Arctic melt third
highest since ’79
this year’s sea ice minimum
reflects polar warming trend
By Alexandra Witze
The verdict is in on this year’s Arctic
sea ice melt: third worst since satellites
began keeping track of the northern
polar cap in 1979.
Satellites and scientists continually
monitor the Arctic Ocean’s skin of
ice, which melts back in summer and
expands again in winter. Researchers
have watched the seasonal ice decline
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with increasing alarm, especially after
the summer of 2007 brought a record-breaking minimum. Ice extent recovered
a bit in 2008 and 2009, but the long-term
trend is unmistakable.
On September 15, the National Snow
and Ice Data Center in Boulder, Colo.,
announced that this year’s ice apparently
reached its minimum five days earlier,
when it covered 4.76 million square kilometers. At its summer low, ice has covered
less than 5 million square kilometers in
three of the past four years — an arbitrary
cutoff, but an indicator of how the entire
ice ecosystem appears to be changing.
How much sea ice remains each year
depends on a complex mix of factors
including atmospheric patterns, ocean
and air temperature and winds (SN:
6/19/10, p. 22). This August, for instance,
high pressure over the Beaufort Sea
meant that ice began breaking up rapidly
there compared with the previous month.
Van Mooy expressed surprise at the
amount of gas that the new report mea-
sured in the plumes. But then again, he
adds, “It’s amazing how little we still
know about what’s down there,” espe-
cially regarding the gases contained in
the spill plume. “This is the first paper
that really takes that issue head-on.”
Another team has used a new tech-
nique to provide what may be a more
accurate estimate of the total release of
oil from the damaged well. By following
the movement of billows in the plume
visible in two snippets of
seafloor video, Timothy
Crone and Maya Tolstoy
of Columbia University
gauged the minute-by-
minute flow of oil. Their
projected total — 5. 2 mil-
lion barrels by the well’s
shutdown on July 15—
appears online in Science
September 23. The figure
slightly exceeds an earlier
federal estimate.
ultimately come from bacterial metabolism of the gases,” Valentine projects.
Microbes were not consuming much
methane, a gas molecule that
is biochemically much harder
to crack than propane and
ethane. That suggests that the
most digestible components
of the plumes were the first to
be attacked by microbes.
The new research “is quite
solid and something people
will be taking seriously,” says
Benjamin Van Mooy, a chemical oceanographer at the
Woods Hole Oceanographic
Deepwater Horizon’s
spill leaked large
amounts of natural
gas, a study finds.
Institution in Massachusetts. He was part of a team
that recently reported finding substantial undegraded
oil in the Gulf’s deep-sea plumes.
One big concern since
the initial discovery of
deep-sea hydrocarbon
plumes has been what will
happen to oxygen concentrations near
the seabed. Some scientists have questioned whether fish-suffocating dead
zones might develop. But a September 7
federal study looked for evidence of such
oxygen deprivation in zones affected by
plumes and found none.
Natural gas dominates Gulf plumes
microbes are degrading easily digested hydrocarbons first
By Janet Raloff
The plumes that formed in the Gulf of
Mexico’s depths this spring and summer
in the aftermath of the BP oil well blowout were actually only about one-third
oil, scientists estimate, with the remainder consisting of natural gas.
In June, marine microbes were primarily feeding on propane and ethane
gases in the plumes, researchers report
online in Science September 16.
“We estimate that there’s about two
times as much gas sitting in those sub-surface plumes as there is oil—and
there’s about a million barrels of oil
in them,” says David Valentine of the
University of California, Santa Barbara,
speaking by phone from a National Oceanic and Atmospheric Administration
research vessel in the Gulf.
Chemists had been trying to estimate
how much oxygen might disappear as
microbes degraded BP’s spilled oil. It
turns out that the oil is only part of the
issue. “Probably 66 to 75 percent of the
oxygen loss — maybe even a bit more — will
