1,721,117 research outputs found
High resolution stable isotopes of ice core Taylor Dome to 230 kyr
No full textThe delta 18O values were determined at the Quaternary Isotope Laboratory (M. Stuiver, Box 351360, University of Washington, Seattle WA 98195, USA). The time scale (st9810) is a combined timescale from geophysical measurements, gas-correation with the GISP2 layer-counted chronology (central Greenland), and interpolation using gas and 10-Be control points. Details are given in Steig et al., 2000. All of the data in this file are from samples bottled at the University of New Hampshire. Samples are "residue" from the UNH automated melting system, used as a prep. system for ion chromatography measurements. All ice was sampled at the NationalIce Core Laboratory
Age model and delta deuterium of ice core Taylor Dome from 20 to 10 kyr
No full textTwo timescales are reported here. The original is as reported in Steig et al., Science 282 (1998). This was adjusted slightly to match the flow-model constrained st9810 timescale (Steig et al., Geografiska Annaler, 2000). The adjustment is well within the uncertainties of the timescale and is more the sake of convenience. In general, the st9810 timescale should be used
Investigating the drivers of glacier retreat in West Antarctica using proxy-data assimilation and numerical modeling
No full textThesis (Ph.D.)--University of Washington, 2023Outlet glaciers in West Antarctica are rapidly retreating and contributing to sea level rise. Ice loss is primarily occurring via wind-driven incursions of warm circumpolar deep water melting the ice shelves that buttress the glaciers. The leading hypothesis is that the current stage of retreat was triggered by a wind-driven change in ocean conditions that occurred in the mid-20th century. However, the short record of observed wind and ocean conditions in this region leaves our knowledge of the mechanisms driving glacier retreat highly uncertain (i.e., what wind/ocean changes occurred, and whether they are characteristic of natural variability or a response to anthropogenic forcing). Here, I use proxy data to reconstruct atmospheric circulation around Antarctica over the full 20th century, revealing century-scale trends and a large westerly event in the 1940s; both are candidates for initiating the current stage of retreat. I investigate the potential for the 1940s westerly event to induce substantial changes in ocean conditions near West Antarctica by using numerical modeling to constrain the sensitivity of ocean circulation to various local wind events. I find evidence that: (1) the circumpolar westerly winds have strengthened over the 20th century, in a zonally asymmetric pattern with the strongest wind trends occurring in the mid-latitude Pacific at approximately 55°S; (2) an unusually large and persistent westerly event occurred near West Antarctica from approximately 1938 to 1942, coinciding with the estimated start of glacier retreat. The results from my numerical ocean modeling experiments show that 5-year wind events with a similar pattern are indeed capable of enhancing the transport of warm circumpolar deep water toward the glaciers, but that the ocean is highly sensitive to the pattern of local wind forcing. The studies in this dissertation demonstrate that using nontraditional data sources from proxy records can provide novel constraints and useful insight on the complex atmosphere-ocean-ice processes occurring in this region. The results reveal several unexpected nuances to relationships widely accepted by the scientific community and highlight several specific lines of research that can further advance our understanding of the historical drivers of glacier retreat in West Antarctica
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Low resolution stable isotopes of ice core Taylor Dome
No full textThe delta 18O values were determined at the Quaternary Isotope Laboratory (M. Stuiver, Box 351360, University of Washington, Seattle WA 98195, USA). The time scale (st9507) was estimated from a correlation of delta 18O with the Vostok delta D record (Grootes et al. 1994; Steig, 1996). Between 0-340m the samples measured were of 1m cuts taken in the field. Each 1m core section was slabbed to provide a surface for ECM measurement; a thin slice was removed uniformly along the length for isotope analysis. From 340m to the bottom, sampling was done at the National Ice Core Lab at 0.5m lengths. Note that these core sections were shipped intact to NICL; they were not processed in the field
Fundamental controls on triple oxygen-isotope ratios in Antarctic precipitation and ice cores
Get PDFThesis (Ph.D.)--University of Washington, 2015Stable isotope ratios of water (δD and δ18O) in polar precipitation and ice cores have long been used to study past climate variations and the hydrological cycle. Recently-developed methods permit the precise measurement of δ17O and the 17O-excess, relative to the δ17O vs. δ18O meteoric water line. The novel isotope parameter "17Oexcess" provides an additional tool for investigating the global hydrological cycle. Early experimental and modeling studies showed that 17Oexcess in atmospheric water vapor is sensitive to relative humidity during evaporation from the ocean surface, and suggested that there was little fractionation during condensation. It was therefore expected that 17Oexcess in polar snow could be used as an indicator for humidity in the ocean source regions where polar moisture originates. Later work shows that the magnitude of 17Oexcess change between the last glacial period and the Holocene warm period, measured in Antarctic ice cores, increases from the Antarctic coast towards the interior, suggested significant fractionation during transport. Full interpretation of these conflicting results has been challenging, hindered in part by the labor-intensive nature of making 17Oexcess measurements and by the lack of an accepted standard for reporting 17Oexcess values. This thesis provides a new, comprehensive assessment of the 17Oexcess of Antarctic precipitation and ice core data. The contributions from this work also include improvements to 17Oexcess measurement techniques, using both isotope-ratio mass spectrometry and collaborative developments in laser spectroscopy, and a formal calibration of international water standards for 17Oexcess. It further addresses both the spatial and temporal variations observed in Antarctic 17Oexcess values, providing a coherent explanation for both. New Antarctic 17Oexcess measurements from this work show that there is a strong negative spatial gradient of 17Oexcess in snowfall towards the interior of Antarctica, a similar spatial pattern to the glacial-interglacial change in 17Oexcess, and a smaller-amplitude seasonal cycle in West Antarctica than in the interior of East Antarctica. These measurements, when combined with earlier published work, provide the most complete view of the spatial distribution and temporal variability of 17Oexcess to date. Model studies, using both an intermediate complexity isotope model (ICM) and an isotope-enabled general circulation model (GCM), have permitted a thorough investigation of the most relevant and important processes affecting 17Oexcess in Antarctica. The model simulations show that changes in source relative humidity have only a modest effect on 17Oexcess in polar precipitation, and can not account for the full seasonal cycle amplitude, nor the large glacial-interglacial 17Oexcess changes observed in Antarctic ice cores. The spatial gradient of 17Oexcess in modern precipitation, along with the large amplitude seasonal cycle in East Antarctica and the greater magnitude of 17Oexcess change for interior sites between glacial and interglacial periods, can be explained by kinetic isotope fractionation during snow formation under supersaturated conditions. The model experiments further show that the influence of moisture recharge is important to the evolution of 17Oexcess in poleward-moving air masses. The seasonal presence of sea ice is also a significant factor affecting 17Oexcess. Greater sea ice concentration or extent reduces evaporative recharge and increases the spatial area over which kinetic fractionation processes are important; both these factors tend to lower 17Oexcess
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Developing water-isotope records from stratigraphically disturbed blue ice: observations, limitations, and insights from the Allan Hills of Antarctica
No full textThesis (Ph.D.)--University of Washington, 2025Polar ice cores contain direct archives of past atmosphere and past precipitation, and water-isotope measurements of polar ice-core samples are used to reconstruct Earth's past climate. Ice cores from stable domes or ice divides -- where post-depositional ice flow results primarily from compression of more recently accumulated snowfall -- have produced continuous climate records as old as 800 ka. Climate records from older ice cores are of interest due to a notable change in Earth's climatic fluctuations around 1 Ma. Extending the ice-core paleoclimate record beyond 1 Ma likely requires measurements from more complicated depositional environments, such as from blue ice areas at the margins at the Antarctic ice sheet. The Allan Hills blue-ice area contains ice as old as 6 Ma at relatively shallow depths (<200 m below the surface), but cores from this region are typically discontinuous and stratigraphically disturbed. In addition, they have likely experienced orders of magnitude more thinning than more typical ice cores, severely limiting their temporal resolution. The development and interpretation of ice-core climate records from blue-ice areas is still in nascent stages, and is only possible due to the development of an absolute dating technique by the analysis of atmospheric 40-Ar (Bender et al., 2008). Age constraints at discrete depths along the core provide information about the average age of the ice, but significant uncertainty remains about the amount of time represented by each measurement. Here, I present new water-isotope records from discontinuous blue-ice cores from the Allan Hills blue ice area of Antarctica, and explore the implications and limitations of those data. This thesis uses high-resolution water-isotope data to explore the integrated history of ice recovered from the Allan Hills. It (1) details advancements in high-resolution water-isotope measurement methodology by continuous-flow analysis, which is the preferred method for analyzing many Allan Hills cores, (2) advances our understanding of water-isotope signal preservation and alteration in blue ice by examining the reproducibility of the water-isotope record at lateral distances of 0.22 to 140 m, (3) demonstrates that glacial-interglacial signals are preserved in some disturbed Allan Hills ice and provides insights into ice accumulation and climate history in this area, and (4) explores differences in water-isotope distillation pathways caused by atmosphere and ocean changes between the present-day and a warmer (i.e. 6-Ma) world
Climate dynamics revealed in ice cores: advances in techniques, theory, and interpretation
No full textThesis (Ph.D.)--University of Washington, 2017-08Ice cores from the polar ice sheets provide detailed histories of Earth's climate. Interpreting past climate dynamics from ice-core records requires understanding how the climate system influences the geochemical proxies preserved in the ice. Models of physical climate processes have always formed the basis of climate-proxy interpretations. In this thesis I investigate how atmospheric transport of moisture toward the poles influences the water-isotope ratios of Antarctic precipitation as well as the amount of aerosols that reach the ice sheets. I refine interpretations of these geochemical proxies and the relationships between them. These interpretations help us better understand past climate dynamics, including changes in mid- and high-latitude temperatures and changes in the patterns of atmospheric circulation in the Southern Hemisphere. I make use of new high-resolution proxy records from a West Antarctic ice core and use both simple and complex physical models to better understand the relationships between the climate, moisture transport, and the geochemical proxies. This work improves our understanding of the spatial pattern and timing of climate changes in the Southern Hemisphere over the last 70,000 years
- …
