Modern precipitation δ¹⁸O and trajectory analysis over the Himalaya‐Tibet Orogen from ECHAM5‐wiso simulations

Abstract

Variations in oxygen isotope ratios (δ18O) measured from modern precipitation and geologic archives provide a promising tool for understanding modern and past climate dynamics and tracking elevation changes over geologic time. In areas of extreme topography, such as the Tibetan Plateau, the interpretation of δ18O has proven challenging. This study investigates the climate controls on temporal (daily and 6 h intervals) and spatial variations in present‐day precipitation δ18O (δ18Op) across the Tibetan Plateau using a 30 year record produced from the European Centre/Hamburg ECHAM5‐wiso global atmospheric general circulation model (GCM). Results indicate spatial and temporal agreement between model‐predicted δ18Op and observations. Large daily δ18Op variations of −25 to +5‰ occur over the Tibetan Plateau throughout the 30 simulation years, along with interannual δ18Op variations of ~2‰. Analysis of extreme daily δ18Op indicates that extreme low values coincide with extreme highs in precipitation amount. During the summer, monsoon vapor transport from the north and southwest of the plateau generally corresponds with high δ18Op, whereas vapor transport from the Indian Ocean corresponds with average to low δ18Op. Thus, vapor source variations are one important cause of the spatial‐temporal differences in δ18Op. Comparison of GCM and Rayleigh Distillation Model (RDM)‐predicted δ18Op indicates a modest agreement for the Himalaya region (averaged over 86°–94°E), confirming application of the simpler RDM approach for estimating δ18Op lapse rates across Himalaya.

Precipitation δ18O over the Himalaya‐Tibet orogen from ECHAM5‐wiso simulations: Statistical analysis of temperature, topography and precipitation

“…Part of the unexplained variance, especially during the monsoon season, may be due to the inability of the model, and the restrictions of the spatial correlation and multiple regression applied here, to capture this effect. This explanation is also supported by Li et al [] highlighting the importance of vapor source as a control on δ 18 O during the monsoon season.…”

“…[, ]. The cluster analysis based on variables describing only model precipitation δ 18 O variability split up the domain of the Tibetan Plateau into roughly southeast to northwest trending zones and provides empirical support for the more qualitative division based on δ 18 O values [ Li et al ]. The analysis based on the relationships between precipitation δ 18 O and temperature, precipitation, and topography (established in this study) yields two major zones in the north and south of the eastern plateau and a smaller zone between them.…”

“…Unfortunately, the analysis conducted here with different size windows for analysis around a point is not amendable to include predictors that adequately capture upstream convective activity and, hence, is the focus of our efforts using a stream trace analysis in the companion paper to this one by Li et al []. As part of this study, several other efforts have been made to quantify the effect of the rainout along the path traveled by an air mass on precipitation δ 18 O.…”

“…The same analyses as described in the previous section were carried out for different isotope zones on the Tibetan Plateau. The Tibetan Plateau has previously been subdivided into three zones based on spatiotemporal patterns of precipitation δ 18 O and their relationship to climatic controls [ Yao et al ., ; Li et al ]. In this study, we evaluate these findings and attempt to quantitatively constrain the geographical extent of the domains by subdividing the plateau using a cluster analysis and on the basis of precipitation δ 18 O variability.…”

How Important Is Meltwater to the Chamkhar Chhu Headwaters of the Brahmaputra River?

“…The predominant air flow patterns relevant to the Chamkhar Chhu are the Indian summer monsoon (ISM) and the winter westerly (Figure 2). The ISM moves moisture from its origin in the Bay of Bengal (between India and Indochinese Peninsula) northward across the Himalaya (Lang and Barros, 2002;Li et al, 2016;Kumar et al, 2018). The ISM isotope gradient was investigated using a south-north transect made from two opportunely located GNIP stations: Dinajpur, Bangladesh is located at 35 m a.s.l.…”