Rise of Tibetan Plateau
Sunday, 26. August 2007, 08:02:07
The Tibetan Plateau is responsible for the monsoons in India. The rise of the Tibetan Plateau started when the Indian tectonic plate slammed into the Eurasian plate some million years ago, but not all areas of the Tibetan Plateau rose at the same time, and we do not know when the monsoon circulation began.
A couple of scientists have looked at lipids preserved in ancient lake sediment that originated in plants growing in the surrounding watershed. Lipids are substances such as a fat, oil or wax that dissolves in alcohol but not in water. Lipids contain carbon, hydrogen and oxygen. 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. The scientists were mainly interested in the hydrogen in these lipids. Hydrogen is preserved in the molecules and the hydrogen isotopic composition is preserved. Hydrogen has three naturally occurring isotopes. Hydrogen is the only element that has different names for its isotopes in common use today, namely Hydrogen (“protium” is only rarely used) (1H), deuterium (2H) and tritium (3H).
The researchers are interested in the ratio found between regular hydrogen and deuterium, hydrogen that contains both a proton and neutron in its nucleus and is heavier than normal hydrogen. This hydrogen ratio can disclose where the plants were growing because as air masses rise on the side of a mountain, water, which contains hydrogen, rains out of the air. A proportionally larger amount of deuterium rains out leaving air at higher elevations with a higher percentage of normal hydrogen. The composition of the water that plants take up from the ground is a reflection of the rainwater that falls in that area, so the hydrogen incorporated into the plants can tell us the hydrogen ratio of the rainwater. (This is similar to what I told about oxygen isotopes in my post on Climate Change and Scientific Language) - only here we are talking about delta D (∂D) instead of delta 18O (∂18O)).
By looking at the hydrogen isotope ratios of plants growing at various elevations today and the hydrogen isotope ratios in the water, the correlation between elevation and hydrogen isotope ratio can be established.
To check their approach, the researchers used a set of three samples from two locations on the Tibetan Plateau. In one location, a pair of samples came from the Miocene (about 35 million years of age) and a much earlier time in the Eocene (8 to 6 million years of age). In the other location, a Miocene sample was paired with previous results by other scientists on Eocene rocks. Two of these samples had elevations previously assigned, using similar analysis of oxygen isotopes taken from carbonates like limestone. The third, a Miocene sample, had an unknown elevation. The two known elevation samples allowed the researchers to test the accuracy of their method.
When the researchers compared the results from their two samples to the elevations derived from carbonate oxygen isotope testing, they found 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.
Knowing that the northern portion of the plateau rose later can help climatologists who try to model ancient climate. This knowledge can also help those who model the ancient biological world because different plant communities grow at different elevations because of the differing rainfall and temperatures.
Based on news of 20 August 2007 from Penn State University at:
A couple of scientists have looked at lipids preserved in ancient lake sediment that originated in plants growing in the surrounding watershed. Lipids are substances such as a fat, oil or wax that dissolves in alcohol but not in water. Lipids contain carbon, hydrogen and oxygen. 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. The scientists were mainly interested in the hydrogen in these lipids. Hydrogen is preserved in the molecules and the hydrogen isotopic composition is preserved. Hydrogen has three naturally occurring isotopes. Hydrogen is the only element that has different names for its isotopes in common use today, namely Hydrogen (“protium” is only rarely used) (1H), deuterium (2H) and tritium (3H).
The researchers are interested in the ratio found between regular hydrogen and deuterium, hydrogen that contains both a proton and neutron in its nucleus and is heavier than normal hydrogen. This hydrogen ratio can disclose where the plants were growing because as air masses rise on the side of a mountain, water, which contains hydrogen, rains out of the air. A proportionally larger amount of deuterium rains out leaving air at higher elevations with a higher percentage of normal hydrogen. The composition of the water that plants take up from the ground is a reflection of the rainwater that falls in that area, so the hydrogen incorporated into the plants can tell us the hydrogen ratio of the rainwater. (This is similar to what I told about oxygen isotopes in my post on Climate Change and Scientific Language) - only here we are talking about delta D (∂D) instead of delta 18O (∂18O)).
By looking at the hydrogen isotope ratios of plants growing at various elevations today and the hydrogen isotope ratios in the water, the correlation between elevation and hydrogen isotope ratio can be established.
To check their approach, the researchers used a set of three samples from two locations on the Tibetan Plateau. In one location, a pair of samples came from the Miocene (about 35 million years of age) and a much earlier time in the Eocene (8 to 6 million years of age). In the other location, a Miocene sample was paired with previous results by other scientists on Eocene rocks. Two of these samples had elevations previously assigned, using similar analysis of oxygen isotopes taken from carbonates like limestone. The third, a Miocene sample, had an unknown elevation. The two known elevation samples allowed the researchers to test the accuracy of their method.
When the researchers compared the results from their two samples to the elevations derived from carbonate oxygen isotope testing, they found 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.
Knowing that the northern portion of the plateau rose later can help climatologists who try to model ancient climate. This knowledge can also help those who model the ancient biological world because different plant communities grow at different elevations because of the differing rainfall and temperatures.
Based on news of 20 August 2007 from Penn State University at:
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