All areas of Tibetan Plateau did not rise simultaneously

All areas of the Tibetan Plateau did not rise at the same time, a new study by a team of US researchers has revealed.

Washington, Aug 21 : All areas of the Tibetan Plateau did not rise at the same time, a new study by a team of US researchers has revealed.

Dr. Pratigya J. Polissar, a Penn State postdoctoral fellow in geosciences, determined the past elevation of plateau locations by studying the remains of terrestrial plants that once grew there.

She said while there is no doubt that the Tibetan Plateau is responsible for the monsoons in India, scientists really don't know as to when the plateau actually rose.

"People have documented ecological changes around the edge of the plateau that may indicate when it was high, but we do not really know when the plateau rose and so we do not know when the monsoon circulation began," said Dr. Polissar.

As part of the study, the team of Polissar Katherine H. Freeman, professor of geosciences, Penn State; and David B. Rowley, professor of geophysical sciences, University of Chicago, looked at lipids preserved in ancient lake sediment that originated in plants growing in the surrounding watershed.

The lipids were once part of the waxy coating found on leaves that grew during the late Eocene about 35 million years ago and the early Miocene, 8 to 6 million years ago. These lipids are biomarkers for the plants that generated them.

"We are really interested in the hydrogen in these lipids. Hydrogen is preserved in the molecules and the hydrogen isotopic composition is preserved," said Polissar.

Analysis of three samples from two locations on the Tibetan Plateau revealed that in one location, a pair of samples came from the Miocene and a much earlier time in the Eocene.

"No one has done this before on vegetation remains. Sediments that preserve organic material do not typically contain carbonates. This method would allow us to determine elevations at locations with only organic material," said Polissar.

Comparison of the results from the two samples to the elevations derived from carbonate oxygen isotope testing, further revealed that the organic hydrogen isotope approach worked well.

The third sample, from the Miocene, showed an elevation that was much higher than the matching sample from the Eocene.

"This shows that the basin was rising between these two sample dates. Everywhere else at this time was already high, but this area was low. The whole plateau did not rise at the same time, but the northern portion rose later," said Polissar.

Polissar further said that knowing the northern portion of the plateau rose later could help climatologists trying to model ancient climate.

This knowledge could also help those who model the ancient biological world because different plant communities grew at different elevations because of the differing rainfall and temperatures, she said.

ANI