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The isotopic composition of precipitation is used to trace water cycling and climate change, but interpretations of the environmental information recorded in central Andean precipitation isotope ratios are hindered by a lack of multi‐year records, poor spatial distribution of observations, and a predominant focus on Rayleigh distillation. To better understand isotopic variability in central Andean precipitation, we present a three‐year record of semimonthly δ18Op and δ2Hp values from 15 stations in southern Peru and triple oxygen isotope data, expressed as ∆′17Op, from 32 precipitation samples. Consistent with previous work, we find that elevation correlates negatively with δ18Op and that seasonal δ18Op variations are related to upstream rainout and local convection. Spatial δ18Op variations and atmospheric back trajectories show that both eastern‐ and western‐derived air masses bring precipitation to southern Peru. Seasonal d‐excessp cycles record moisture recycling and relative humidity at remote moisture sources, and both d‐excessp and ∆′17Op clearly differentiate evaporated and non‐evaporated samples. These results begin to establish the natural range of unevaporated ∆′17Op values in the central Andes and set the foundation for future paleoclimate and paleoaltimetry studies in the region. This study highlights the hydrologic understanding that comes from a combination of δ18Op, d‐excessp, and ∆′17Op data and helps identify the evaporation, recycling, and rainout processes that drive water cycling in the central Andes. Key Points: The isotopic composition of central Andean precipitation records upstream precipitation, local convection, and remote moisture sourcesPrecipitation on the flank of the western central Andes is sourced from the Pacific Ocean∆'17O can separate evaporated and non‐evaporated samples and provides key baseline information for Andean paleoclimate and paleoaltimetry [ABSTRACT FROM AUTHOR]

Transpiration (T) is perhaps the largest fluxes of water from the land surface to the atmosphere and is susceptible to changes in climate, land use and vegetation structure. However, predictions of future transpiration fluxes vary widely and are poorly constrained. Stable water isotopes can help expand our understanding of land–atmosphere water fluxes but are limited by a lack of observations and a poor understanding of how the isotopic composition of transpired vapour (δT) varies. Here, we present isotopic data of water vapour, terrestrial water and plant water from a deciduous forest to understand how vegetation affects water budgets and land–atmosphere water fluxes. We measured subdiurnal variations of δ18OT from three tree species and used water isotopes to partition T from evapotranspiration (ET) to quantify the role of vegetation in the local water cycle. We find that δ18OT deviated from isotopic steady‐state during the day but find no species‐specific patterns. The ratio of T to ET varied from 53% to 61% and was generally invariant during the day, indicating that diurnal evaporation and transpiration fluxes respond to similar atmospheric and micrometeorological conditions at this site. Finally, we compared the isotope‐inferred ratio of T to ET with results from another ET partitioning approach that uses eddy covariance and sap flux data. We find broad midday agreement between these two partitioning techniques, in particular, the absence of a diurnal cycle, which should encourage future ecohydrological isotope studies. Isotope‐inferred estimates of transpiration can inform land surface models and improve our understanding of land–atmosphere water fluxes. [ABSTRACT FROM AUTHOR]

Forests play an integral role in the terrestrial water cycle and link exchanges of water between the land surface and the atmosphere. To examine the effects of an intermediate disturbance on forest water cycling, we compared vertical profiles of stable water vapor isotopes in two closely located forest sites in northern lower Michigan. At one site, all canopy‐dominant early successional species were stem girdled to induce mortality and accelerate senescence. At both sites, we measured the isotopic composition of atmospheric water vapor at six heights during three seasons (spring, summer, and fall) and paired vertical isotope profiles with local meteorology and sap flux. Disturbance had a substantial impact on local water cycling. The undisturbed canopy was moister, retained more transpired vapor, and at times was poorly mixed with the free atmosphere above the canopy. Differences between the disturbed and undisturbed sites were most pronounced in the summer when transpiration was high. Differences in forest structure at the two sites also led to more isotopically stratified vapor within the undisturbed canopy. Our findings suggest that intermediate disturbance may increase mixing between the surface layer and above‐canopy atmosphere and alter ecosystem‐atmosphere gas exchange. Plain Language Summary: Forests play an important role in the climate system and link water fluxes between the land surface and the atmosphere. Here we compare water vapor isotopes in two adjacent forest sites in the northern lower peninsula of Michigan to understand the effects of intermediate disturbance and canopy structure on forest water cycling. One site is dominated by aspen and birch and has a thick, closed canopy. All of the aspen and birch were killed at the second site. As a result, the disturbed site has a more open‐canopy structure. From our comparison, we found that both the species of tree and the spacing around trees are important controls on forest water cycling. With more space between trees, air mixes more freely into the canopy, which dries the forest air. Alternatively, air may be poorly mixed within and above thick, closed canopies. Key Points: Intermediate disturbance can change the contribution of entrained, evaporated, and transpired water vapor to forest canopiesCanopy gaps increase hydrologic mixing between the surface layer and the free atmosphereThe assumption of a well‐mixed canopy atmosphere may be violated in the case of thick, homogeneous forest canopies [ABSTRACT FROM AUTHOR]

The past decade has seen a remarkable expansion of studies that use mass-dependent variations of triple oxygen isotopes (16O, 17O, 18O) in isotope hydrology and isotope geochemistry. Recent technological and analytical advances demonstrate that small deviations of δ′18O and δ′17O from a mass-dependent reference relationship are systematic and are explained by well-known equilibrium and kinetic fractionations. Measurements of δ′18O and δ′17O complement traditional metrics like deuterium-excess, constrain isotope effects of kinetic fractionation that are impossible to discern with δ18O alone, and help reconstruct past environmental conditions from geologic records. In this review, we synthesize published meteoric (derived from precipitation) water triple oxygen isotope data with a new, near-global surface water dataset of δ′18O, δ′17O, δ2H, deuterium-excess, and ∆′17O, where ∆′17O is defined as δ′17O – λ ref δ′18O, δ′ notation is a logarithmic definition of the common δ value (δ′=ln(δ + 1), and λ ref is equal to 0.528. The expanded dataset shows that meteoric water δ′18O and δ′17O fit multiple regression lines and indicates that one global meteoric water line does not adequately describe all triple oxygen isotope data. Instead, this isotope system may be sensitive to processes such as moisture transport, rainout, and evaporation that do not affect the water cycle equally across the globe. This review provides a practical guide to understand ∆′17O variation in waters, explains the utility of this isotope system in hydrologic and paleoclimate studies, and outlines directions of future work that will expand the use of ∆′17O. [Display omitted] • Triple oxygen isotopes are useful in studies of hydrology and paleoclimate. • ∆′17O separates equilibrium and kinetic fractionation in the water cycle. • Water δ′18O and δ′17O data do not fit a single global meteoric water line. [ABSTRACT FROM AUTHOR]