Stable Isotopes, Climate, and the Tibetan Uplift

Science Daily has an interesting story on stable isotope analysis:

Major tectonic changes on the Tibetan Plateau may have caused it to attain its towering present-day elevations — rendering it inhospitable to the plants and animals that once thrived there — as recently as 2-3 million years ago, not millions of years earlier than that, as geologists have generally believed. The new evidence calls into question the validity of methods commonly used by scientists to reconstruct the past elevations of the region.

The actual study can be found here. Basically, the researchers examined the type of carbon in the enamel of a wide variety of vertebrate fossils and the type of carbon in shells. Currently, the Tibetan Plateau is dominated by C3 plants and this is reflected in the carbon composition in the enamel and shells of the modern fauna. The carbon composition found in the teeth and shells of fossil fauna paints a different story. The fossil fauna has a significant C4 component suggesting a somewhat wetter environment from 2-25 MYA. Wang et al say:

However, if the Himalayan-Tibetan Plateau was not as formidable a barrier in the late Pliocene as it is today, a greater amount of moisture derived from the Indian Ocean could have been carried by the Indian monsoon farther inland into the Kunlun Pass Basin, which could explain the more negative water-δ18O values. The presence of a freshwater lake and the abundance of fossil vegetation in the Qiangtang Formation also imply that water was plentiful in the basin during the late Pliocene.

This leads them to suggest that:

Assuming that (1) the temperature gradient of −5 °C/km determined from the present-day conditions of the Linxia and Kunlun Pass Basins applied to the past and (2) a temperature drop of 3 °C in the areawas due to global cooling since the Pliocene…, the estimated temperature change in the basin would correspond to an elevation change of ∼2700±1600 m since the late Pliocene. This would imply that the elevation of the Kunlun Pass Basin in the late Pliocene was ∼2011±1600 m a.s.l., much lower than its present-day elevation…

This paper is the companion paper to to an earlier paper that goes into more detail on fossil vs moder fauna differences.

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