On Thin Ice..........
Nov. 17 ? Scientists mining old data have
discovered ?a major climatic signal.? The Arctic
Ocean?s ice cap has shrunk more dramatically
than anyone realized.
Comparing ice thicknesses measured by submarines
between 1958 and 1976 with measurements made this
decade, scientists found that, on average, the cap is 4.3
feet thinner.
It has lost some 40 percent of its volume.
Several earlier studies had indicated widespread
thinning. But they didn?t give a comprehensive picture.
Now a team of scientists at the University of Washington
in Seattle has sketched that picture.
A Fundamental Shift
The results, to be published in the Dec. 1 edition of
Geophysical Research Letters, are another indicator of
substantial changes in the Arctic that could impact global
weather. And they also present an intriguing mystery.
Because the data essentially cover the entire ice cap,
they indicate ?there is something fundamental going on,?
says Gary Maykut, who collaborated with D. Andrew
Rothrock and Yanling Yu on the study. This is not just
melting around the edges. It?s not a balanced situation
where ice lost in one region is made up by ice formation in
another area.
Yet ?there?s no smoking gun here,? says Maykut.
There?s nothing to tie the ice loss to any man-made or
natural global warming. Climatologists can only speculate
as to whether it?s part of a natural Arctic climatic cycle
that some researchers have identified.
For these reasons, Maykut says a more detailed study
of the data is vital. Several dozen Arctic scientists made
that plea two years ago to the US National Science
Foundation, citing factors such as a 2 degree Fahrenheit
or more warming in large parts of the Arctic Ocean. That
includes incursions of relatively warm Atlantic water well
beyond its normal seasonal range.
Currents, Climate Linked
Indeed, the behavior of Atlantic currents is of critical
importance, scientists say. Climatologists worry about
changes in current partly because of the way the Arctic
Ocean interacts with the North Atlantic, a region of huge
climatic significance.
In the normal seasonal cycle, cold Arctic water
pushing into the Atlantic sinks and flows southward. Other
currents flowing nearer the surface bring warmer water
northward. It?s a key part of the large-scale ocean
circulation that drives our present climate.
If the Arctic were to lose substantial parts of its ice
cover, though, the cold, dense water flow might be cut off
or replaced by less-dense water that would not sink,
upsetting the climate throughout much of the Northern
Hemisphere.
Evidence Under the Ice
Arctic research has picked up in this decade through
ship-based, ice-camp-based, and undersea explorations.
The Navy?s Scientific Ice Expeditions (SCICEX), which
sent research submarines under the ice cap, have played a
major role.
The Seattle team used SCICEX data gathered
between September 1993 and September 1997 in their
study.
Release of formerly secret US and Russian data also
boosts Arctic research. This gave the Seattle team the
crucial data from 1958 through 1976.
Meanwhile, Maykut warns against making too much of
the findings just yet. The researchers lumped the early
data together to get an average picture of the ice cap.
They did the same with the SCICEX data. He says:
?Basically, what we have are two data points [with
nothing in between]. And now we say, ?Wow!
Something?s happening.? ?
Navy Measurements Sought
That?s not enough to uncover trends or causes. It?s just
enough to justify further research. What?s needed for that
research, the team says, is for the Navy to release the
detailed ice-thickness measurements its submarines have
made over the past 40 years.
What?s been available so far are anonymous averages
for submarine runs. These hide the identity of which
submarine took which measurements at specific points
and at specific times. If Russian technicians had that
information, they might be able to identify the acoustic
signature of specific American submarines, some of which
are still in service.
That?s the kind of security issue that has kept the
detailed ice-thickness data locked up. Maykut says he
thinks the issue is becoming obsolete, especially as older
submarines leave service, and he expects more of the
crucial data to become available over the next few years. |
