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Arctic
Average Ice Thickness
1958-
10 Feet
1999- 5.5 Feet
Scientists analyzing
decades of data from Arctic Sea ice recently reported a significant
reduction in the thickness of the ice during the last decade. The scientists
found a decrease in sea ice all across the Arctic Ocean and that corresponds
to previously reported evidence that the Arctic climate is warming,
according to Dr. D. Andrew Rothrock of the University of Washington and
colleagues. "Rothrock's work is the first confirmation that the ice is
thinning," says geophysicist Terry Tucker of the Cold Region Research
and Engineering Lab in Hanover, N.H.
A report on the
data, Thinning of the Arctic Sea-Ice Cover, was published in the Dec. 1,1999
issue of Geophysical Research Letters.
The Scientific
Ice Expeditions (SCICEX) program, which consisted of six extended voyages, acquired
the data using nuclear submarines.
SCICEX
(Scientific Ice Expeditions) Collaboration between the US Navy and civilian
scientists for environmental research in the Arctic SCICEX was a 5 year
program (1995-1999) in which the Navy made available a Sturgeon-class,
nuclear powered, attack submarine for unclassified science cruises to the
Arctic Ocean. Beginning with a test cruise in 1993, civilian scientists
together with Navy personnel have collected a variety of information on the
geology, physics, chemistry and biology of this critical region. The
unmatched mobility of submarines in ice covered oceans has allowed data to
be collected from over 100,000 miles of shiptrack in the Arctic providing
samples from some regions that have never before been visited.
USS
Archerfish SSN 678
This study analyzed data from three
autumn cruises: USS Pargo in 1993, USS Pogy in 1996 and USS Archerfish in
1997.The main focus of the expeditions has been the climate. Sometime around
1990, warmer waters from the Atlantic spilled over an undersea mountain
ridge, pushing back the cooler Pacific water. The boundary between Atlantic
and Pacific waters has remained shifted since then, and temperatures in the
deep Arctic waters, a thousand feet below the surface, have risen 1 to 2
degrees Fahrenheit.
USS
Hawkbill SSN 666
In oceanographic terms,” Muench says,
“that’s a pretty massive change. The
Arctic is a unique ocean. It plays a pivotal role in global climate, and we
know very little about it.”
There appear to be related consequences: ice sheets
are noticeably thinner. Alaskan permafrost is melting.
The changing ocean currents and shifting winds
could eventually trigger changes throughout the globe. For instance, if the
ice sheets melted entirely, the oceans would absorb much more heat,
accelerating global warming. Also, theGreenland/Iceland region of the North
Atlantic Ocean is vital to the circulation of the world’s oceans. It is
here that warm water from the tropics gets cold and dense enough to sink,
maintaining the conveyor-like circulation that brings heat from the tropics
towards the poles. An influx of fresh water from melting Arctic sea ice
would decrease the density of the upper water and so might slow down this
circulation, conferring a colder climate on the North Atlantic region.
Scientists
measuring the Arctic Ice
The average draft
of the sea ice (its thickness from the ocean surface to the bottom of the
ice pack) has declined by 4.3 feet, or 40 percent, since the first
measurements were made in 1958, said the scientists. The thickness of the
ice was about 10 feet between 1958-1976,the current thickness is about 5.5
feet. The present
analysis, shows a widespread decrease in ice draft within the central
Arctic Ocean, with the strongest decrease occurring in the eastern Arctic.
Not only is the ice cover thinner in the 1990s than earlier, it appears to
be continuing to decline in some regions through four years of SCICEX
cruises at a rate of about 4 inches(0.1 m)/yr. The study is
funded by the National Science Foundation, the Office of Naval Research and
NASA. The loss of a large ice mass over the northern polar region would have
a dramatic impact on the global climate system. Snow and ice help to cool
the Earth by reflecting energy from the Sun - up to 80% - straight back out
into space. The sinking, cold, dense, salty water which is created as ice
forms also helps to drive ocean currents which redistribute heat around the
planet. The Arctic is the northern pathway that water travels between the
Atlantic and Pacific oceans. Its vast ice sheets bounce sunlight back into
space, creating a cooling effect for the
planet.
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