The research, which examined sediment core samples taken from salt
marshes in southern Australia's Tasmania island, used geochemistry to
establish a chronology of sea level changes over the past 200 years.
Sea levels in the southwest Pacific started
rising drastically in the 1880s, with a notable peak in the 1990s
thought to be linked to human-induced climate change, according to a
new study.
The research, which examined
sediment core samples taken from salt marshes in southern Australia's
Tasmania island, used geochemistry to establish a chronology of sea
level changes over the past 200 years.
Patrick Moss, from the University
of Queensland, said major environmental events which impacted the ocean
such as the introduction of unleaded petrol and nuclear tests, showed up
in the samples and were used for dating.
The chronology revealed a major
jump in sea levels around 1880 after 6,000 years of relative stability,
Moss said, with peaks in the 1910s and 1990s - the latter of which
appeared to be linked to human activity.
“Overall, over the past 200 years
or so, sea levels have increased by about 20 centimetres (eight
inches),” Moss told AFP on Thursday.
The first peak coincided with an
end to what was known as the Little Ice Age, “a 500 or so year period of
slightly cooler conditions that ended roughly around 1850” and saw
glaciers around the world retreat.
Sea
levels in the southwest Pacific rose at four times the average
20th-century rate between 1900 and 1950, according to the study.
That was followed by a period of
“relative quiet” broken by a second spike in 1990 which saw sea levels
rise at a rate that defied projections.
“The natural climatic factors seem
to be not as apparent and anthropogenic climate change seems to be the
key possible culprit,” said Moss.
The study, which also involved
researchers from Britain and New Zealand and was published in the
journal “Earth and Planetary Science Letters”, found that sea levels had
risen much more in the southwest Pacific than elsewhere.
Moss said a large ice melt was
like a “fingerprint” which could be tracked across the Earth's surface,
and the study had determined that the water which had caused the rising
Pacific sea levels had come from the northern hemisphere.
The Arctic's Greenland ice sheet
looked to be the primary source, along with “mountain glaciers in
Alaska, western North America and the Canadian Arctic,” he said.
Most
scientists have until now said the sea level rise in recent decades is
due to thermal expansion, the expansion of water due to heating, and
from glacier melt and there is much debate as to how much Greenland is
melting.
Some pro-melt research indicates the run-off is quite recent and probably contributes only about half of the current sea level rise, but Moss suggests the melt began long ago and began to affect sea levels as much as two decades ago.
By Amy Coopes@iol.co.za
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