Sensitivity and Response of Bhutanese Glaciers to Atmospheric Warming

Glacierized change in the Himalayas affects river-discharge, hydro-energy and agricultural production, and Glacial Lake Outburst Flood potential, but its quantification and extent of impacts remains highly uncertain. Here we present conservative, comprehensive and quantitative predictions for glacier area and meltwater flux changes in Bhutan, monsoonal Himalayas. In particular, we quantify the uncertainties associated with the glacier area and meltwater flux changes due to uncertainty in climate data, a critical problem for much of High Asia. Based on a suite of gridded climate data and a robust glacier melt model, our results show that glacier area and meltwater change projections can vary by an order of magnitude for different climate datasets. However, the most conservative results indicate that, even if climate were to remain at the present-day mean values, almost 10% of Bhutan s glacierized area would vanish and the meltwater flux would drop by as much as 30%. Under the conservative scenario of an additional 1 C regional warming, glacier retreat is going to continue until about 25% of Bhutan s glacierized area will have disappeared and the annual meltwater flux, after an initial spike, would drop by as much as 65%. Citatio

A window into terrestrial paleoclimate: soil carbonate formation processes and climate proxy applications

Thesis (Ph.D.)--University of Washington, 2018The isotopic composition of pedogenic (formed in soil) carbonates provides a geologically abundant archive of terrestrial climate change and the interactions between Earth’s climate, geologic, and biologic systems. However, early paleoclimate reconstructions based on the carbon and oxygen isotope composition of soil carbonates were largely limited to qualitative estimates of change in key climate and environmental parameters such as surface temperature, precipitation, and soil biologic activity. The development of carbonate clumped isotope geothermometry has made it possible to make quantitative estimates of carbonate formation temperatures, and to relate those temperatures to changes in the Earth’s climate. The application of carbonate clumped isotope geothermometry to studies of soil carbonate systematics has shown that the seasonality of soil carbonate formation is closely linked to the timing of the local wet season, which has important implications for how the clumped isotope formation temperatures of soil carbonates relate to more meaningful climatologic parameters such as mean annual temperature. However, important questions remain regarding the impact of other climate and soil factors such as precipitation type (e.g., rain versus snow) and soil sediment grain size on the seasonality and mechanisms of soil carbonate formation. This dissertation places new constraints on the effects these soil and climate factors have on the seasonality of soil carbonate formation, sheds new light on non-equilibrium formation processes affecting soil carbonates in freezing environments, and provides new, quantitative terrestrial paleoclimate reconstructions of seasonal variability in surface temperature during the Late Cretaceous greenhouse period. Chapter 2 presents soil carbonate clumped and stable isotope data from an approximately 4000 m elevation transect on the western flank of the Chilean Andes. The results from this first chapter provide evidence that the presence or absence of a winter snowpack plays a critical role in modulating soil wetting and drying cycles, which in turn dictate the seasonality of soil carbonate formation. Additionally, this work provides the first evidence of soil carbonate formation under conditions of isotopic disequilibrium in freezing environments. Chapter 3 builds on the results of Chapter 2 by presenting the analyses of a suite of cold-climate soil carbonates from soils with both fine grained (the High Arctic and the Tibetan Plateau) and coarse grained (the Chilean and Argentinian Andes and the Dry Valleys, Antarctica) inter-cobble matrices. The findings of this chapter show that in freezing soils, matrix grain size is an important control on promoting or inhibiting kinetic isotope effects during soil carbonate formation. Soils with coarse-grained matrices experience rapid CO2 degassing associated with bicarbonate dehydration during soil freezing, which results in disequilibrium soil carbonate formation. In contrast, fine-grained matrices inhibit soil CO2 degassing and promote equilibrium carbonate formation, even in freezing environments. Chapter 4 represents and application of cutting-edge soil carbonate paleoclimate reconstruction techniques to the long-standing issue of terrestrial seasonal temperature variability during greenhouse climates. The clumped isotope composition of paleosol carbonates from Late Cretaceous sedimentary outcrops in south-central Utah and northwest Montana, USA are used to reconstruct summer soil temperatures along the mid-latitude, western margin of the Western Interior Seaway. These summer temperatures are then paired with previous reconstructions of local mean annual temperature to reconstruct mean annual range in temperature for these two sites. The results of this work show better agreement with model simulations of Late Cretaceous seasonal temperature changes than previous estimates, and add to a growing body of work that suggests that seasonal temperature variations in greenhouse environments did not differ significantly from the modern. These findings have important implications not only for our understanding of greenhouse climate, but also for the impact of climate on the paleogeographic distribution of ancient faunal communities

Water stable isotope record of ice core WAIS divide

Changes in atmospheric circulation over the past five decades have enhanced the wind-driven inflow of warm ocean water onto the Antarctic continental shelf, where it melts ice shelves from below. Atmospheric circulation changes have also caused rapid warming over the West Antarctic Ice Sheet, and contributed to declining sea-ice cover in the adjacent Amundsen-Bellingshausen seas. It is unknown whether these changes are part of a longer-term trend. Here, we use water-isotope (d18O) data from an array of ice-core records to place recent West Antarctic climate changes in the context of the past two millennia. We find that the d18O of West Antarctic precipitation has increased significantly in the past 50 years, in parallel with the trend in temperature, and was probably more elevated during the 1990s than at any other time during the past 200 years. However, d18O anomalies comparable to those of recent decades occur about 1% of the time over the past 2,000 years. General circulation model simulations suggest that recent trends in d18O and climate in West Antarctica cannot be distinguished from decadal variability that originates in the tropics. We conclude that the uncertain trajectory of tropical climate variability represents a significant source of uncertainty in projections of West Antarctic climate and ice-sheet change

Recent climate and ice-sheet changes in West Antarctica compared with the past 2,000 years

International audienc

InterCarb: A Community Effort to Improve Interlaboratory Standardization of the Carbonate Clumped Isotope Thermometer Using Carbonate Standards

International audienceIncreased use and improved methodology of carbonate clumped isotope thermometry has greatly enhanced our ability to interrogate a suite of Earth-system processes. However, interlaboratory discrepancies in quantifying carbonate clumped isotope (Δ47) measurements persist, and their specific sources remain unclear. To address interlaboratory differences, we first provide consensus values from the clumped isotope community for four carbonate standards relative to heated and equilibrated gases with 1,819 individual analyses from 10 laboratories. Then we analyzed the four carbonate standards along with three additional standards, spanning a broad range of δ47 and Δ47 values, for a total of 5,329 analyses on 25 individual mass spectrometers from 22 different laboratories. Treating three of the materials as known standards and the other four as unknowns, we find that the use of carbonate reference materials is a robust method for standardization that yields interlaboratory discrepancies entirely consistent with intralaboratory analytical uncertainties. Carbonate reference materials, along with measurement and data processing practices described herein, provide the carbonate clumped isotope community with a robust approach to achieve interlaboratory agreement as we continue to use and improve this powerful geochemical tool. We propose that carbonate clumped isotope data normalized to the carbonate reference materials described in this publication should be reported as Δ47 (I-CDES) values for Intercarb-Carbon Dioxide Equilibrium Scale