A Rutgers-led study
in the journal Nature
Geoscience examined
the long-term cooling
that occurred before
the recent global warming.
"The findings of our study,
if substantiated, raise more
questions than they answered,"
said senior author
Yair Rosenthal, a professor
in the Department of Marine
and Coastal Sciences in the
School of Environmental
and Biological Sciences
at Rutgers University
-New Brunswick.
"If the cooling is not due to
enhanced Himalayan rock
weathering, then what
processes have been
overlooked?"
For decades, the consensus
hypothesis has been that
the collision of the Indian
and Asian continents and
uplifting of the Himalayas
brought fresh rocks to the
Earth's surface, making them
more vulnerable to weathering
that captured and stored
carbon dioxide - a greenhouse gas.
That hypothesis is unproven.
Lead author Weimin Si,
challenged the hypothesis
and examined deep-sea
sediments rich with
calcium carbonate.
Over millions of years,
the weathering of rocks
captured carbon dioxide
and rivers carried it
to the ocean as dissolved
inorganic carbon.
The dissolved carbon
was used by algae
to build their calcium
carbonate shells.
When algae die,
their skeletons fall
on the seafloor and
get buried, locking
carbon from the
atmosphere in
deep-sea sediments.
After studying dozens
of deep-sea sediment
cores through an
international ocean
drilling program,
Si found that calcium
carbonate in shells
decreased significantly
over 15 million years,
which suggests that
rock weathering may not
be responsible for the
long-term cooling.
The scientists
also found
that algae called
coccolithophores
adapted to the
carbon dioxide decline
over 15 million years
by reducing their
production of
calcium carbonate.
This reduction was not
taken into account
in previous studies.
Many scientists believe
that ocean acidification
from high carbon dioxide
levels will reduce the
calcium carbonate in algae,
especially in the near future.
The data suggest
the opposite occurred
over the 15 million years
before the current
global warming spell.
Rosenthal's lab
is now studying
the evolution of
calcium and
other elements
in the ocean.