Evaporative enrichment of oxygen-18 and deuterium in lake waters on the Tibetan Plateau

Abstract

Stable isotopes (d 18 O and dD) are useful tracers for investigating hydrologic and climatic variability on a variety of temporal and spatial scales. Since the early isotopic studies on mountainous glaciers in the late 1960s, a great deal of information has been generated on the isotopic composition of rainfall, snow, ice, surface waters, and lake carbonate sediments across the Tibetan Plateau. However, measurements of d 18 O and dD values of lake water are scarce. Here we present a new dataset of d 18 O and dD values of lake waters collected from 27 lakes across the plateau during a reconnaissance survey in summer 2009. d 18 O and dD values of lake water range from-19.9 to 6.6% and from-153 to-16%, respectively. The average values of d 18 O and dD are-6.4 and-72%, considerably greater than those of precipitation observed in this region. The derived Tibetan lake water line, dD = 5.2d 18 O-38.9, is significantly different from the global meteoric water line. Most of the lakes, including some freshwater lakes, contain water with negative values of d-excess (d). There is a negative correlation between d and total dissolved solids (TDS). Each of these findings indicates that evaporationinduced isotopic enrichment prevails in Tibetan lakes. Moreover, we develop an isotope modeling scheme to calculate E/P ratios for Tibetan lakes, using a combination of existing isotopic fractionation equations and the Rayleigh distillation model. We use the intersection of the local evaporation line and GMWL as a first approximation of d 18 O and dD values of lake water inputs to infer an E/P ratio for each lake. Our modeling calculations reveal that although variable from lake to lake, the water budget across the plateau is positive, with an average E/P of 0.52. This is in good agreement with other observational and model data that show varying degrees of increases in lake size from satellite imagery and significant decreases in lake salinity in many lakes on the plateau over the last several decades. Together with the new isotopic dataset, the proposed modeling framework can be used to examine and quantify past changes in a lake's hydrologic balance from the isotopic record of downcore carbonate sediments in the region.

Deuterium‐excess determination of evaporation to inflow ratios of an alpine lake: Implications for water balance and modeling

“…The LEL in Cona Lake is δ 2 H = 6.67δ 18 O − 20.37 ( n = 145, R 2 = 0.91), with a much lower slope and intercept than that of LMWL, implying evaporative enrichment of the lake water. The slope and intercept of the LEL here are similar to that of LEL in through‐flow lakes in other parts of TP (Yuan et al, ). The near‐surface atmospheric water vapor isotopes plot on a line up and left of LMWL, indicating a contribution from local recycled moisture, suggesting that the common assumption ( δ A = ( δ P − ε + )/(1 + 10 −3 ε + )) is not valid for our field site.…”

“…Lakes on the southern (Shi et al, ), central (Yang et al, ), and northern (Wu et al, ) TP had different E / I ratios from this study, indicating the distinct influence of local climates and hydrological regimes in different places and the need of site‐specific research. A short‐duration lake survey (one time), such as presented in Yuan et al (), can reveal informative results of lake isotope and water balance, but detailed assessment of lake water cycle and balance relies on the continuous and long‐term lake water isotope and meteorological observations.…”

Simultaneous monitoring of stable oxygen isotope composition in water vapour and precipitation over the central Tibetan Plateau

“…Previous studies have shown that δ 18 O variations in precipitation on the southern Tibetan Plateau differ distinctly from those on the northern Tibetan Plateau (Tian et al, 2003;Yao et al, 2013). In addition, many scientists have investigated the roles of various climatic factors, especially the Asian monsoon's influence on δ 18 O in precipitation (Aizen et al, 1996;Araguás-Araguás et al, 1998;Posmentier et al, 2004;Vuille et al,ies have also investigated δ 18 O in river water (Bershaw et al, 2012), lake water (Yuan et al, 2011), and plant water Yu et al, 2014b). In comparison, only a few studies have focused on δ 18 O from water vapour over the Tibetan Plateau (Yatagai et al, 2004;Yu et al, 2005;Kurita and Yamada, 2008;Yin et al, 2008).…”

Influences of relative humidity and Indian monsoon precipitation on leaf water stable isotopes from the southeastern Tibetan Plateau

“…O and δD in water vapor [Yu et al, 2005], river water [Hren et al, 2009], and lake water [Yuan et al, 2011] have also been conducted. However, a gap exists in the studies of δ…”