Ashling Neary

Bio: Ashling Neary is an academic researcher from Brown University. The author has an hindex of 1, co-authored 1 publications receiving 28 citations.

Temporal variations in lake water temperature: Paleoenvironmental implications of lake carbonate δ 18 O and temperature records

Abstract: Abstract δ 18 O and “clumped isotope” measurements of lacustrine carbonates provide important records of past terrestrial climate and paleoelevation. However, one of the primary challenges interpreting these data is constraining the relationship between mineral formation temperature and seasonal and mean annual climate. We examined surface water temperature records from 88 lakes across the globe to develop transfer functions that relate seasonal water surface temperature to mean annual air temperature. These transfer functions provide a means of reconciling proxy measures of water temperature with annual climatic conditions. Mean annual surface water temperature is related to mean annual air temperature (MAAT=−0.0318× T Water 2 +2.195× T Water −12.607; R 2 =0.96) independent of lake size, with consistently higher mean water temperatures than air. N. Hemisphere Spring (April–June) mean lake surface temperatures (MAAT=−0.0097× T Water 2 +1.379× T Water −8.227; R 2 =0.94) are only slightly warmer than MAAT for lakes in all climate zones, while summer water temperatures (JJA) (MAAT=−0.0055× T Water 2 +1.476× T Water −18.915; R 2 =0.90) may be 10–20 °C warmer than MAAT for cold climate lakes. Comparison of carbonate stable isotopic data from sites with different timescales of carbonate formation, such as found along latitude or elevation gradients, can lead to large over- or underestimates of past temperature. Accurate paleoclimatic interpretation of isotopic proxies or use of temperature proxy constraints (i.e., fossil leaves) to estimate lake temperature and calculate water δ 18 O thus requires appropriate application of water temperature–air temperature transfer functions, particularly when considering ancient cool, high elevation lake systems.

The Iso2k database: a global compilation of paleo-δ18O and δ2H records to aid understanding of Common Era climate

Abstract: Reconstructions of global hydroclimate during the Common Era (CE; the past ∼2000 years) are important for providing context for current and future global environmental change. Stable isotope ratios in water are quantitative indicators of hydroclimate on regional to global scales, and these signals are encoded in a wide range of natural geologic archives. Here we present the Iso2k database, a global compilation of previously published datasets from a variety of natural archives that record the stable oxygen (δ18O) or hydrogen (δ2H) isotopic compositions of environmental waters, which reflect hydroclimate changes over the CE. The Iso2k database contains 759 isotope records from the terrestrial and marine realms, including glacier and ground ice (210); speleothems (68); corals, sclerosponges, and mollusks (143); wood (81); lake sediments and other terrestrial sediments (e.g., loess) (158); and marine sediments (99). Individual datasets have temporal resolutions ranging from sub-annual to centennial and include chronological data where available. A fundamental feature of the database is its comprehensive metadata, which will assist both experts and nonexperts in the interpretation of each record and in data synthesis. Key metadata fields have standardized vocabularies to facilitate comparisons across diverse archives and with climate-model-simulated fields. This is the first global-scale collection of water isotope proxy records from multiple types of geological and biological archives. It is suitable for evaluating hydroclimate processes through time and space using large-scale synthesis, model–data intercomparison and (paleo)data assimilation. The Iso2k database is available for download at https://doi.org/10.25921/57j8-vs18 (Konecky and McKay, 2020) and is also accessible via the NOAA/WDS Paleo Data landing page: https://www.ncdc.noaa.gov/paleo/study/29593 (last access: 30 July 2020).

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

Abstract: Stable isotopes of oxygen (δ18O) and hydrogen (δ2H) 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 δ18O and δ2H values, modulated by lake hydrological processes, which may be functionally classified into processes that affect source water isotope values (i.e. inflow δ18O and δ2H) 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 δ18O and evaporative 18O enrichment on lake water δ18O in response to spatially variable aridity, using measurements of lake water δ2H and δ18O from 140 western Greenland lakes located between the Labrador Sea and western Greenland Ice Sheet margin. We calculated source water δ18O of lake waters (δI) using a recently developed Bayesian method and quantified evaporation-to-inflow ratios (E/I) using a modified Craig-Gordon model. δI varied by 11.1‰ across the study region, superimposed by evaporative 18O enrichment of up to 20.0‰ and E/I ranging from nearly no evaporative loss (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 δI and E/I across the study area. Substantial local variability in δI and E/I suggests catchment hydrology determines the sensitivity of δI 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.