[meteorite-list] Arctic Impact Crater Lake Reveals Interglacial Cycles in Sediments

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Tue, 11 Dec 2007 12:24:54 -0800 (PST)
Message-ID: <200712112024.MAA25604_at_zagami.jpl.nasa.gov>

http://dailyheadlines.uark.edu/11974.htm

FOR RELEASE: Tuesday, December 11, 2007

Arctic Impact Crater Lake Reveals Interglacial Cycles in Sediments
Univerity of Arkansas

FAYETTEVILLE, Ark. - A University of Arkansas researcher and a team of
international scientists have taken cores from the sediments of a
Canadian Arctic lake and found an interglacial record indicating two
ice-free periods that could pre-date the Holocene Epoch.

Sonja Hausmann, assistant professor of geosciences in the J. William
Fulbright College of Arts and Sciences at the University of Arkansas,
and her colleagues will report their preliminary findings at the
American Geophysical Union meeting this week.

The researchers traveled by increasingly smaller planes, Ski-doos and
finally sleds dragged on foot to arrive at the Pingualuit Crater,
located in the Parc National des Pingualuit in northern Quebec. The
crater formed about 1.4 million years ago as the result of a meteorite
impact, and today it hosts a lake about 267 meters deep. Its unique
setting - the lake has no surface connection to other surrounding water
bodies - makes it a prime candidate for the study of lake sediments.

Scientists study lake sediments to determine environmental information
beyond historical records. Hausmann studies diatoms, unicellular algae
with shells of silica, which remain in the sediments. Diatoms make
excellent bioindicators, Hausmann said, because the diatom community
composition changes with environmental changes in acidity, climate,
nutrient availability and lake circulation.

By examining relationships between modern diatom communities and their
environment, Hausmann and her colleagues can reconstruct various
historic environmental changes quantitatively.

However, most sediments of lakes in previously glaciated areas have
limitations - they only date back to the last ice age.

"Glaciers are powerful. They polish everything," Hausmann said. Glaciers
typically carve out any sediments in a lake bed, meaning any record
before the ice age is swept away.

However, the unique composition of the Pingualuit Crater Lake led Michel
A. Bouchard to speculate in 1989 that the sediments beneath its icy
exterior might have escaped glacial sculpting. So in May of this year,
Hausmann and her colleagues donned parkas, hauled equipment on ski-doos
and slogged through sub-zero temperatures for three weeks so they could
core sediments and collect data from the lake.

They carefully carved squares of ice out to make a small hole for
equipment, then began a series of investigations that included pulling
up a core of the topmost 8.5 meters of sediment. An echosounder
indicated that the lake bottom may have more than 100 meters of
relatively fine-grained sediments altogether. During the time since the
expedition, researchers have examined the physical, magnetic and
sedimentological properties of the sediment core.

The sediment core contains mostly faintly laminated silts or sandy mud
with frequent pebble-size rock fragments, which is typical of deposits
found in water bodies covered by an ice sheet. Sandwiched in the middle
of the faintly laminated silts and sandy mud, the researchers found two
distinct and separate layers containing organically rich material that
most likely date back well before the Holocene, representing earlier
ice-free periods. The samples they found contain the remains of diatoms
and other organic material, suggesting that they represent ice-free
conditions and possibly interglacial periods.

"There are no paleolimnological studies of lakes that cover several warm
periods in this area," Hausmann said. The terrestrial record will be
complementary to marine records or to long ice-core records from Greenland.

The international team of researchers in the field included Guillaume
St-Onge; Reinhard Pienitz, principal investigator; Veli-Pekka Salonen of
the University of Helsinki, Finland; and Richard Niederreiter, coring
expert. Please visit http://www.cen.ulaval.ca/pingualuit/index.html for
more information.

###

Contact:

Sonja Hausmann, assistant professor, geosciences
J. William Fulbright College of Arts and Sciences
(479) 575-6419, shausman at uark.edu

Melissa Lutz Blouin, director of science and research communications
University Relations
(479) 575-5555, blouin at uark.edu
Received on Tue 11 Dec 2007 03:24:54 PM PST