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Field notes -- ongoing research in the geosciences
Deep
Freeze
Deep-water production in the ocean’s global
conveyor belt, driven by density changes in the surface water, may be responsible
for shifts in climate cycles, says Wallace Broecker of Columbia University’s
Lamont-Doherty Earth Observatory. In the Nov. 5 Science, Broecker and colleagues
challenge the long-held notion of a steady-state deep ocean circulation.
Broecker’s synthesis and interpretation of recent studies show Antarctica’s
formation of deep water is one-third that of the North Atlantic, but has
oscillated in the past. While Europe was getting the big chill, Antarctica
was heating up. Climate changes on the cycle of 1,500 years may be linked
to this seesaw effect. During the most recent cold spell, the Little Ice
Age, the deep-water production in Antarctica was stronger than in the North
Atlantic, Broecker says.
Under
thin ice
Naval submarines using upward-looking sonar
found thinning ice around the Arctic pole, a warming trend that may be
triggered by changes in wind patterns. Strong westerly winds have whipped
across the Arctic since the mid-1970s, instead of weaker winds that dominated
for decades before. The winds carry ice and cold surface water away from
the pole, allowing room for warmer water to seep in. The thickness of the
ice dropped 40 percent between the first study (from 1958 to 1976) and
the recent study (from 1993 to 1997) by Drew A. Rothrock of the University
of Washington in Seattle. Strong winds have dominated before, but now global
warming may be partly responsible by creating greater temperature contrasts
between the tropics and polar regions. Rothrock and colleagues published
their findings in the December issue of the journal Geophysical Research
Letters.
Cambrian's
backbone
The agnathan fish swam away from the disaster
that struck the Burgess Shale and missed its chance at being fossilized,
and awed at, as part of what is known as the Cambrian explosion. But it
may now have its chance at stardom. Simon Conway Morris of Cambridge University
and scientists from China reported in the Nov. 4 Nature their findings
of two fishlike fossils from the Lower Cambrian, about 530 million years
old. Previously the fossil record showed the first fish arriving in the
Lower Ordovician, about 480 million years ago, with only questionable evidence
of earlier arrival. The 2.5-inch-long fossils were discovered in China.
One resembles a lamprey and the other a primitive hagfish.
Christina Reed
Geotimes
Compass image courtesy of Brunton