A Global Perspective on Local Meteoric Water Lines: Meta‐analytic Insight Into Fundamental Controls and Practical Constraints

Abstract

Local meteoric water lines (LMWLs) represent the site‐specific long‐term covariation of hydrogen and oxygen stable isotope ratios. LMWLs have practical utility as a hydrologic framework and as benchmarks for evaluating hydroclimatic processes in isotope‐enabled climate models. In this manuscript, we characterize the global distribution of LMWLs and compare them to LMWLs from model data. To evaluate the sensitivity of the covariance of stable isotope ratios to data set length, we paired time series rarifaction with Bayesian ellipse estimation. We then applied a threshold of 48 months and estimated LMWLs at 398 sites in 25 Köppen climate classes using orthogonal distance regression. Slopes ranged from 4.8 to 10.9, with an average of 7.64 ± 0.64. Intercepts ranged from −24‰ to 27‰, with an average of 6.85 ± 6.2‰. We identified three processes: (1) subcloud evaporation of rain, (2) atmospheric remoistening by rainfall evaporation, and (3) conditions of snow formation as important controls on slopes and intercepts in arid, humid, and seasonally snowy regions, respectively. We compared observational LMWLs with those from a suite of isotope‐enabled climate models. At arid and snowy sites, model data produced higher slopes and intercepts than observational data. At humid sites, model data exhibited dampened variability in slopes and intercepts relative to observational data. These results indicate potential for improvement in the precipitation and/or isotope parameterizations of raindrop evaporation, advection of reevaporated water, evapotranspiration fractionation, and supersaturation in mixed‐phase clouds. This meta‐analysis demonstrates LMWLs utility for identifying specific hydroclimatic and isotopic processes in observations and models.

The age of surface-exposed ice along the northern margin of the Greenland Ice Sheet

“…Although this difference is small compared to global variability in that relation (e.g. Putman and others, 2019), it is consistent with previous observations of the isotopic differences between meteoric and basal ice (Larsen and others, 2010), further indicating that this layer is not meteoric.…”

Mass Balance and Climate History of a High-Altitude Glacier, Desert Andes of Chile

“…The linear relationship between δ 2 H and δ 18 O values for Guanaco is strong and without anomalous deviations (Figure 10), indicating that all precipitation events arose from well-defined and replicable meteorological processes. The high slope of the local meteoric line (8.49) and the relatively high d values (mean d = + 16.4 ± 2.3 ), as well as a positive correlation between δ 18 O and d, indicate that precipitation can include a regular contribution of re-evaporated continental surface water on a seasonal basis (Putman et al, 2019). The fact that d is always larger than 10 (corresponding to the global meteoric water line) suggests that the profile along the first 20 m of the core was not significantly affected by post-depositional sublimation processes.…”

Tracing Water Sources and Fluxes in a Dynamic Tropical Environment: From Observations to Modeling

“…Similar factors affecting leeward/windward isotopic lapse rates have been recognized in other tropical regions (Gonfiantini et al, 2001). The large sensibility of dδ/dz gradients to local circulation features, coupled with the strong seasonal and interannual bias, emphasizes the need for robust and long-term stations (>4 years; Putman et al, 2019), in particular when δ-elevation rates are used to derive critical water management information, such as mean recharge elevations (MREs), either from simple regression analysis or Bayesian methods (Yamanaka and Yamada, 2017;Sánchez-Murillo et al, 2020).…”