What melted ice age?
London: It wasn't only warm summers in the northern hemisphere, but also in the southern hemisphere that melted the ice age, a new study has revealed.
An international team, led by Dr Russell Drysdale of Newcastle University, has found that warm summers in both the northern and southern hemispheres may have ended the ice age, the 'Science' journal reported.
Previous research had identified precisely when these
orbital "wobbles" occurred, but it had not been possible to
accurately date the records of the Earth's response to them,
which are found in marine sediment on the ocean floors.
Dr Drysdale said ocean sediment cores contain a wealth of information about past global climate but beyond about 50,000 years ago it is difficult to determine the exact age of these sediments.
"To overcome this, we studied isotope variations in three stalagmites collected from an Italian cave, and found that these variations relate to ocean temperature changes recorded in sediment cores from the nearby sea floor.
"Stalagmites from limestone caves can be very precisely dated using trace amounts of uranium incorporated within their structure.
"We applied the accurate timescale of the stalagmite
record to the sea floor sediment data. A key property of
sea-floor sediments is that they detect the growth and decay
of ice sheets," Dr Drysdale said.
Dr Drysdale added: "So we have effectively provided an
accurate timescale for the collapse of the ice sheets that
ended the penultimate ice age. This collapse started at around
141,000 years ago.
"This is as much as 8000 years earlier than previously
thought too early to be caused by stronger northern hemisphere
summers alone, which is the prevailing theory," .
According to the researchers, the findings support the
theory that the changes were linked to increases in the angle
of the Earth's tilt.
"At the time the glacial period ended the Earth's tilt
angle was increasing. Higher tilt angles increase the total
solar energy reaching the poles of both hemispheres, where the
glacial ice sheets are positioned. This makes summers warmer
in both hemispheres in a given year.
"This mechanism has been suggested previously but up
until now we have lacked a precisely dated record to test it.
Our results support this mechanism and rule out conventional
theory of ice ages being driven by changes in northern
hemisphere summer sunlight alone.
"If anything, there are indications that the southern
hemisphere may have a more important role than that of the
northern hemisphere," Dr Drysdale said.