Stable isotopes of modern water across the Himalaya and eastern Tibetan Plateau: Implications for estimates of paleoelevation and paleoclimate

Abstract

[1] Paleoaltimetry based on stable isotopes (d 18 O and d 2 H) of paleowater from the central and northern Tibetan Plateau is challenged by the lack of a clear relationship between isotopic composition and elevation north of the Himalaya. In order to determine the environmental factor(s) responsible for temporal changes in isotopic composition revealed in the geologic record, an understanding of the modern controls on isotope evolution in the continental interior is necessary. Here, we present new d18 O and deuterium excess (d excess) data from modern surface water along a roughly south-north transect on the eastern part of the Himalaya and Tibetan Plateau. Results corroborate an inverse relationship between d18 O and elevation in the Himalaya. Northward across the plateau, there is a positive trend in meteoric water d18 O that is linear ($1.5‰ per degree latitude) and robust (R 2 = 0.94). A positive trend northward is also observed in d excess of surface water from large rivers. We show that Rayleigh distillation modified by surface water recycling can account for the observed spatial distribution of both d18 O and d excess across the plateau. HYSPLIT modeling of air parcel back trajectories suggests that air mass mixing varies from east to west across the plateau. However, isotopic trends along the plateau's eastern margin are consistent with roughly parallel transects to the west, suggesting that a local process like moisture recycling exerts control over the isotopic evolution across the entire plateau, regardless of origin of air masses. Assuming the northern Tibetan Plateau was equally far from an oceanic source during late Eocene-Miocene time, paleoelevations of the Hoh Xil Basin are recalculated to account for recycling, increasing elevation estimates by 1100-2700 m.Citation: Bershaw, J., S. M. Penny, and C. N. Garzione (2012), Stable isotopes of modern water across the Himalaya and eastern Tibetan Plateau: Implications for estimates of paleoelevation and paleoclimate,

Understanding snow hydrological processes through the lens of stable water isotopes

“…Here, the average isotope composition of precipitation shifts by 1.9‰/100/m for δ 2 H and 0.27‰100/m for δ 18 O, noting that in winter, above around 800 m asl, the precipitation is dominated by snow (Marty, 2008). Some version of this isotopic lapse rate is seen in almost all mountainous environments except on the leeward or "rain-shadow" side of mountains, which receive precipitation from clouds that have already passed over the highest elevation of the ridge and are no longer continuing to rise, keeping the cloud condensation temperature relatively stable (Bershaw, Penny, & Garzione, 2012;Dietermann & Weiler, 2013;Koeniger, Hubbart, Link, & Marshall, 2008;Moran, Marshall, Evans, & Sinclair, 2007;Wen, Tian, Weng, Liu, & Zhao, 2012;Winograd et al, 1998). Moran et al (2007) reported positive isotopic lapse rates (enrichment in heavier isotopes with increasing elevation) in snow samples on the leeward side of a glacierized valley in the Canadian Rockies (refer to Figure 4 in Moran et al (2007)), which may occur only if the warmer temperatures and hence smaller vapor-liquid or vapor-ice isotopic fractionation factors offset the "rain-out" effect.…”

Isotopic composition of daily precipitation along southern foothills of the Himalayas: impact of marine and continental sources of atmospheric moisture

“…Higher than the global average d-excess value of about 10‰ in meteoric waters originating from the Himalayas and Tibetan Plateau was often used to infer Mediterranean or more generally westerly derived vapour (Tian et al 2005;Hren et al, 2009;Jeelani et al, 2010;Bershaw et al, 2012). The observed high d-excess in rainfall was generally related to higher d-excess (ca.…”

Isotopic composition of daily precipitation along the southern foothills of the Himalayas: impact of marine and continental sources of atmospheric moisture

“…10 ‰) in meteoric waters originating from the Himalayas and Ti-betan Plateau was often used to infer Mediterranean or more generally westerly derived vapour (Tian et al, 2005;Hren et al, 2009;Jeelani et al, 2010;Bershaw et al, 2012). The observed high d-excess in rainfall was generally related to the higher d-excess (ca.…”