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Climate of the Past An interactive open-access journal of the European Geosciences Union
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Discussion papers
https://doi.org/10.5194/cp-2018-117
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/cp-2018-117
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 12 Sep 2018

Research article | 12 Sep 2018

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Climate of the Past (CP).

Precipitation δ18O on the Himalaya-Tibet orogeny and its relationship to surface elevation

Hong Shen and Christopher J. Poulsen Hong Shen and Christopher J. Poulsen
  • Department of Earth and Environmental Sciences, University of Michigan, Ann Arbor, 48109, USA

Abstract. The elevation history of the Himalaya-Tibet orogen is central to understanding the evolution and dynamics of both the Indian-Asia collision and the Asian monsoons. The surface elevation history of the region is largely deduced from stable isotope (δ18O, δD) paleoaltimetry. This method is based on the observed relationship between the isotopic composition of meteoric waters (δ18Op, δDp) and surface elevation, and the assumption that precipitation undergoes Rayleigh distillation under forced ascent. Here we evaluate how elevation-induced climate change influences the δ18Op-elevation relationship and whether Rayleigh distillation is the dominant process affecting δ18Op. We use an isotope-enabled climate model, ECHAM-wiso, to show that the Rayleigh distillation process is only dominant in the monsoonal regions of the Himalayas when the mountains are high. When the orogen is lowered, local surface recycling and convective processes become important as forced ascent is weakened due to weaker Asian monsoons. As a result, the δ18Op lapse rate in the Himalayas increases from around −3‰/km to above −0.1‰/km, having little relationship with elevation. On the Tibetan Plateau, the meridional gradient of δ18O decreases from ~1‰/° to ~0.3‰/° with reduced elevation, primarily due to enhanced sub-cloud re-evaporation under lower relative humidity. Overall, we report that using δ18Op or δDp to deduce surface elevation change in the Himalaya-Tibet region has severe limitations and demonstrate that the processes that control δ18Op vary by region and with surface elevation. In sum, we determine that the application of δ18O-paleoaltimetry is only appropriate for 7 of the 50 sites from which δ18O records have been used to infer past elevations.

Hong Shen and Christopher J. Poulsen
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Status: final response (author comments only)
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Hong Shen and Christopher J. Poulsen
Hong Shen and Christopher J. Poulsen
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Latest update: 16 Nov 2018
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Short summary
The stable isotopic composition of water (δ18O) preserved in terrestrial sediments has been used to reconstruct surface elevations. The method is based on the observed decrease in δ18O with elevation, attributed to rainout during airmass ascent. We use a climate model to test the δ18O-elevation relationship during Tibetan-Himalayan uplift. We show that δ18O is a poor indicator of past elevation over most of the region because processes other than rainout are important when elevations are lower.
The stable isotopic composition of water (δ18O) preserved in terrestrial sediments has been used...
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