Resolving combined influences of inflow and evaporation on western Greenland lake water isotopes to inform paleoclimate inferences

Stable isotopes of oxygen (delta O-18) and hydrogen (delta H-2) in precipitation are widely employed tracers of the global hydrologic cycle, and are frequently inferred from lake-water-derived proxies in sediments of high-latitude lakes. Lake-water isotope proxies archive precipitation delta O-18 and delta H-2 values, modulated by lake hydrological processes, which may be functionally classified into processes that affect source water isotope values (i.e. inflow delta O-18 and delta H-2) and catchment-integrated evaporation. Respectively, these controls form the basis of interpretations of precipitation isotope and effective precipitation signals from lake-water isotope proxy records. Conventionally, a single control on lake water isotope variability is assumed for a given record. Yet sensitivity to these controls depends on regional hydroclimate and local hydrology, which may change through time. We quantified the relative impacts of variations in inflow delta O-18 and evaporative O-18 enrichment on lake water delta O-18 in response to spatially variable aridity, using measurements of lake water delta H-2 and delta O-18 from 140 western Greenland lakes located between the Labrador Sea and western Greenland Ice Sheet margin. We calculated source water delta O-18 of lake waters (delta I) using a recently developed Bayesian method and quantified evaporation-to-inflow ratios (E/I) using a modified Craig-Gordon model. delta I varied by 11.1 parts per thousand across the study region, superimposed by evaporative O-18 enrichment of up to 20.0 parts per thousand and E/I ranging from nearly no evaporative loss (E/I < 0.10) to desiccation (E/I > 1). Lakes can be broadly classified as predominantly sensitive to inflow or evaporation, corresponding to their location along the aridity gradient, and there are significant trends in both delta I and E/I across the study area. Substantial local variability in delta I and E/I suggests catchment hydrology determines the sensitivity of delta I and E/I to changes in aridity, and implies that hydrological end-member lakes within a small region may provide complementary records of seasonal precipitation isotope values and ice-free-season evaporation. Deconvolving modern controls on lake water isotope values provides essential support for quantitative and seasonal paleoclimate inferences from paleolimnological isotope data, which will improve constraints on the long-term variability of the Arctic hydrologic cycle.