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Antarctic Climate of the Past 200 Years from an Integration of Instrumental, Satellite, and Ice Core Proxy Data

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Antarctic Climate of the Past 200 Years from an Integration of Instrumental, Satellite, and Ice Core Proxy Data Antarctic climate of the past 200 years from an integration of instrumental, satellite, and ice core proxy data David P. Schneider A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy University of Washington 2005 Program Authorized to Offer Degree: Department of Earth and Space Sciences University of Washington Graduate School This is to certify that I have examined this copy of a doctoral dissertation by David P. Schneider and have found that it is complete and satisfactory in all respects, and that any and all revisions required by the final examining committee have been made. Chair of Supervisory Committee: ___________________________________________________________ Eric J. Steig Reading Committee: ___________________________________________________________ Eric J. Steig ___________________________________________________________ Stephen G. Warren ___________________________________________________________ John M. Wallace Date: ________________________________ In presenting this dissertation in partial fulfillment of the requirements for the doctoral degree at the University of Washington, I agree that the Library shall make its copies freely available for inspection. I further agree that extensive copying of the dissertation is allowable only for scholarly purposes, consistent with “fair use” as prescribed in the U.S. Copyright Law. Requests for copying or reproduction of this dissertation may be referred to Proquest Information and Learning, 300 North Zeeb Road, Ann Arbor, MI 48106-1346, or to the author. Signature __________________________ Date _____________ University of Washington Abstract Antarctic climate of the past 200 years from an integration of instrumental, satellite, and ice core proxy data David P. Schneider Chair of the Supervisory Committee: Associate Professor Eric J. Steig Department of Earth and Space Sciences Ice core records are the only direct means of extending Antarctic climate records into the past, before observations began in the late 1950s. Before proxy records are used with confidence, their relationship to climate parameters of interest (e.g. temperature, geopotential height, precipitation) must be clearly demonstrated. I assess the dominant patterns of variance in climate parameters over the Antarctic through an analysis of passive microwave and thermal infrared data from instruments on polar-orbiting satellites. Differences between the two data sets are largely due to near-surface snow properties. The most important mode of the Southern Hemisphere (SH) atmospheric circulation, the Southern Annular Mode (SAM), is associated with the leading empirical orthogonal functions of the satellite temperature data sets. Stable isotope ratios of water (δD and δ18O) were measured in nearly two dozen, sub-annually resolved, ~200-year-long ice cores that were obtained during traverses across West Antarctica. I use data from twelve of the cores in a compositing analysis to asses whether atmospheric modes have an expression in the isotopic composition of the firn. The SAM has a distinct spatial expression in δ; δ anomalies have the same sign as temperature anomalies at several of the sites. All of the δ records strongly correlate with the seasonal cycle of temperature. However, neither the coefficients from the seasonal regressions nor the compositing analysis are reliable as a calibration for reconstruction of temperature. I show that an important target for ice core calibrations is the average of the annual mean temperature records from Antarctic weather stations. This index has a strong correlation with the first mode of the infrared temperature data. Stacked ice core records have good skill in explaining its variance. A 200-year reconstruction of this index is presented, based on scaling a stack of five ice core records. During the period of overlap (1856-1999) with the observed SH mean temperature record, the reconstruction suggests that Antarctic temperatures (excluding the Peninsula) have had a relatively stable mean, though have slightly increased, at about half the rate of the SH mean. Deviation of Antarctic temperature trends from the SH warming can in part be explained by the positive trend in the SAM since the mid-1970s. TABLE OF CONTENTS Page List of Figures..............................................................................................................................ii List of Tables ..............................................................................................................................iii Introduction.................................................................................................................................. 1 Chapter 1: Recent climate variability in Antarctica from satellite-derived temperature data..... 7 Chapter 2: New high-resolution ice cores from Antarctica: Sites, climatology, and stable isotope measurements ................................................................................................................ 37 Chapter 3: High resolution ice core stable isotopic records from Antarctica: Towards interannual climate reconstruction............................................................................................. 52 Chapter 4: Ice core evidence for Antarctic climate change ...................................................... 73 Chapter 5: Spatial covariance of isotopic signals in West Antarctica .................................... 103 Chapter 6: Conclusions and future outlook............................................................................. 128 Bibliography ............................................................................................................................ 131 i LIST OF FIGURES Figure Number Page 1.1 Results from PCA of monthly 1982-1999 TIR anomaly data.............................................. 28 1.2 Mean microwave emissivity estimates ............................................................................... 29 1.3 Heterogeneous regression maps from MCA of TIR and TB fields....................................... 30 1.4 Expansion coefficients of the first three MCA modes........................................................ 31 1.5 Power spectra of the MCA expansion coefficients............................................................. 32 1.6 The leading modes in monthly 500-hPa geopotential height.............................................. 33 1.7 Regressions of TIR gridpoint data upon the first three Z500 normalized PCs..................... 34 1.8 Regression of 1982-1999 monthly Z500 data upon the SOI............................................... 35 1.9 Regression of Z500 data upon the TIR expansion coefficients........................................... 36 2.1 Maps of mean annual temperature...................................................................................... 45 2.2 Map of mean annual accumulation rate .............................................................................. 46 2.3 Map of US-ITASE traverse routes...................................................................................... 47 2.4 Section of δ18O data from core 2001-5 ............................................................................... 48 2.5 Mean values of δ18O versus elevation and temperature ..................................................... 49 2.6 Mean annual temperature versus elevation at selected ice core sites.................................. 50 2.7 Time series of δ18O and δD from seven US-ITASE cores.................................................. 51 3.1 Map indicating selected ice core and weather station sites................................................. 70 3.2 Annual cycle of surface temperature and isotopic values at several sites........................... 71 3.3 Estimates of annually averaged Antarctic temperature anomalies from weather stations and ice core proxies ................................................................................................................... 72 4.1 Map indicating selected ice core and weather station sites................................................. 93 4.2 Antarctic surface temperature anomalies and the SAM index............................................ 94 4.3 Antarctic temperature reconstruction over the past 200 years ............................................ 95 4.4.S1. Spatial representativeness of the A8 target index ........................................................ 96 4.5.S2. Seasonal indices of Antarctic temperature compared with the SAM .......................... 97 4.6.S3. The annual mean ice core δ time series used in the reconstruction .............................. 98 4.7.S4. Reconstructions based on five-year averages ............................................................... 99 5.1 Regression patterns in annual 500-hPa geopotential height anomalies. ........................... 124 5.2 Isotope data versus depth, core US-ITASE 2000-3 .......................................................... 125 5.3 Oxygen isotope data from core US-ITASE 2000-2 .......................................................... 126 5.4 Percent of total monthly variance explained by anomalies of TIR .................................... 127 ii LIST OF TABLES Table Name and Number Page 1.1 Variance explained by the first two EOFS and the correlation with the SAM index by season......................................................................................................................................... 24 1.2
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