other features common to such programs
may confer particularly large learning
benefits, she suggests. —B. BOWER
Gassy Bugs
Microbes may produce
propane under the sea
For decades, scientists have been puzzled
by periodic findings of ethane and propane
in sediments that they’ve pulled from deep
below the ocean floor. As far as they knew,
these gases could be produced only as petroleum is—by great heat applied to ancient,
buried organic matter. But sometimes,
ethane and propane turn up in areas where
that process seems unlikely.
A new report suggests a different source:
microbes. Bacteria and archaea within
underwater sediments could chew up
buried organic material and spew out
ethane and propane as waste products,
assert Kai-Uwe Hinrichs of the University
of Bremen in Germany, and his colleagues.
Heat can produce propane and ethane
only at spots along cracks in Earth’s crust
where the planet’s internal heat escapes but
is then trapped by thick layers of sediment
overlying the crust. Hinrichs’ team drew
sediment samples from six sites off Peru
that don’t meet these conditions. All had
thin layers of sediment, and two were far
from any cracks in the crust and therefore
insulated from Earth’s internal heat.
Nevertheless, the researchers found
ethane and propane locked in the sediments
at all six sites. Adding to the mystery, gases
at all the sites were in higher concentrations in pockets at shallow and middle
depths in the sediments than in deeper locations. If the gases had been produced by
heat, they would have been more abundant
farther down, Hinrichs notes.
The researchers conclude that the gases
at the sites must have been produced by
microbes. “When you can’t come up with
any geologic source, then biology is an obvious candidate,” Hinrichs says. The
researchers report in the Oct. 3
Proceedings of the National Academy of Sciences
that the isotopes in the ethane and propane
within the sediment are characteristic of
biologically produced materials.
Microbes under the seafloor commonly
break down organic matter to produce
methane, a gas similar to ethane and
propane. Although the researchers haven’t
isolated microbes that produce these two
gasses, they point to chemical reactions
that could produce them from materials
available in undersea sediment.
The concentration of propane in the sediments is too low for commercial use as fuel.
However, Hinrichs says that if the set of reactions producing the propane were better
understood, scientists might fine-tune it to
turn organic matter directly into propane.
The problem of the source of ethane and
propane in ocean sediments had “been
brushed under the carpet,” says John
Parkes of Cardiff University in Wales. The
new research “is like a breath of fresh air,”
he says. The suggestion of a biological
source of the gases is reasonable but still
unproved, he adds. In particular,
researchers must demonstrate that the
reaction that they propose takes place in
undersea microbes. —J. REHMEYER
Mixed Bag
Islet-cell transplants offer
good and bad news
Several years after receiving experimental
transplants of insulin-making cells, most
people with diabetes still need daily insulin
shots, a new study finds. But the transplanted cells that thrive in their new hosts
prevent sudden drops in blood sugar that
come without warning, a life-changing
improvement for some patients.
People with type 1, or juvenile-onset,
diabetes lose their insulin-making pancreatic cells when their immune systems
attack the clusters, or islets, housing these
cells. In a procedure called islet transplantation, physicians take islet cells from
a cadaver and infuse them into the portal
vein of a patient’s liver, where the new cells
Mystery of the Missing Heat
Upper ocean has cooled slightly in recent years, despite warming climate
Between 2003 and 2005,
the top layers of the
world’s oceans cooled
slightly, but scientists aren’t
sure where the heat went.
According to climate data
gathered worldwide, 2003,
2004, and 2005 are three of the
five warmest years since reliable record keeping of global
air temperatures began more
than a century ago. However,
oceanographic surveys suggest
that on average, the upper
750 meters of the world’s icefree oceans cooled about
0.03°C during that 3-year
period.
This cooling reverses an
oceanic-warming trend observed
since the 1950s, oceanographer
John M. Lyman and his colleagues report in the Sept. 28
Geophysical Research Letters.
Between 1993 and 2003, the
average temperature of the
upper layers of the icefree ocean
rose about 0.09°C, they note.
The newly documented cooling occurred throughout the top
750 m of ocean and seems to
have extended to deeper waters
as well, says study coauthor
Josh K. Willis, an oceanographer
now at NASA’s Jet Propulsion
Laboratory in Pasadena, Calif.
Data used in the new analysis
were gathered by buoys tethered in deep water, instruments
towed by or dropped from ships,
and an armada of robotic
probes, says Lyman, who’s at
the National Oceanographic and
Atmospheric Administration
(NOAA) laboratory in Seattle.
While the top layers of the
ocean have cooled slightly overall, some limited areas have
warmed, says coauthor
Gregory C. Johnson, also of
NOAA in Seattle. The cooling
trend, as well as its patchiness,
probably results from variations
in climate cycles such as the
Pacific Decadal Oscillation, he
notes.
“Even within a long-term
warming trend, you can have
short-term drops in [ocean]
temperature due to year-to-year variability,” says Lyman.
Scientists are working to identify where the heat went. One
possibility: It may have moved to
the deepest layers of the ocean.
The cooling of surface waters
would cause them to contract,
triggering a small drop in sea
level, says Willis. But satellite
data suggest that sea level is still
rising. So, the missing heat may
have gone deep, causing waters
there to expand and prevent a
decline in sea level. However,
“it’s hard to envision a way to
put that much heat down deep
so quickly,” says Willis.
In another scenario under
consideration, the missing heat
may have radiated into space.
However, satellite observations
don’t support that notion, says
Bruce A. Wielicki, a physicist at
NASA’s Langley Research Center
in Hampton, Va. Yet another possibility is that the heat warmed
some of the waters in polar
regions and promoted melting of
the ice cover there, he notes.
“We have a few more pieces
to unravel” about where the heat
has gone, comments Sarah T.
Gille, an oceanographer at
Scripps Institution of Oceanography in La Jolla, Calif. “It’s a real
conundrum.” —S. PERKINS
