as well as
what's happening out in the Pacific to influence other cyclical climate
events such as El Niño."
The cave's record keeping stopped before the industrial age began, the
researchers said, so the stalagmite unfortunately does not offer clues
about how human activities have influenced the winter climate.
The study was detailed this week in the journal Nature Communications.
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