sheet may be blamed for warming
Jan 27: A new study by geoscientists has suggested that the
release of natural gas by carbon-hungry bacteria trapped deep
in the rock beneath ice sheets contributed to global warming
observed during the ice age.
study also helps explain high levels of methane in the atmosphere
that occurred between ice ages, a trend recorded in ice cores
taken from Greenland and Antarctica.
to Steven Petsch, a geoscientist at the University of Massachusetts
Amherst and the author of the study, natural gas, which is
mostly methane, was released from the shale into the atmosphere.
digested the carbon in the rocks and made large amounts of
natural gas in a relatively short time, tens of thousands
of years instead of millions," said Petsch.
suggests that it may be possible to seed carbon-rich environments
with bacteria to create natural gas reservoirs," he added.
used the chemistry of water and rock samples from the Antrim
shale, which sits like a bowl beneath northern Michigan in
the US, to recreate the past. For most of its history, the
Antrim Shale contained water that was too salty to allow bacteria
areas rich in natural gas showed an influx of fresh water
that was chemically different from modern rainfall. "This
water, which is similar to melt water from glaciers formed
during the ice age, was injected into the rock by the pressure
of the overlying ice sheets," said Petsch.
melt water diluted the salt water already present in the shale,
allowing the bacteria to thrive and quickly digest available
carbon. The natural gas they produced was chemically similar
to the surrounding water and had a unique carbon chemistry
that proved its bacterial origin.
to the study, at least 75% of the gas was released into the
atmosphere as the ice sheets retreated, adding to methane
from other sources such as tropical wetlands.
methane from the Antrim Shale accounts for a small fraction
of the rise in methane observed between ice ages, there are
many natural gas deposits that were formed in the same geologic
setting. The cumulative effect may have caused large emissions
of methane to the atmosphere.