During the Eocene, Australia remained largely connected to Antarctica
and supposing everything is more or less right, it is reasonable that
the circumpolar current was cut of and equatorial waters were
diverted onto these shores in just the same way the gulf Stream is
diverted today. Shift all this a little bit and the landmass
available to hold a polar ice cap disappears. Certainly it was all
about geological configuration for this local phenomena to arise.
Add in the chemical changes that led to global cooling reported on
earlier this month and we have a rough outline of what took place
then.
It is clear that during the Eocene that the Ice Caps largely did not
exist although the best likely were located in Antarctica even then.
Tropical climate in
the Antarctic
by Staff Writers
Frankfurt, Germany (SPX) Aug 07, 2012
The scientists used
the drillship JOIDES Resolution to recover sediment cores off the
Antarctic coast. Drilling reached a depth of more than 1,000 m below
the sea floor. Credit: Rob Dunbar, Stanford University.
Given the predicted
rise in global temperatures in the coming decades, climate scientists
are particularly interested in warm periods that occurred in the
geological past. Knowledge of past episodes of global warmth can be
used to better understand the relationship between climate change,
variations in atmospheric carbon dioxide and the reaction of Earth's
biosphere.
An
international team led by scientists from the Goethe University and
the Biodiversity and Climate Research Centre in Frankfurt, Germany,
has discovered an intense warming phase around 52 million years
ago in drill cores obtained from the seafloor near Antarctica -
a region that is especially important in climate research.
The study published in
the journal Nature shows that tropical vegetation, including palms
and relatives of today's tropical Baobab trees, was growing on the
coast of Antarctica 52 million years ago.
These results
highlight the extreme contrast between modern and past climatic
conditions on Antarctica and the extent of global warmth during
periods of elevated atmospheric carbon dioxide levels.
Around 52 million
years ago, the concentration of the greenhouse gas carbon dioxide
(CO2) in the atmosphere was more than twice as high as today.
"If the current
CO2 emissions continue unabated due to the burning of fossil fuels,
CO2 concentrations in the atmosphere, as they existed in the distant
past, are likely to be achieved within a few hundred years",
explains Prof. Jorg Pross, a paleoclimatologist at the Goethe
University and member of the Biodiversity and Climate Research Centre
(BiK-F) in Frankfurt, Germany.
"By
studying naturally occurring climate warming periods
in the geological past, our knowledge of the mechanisms and processes
in the climate system increases. This contributes enormously to
improving our understanding of current human-induced global warming."
Computer models
indicate that future climate warming will be particularly pronounced
in high-latitude regions, i.e., near the poles. Until now, however,
it has been unclear how Antarctic terrestrial ecosystems responded in
the geological past to a greenhouse climate with high atmospheric CO2
concentrations.
The scientists working
with Prof. Pross analysed rock samples from drill cores on the
seabed, which were obtained off the coast of Wilkes Land,
Antarctica, as part of the Integrated Ocean Drilling Program
(IODP).
The rock samples are
between 53 and 46 million years old and contain fossil pollen and
spores that are known to originate from the Antarctic coastal region.
The researchers were
thus able to reconstruct the local vegetation on Antarctica and,
accordingly, interpret the presence of tropical and subtropical
rainforests covering the coastal region 52 million years ago.
In
an area where the Antarctic ice sheet borders the Southern Ocean
today, frost-sensitive and warmth-loving plants such as palms and the
ancestors of today's baobab trees flourished 52 million years ago.
The scientists'
evaluations show that the winter temperatures on the Wilkes Land
coast of Antarctica were warmer than 10 degrees Celsius at that time,
despite three months of polar night.
The continental
interior, however, was noticeably cooler, with the climate supporting
the growth of temperate rainforests characterized by southern beech
and Araucaria trees of the type common in New Zealand today.
Additional
evidence of extremely mild temperatures was provided by analysis of
organic compounds that were produced by soil bacteria populating the
soils along the Antarctic coast.
These new findings
from Antarctica also imply that the temperature difference between
the low latitudes and high southern latitudes during the greenhouse
phase 52 million years ago was significantly smaller than previously
thought.
"The CO2 content
of the atmosphere as assumed for that time interval is not enough on
its own to explain the almost tropical conditions in the Antarctic",
says Pross.
"Another
important factor was the transfer of heat via warm ocean currents
that reached Antarctica." When the warm ocean current collapsed
and the Antarctic coast came under the influence of cooler ocean
currents, the tropical rainforests including palms and Baobab
relatives also disappeared.
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