Methane Emissions From Lakes In Northeast Siberia And Alaska Item Type Thesis Authors Walter, Katey Marion Download date 04/10/2021 10:09:08 Link to Item http://hdl.handle.net/11122/8900 METHANE EMISSIONS FROM LAKES IN NORTHEAST SIBERIA AND ALASKA A DISSERTATION Presented to the Faculty of the University of Alaska Fairbanks in Partial Fulfillment of the Requirements for the Degree of DOCTOR OF PHILOSOPHY By Katey Marion Walter, B.A., M.S. Fairbanks, Alaska May 2006 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. UMI Number: 3229744 INFORMATION TO USERS The quality of this reproduction is dependent upon the quality of the copy submitted. Broken or indistinct print, colored or poor quality illustrations and photographs, print bleed-through, substandard margins, and improper alignment can adversely affect reproduction. 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METHANE EMISSIONS FROM LAKES IN NORTHEAST SIBERIA AND ALASKA By Katey Marion Walter RECOMMENDED: Advisory Committee Cha s i a ! n ~ Assistant Chair, Department of Biology ar ildlife APPROVED: Dean, College of Natural Science and Mathematics -Cg' K ,- £ 1 1.- i - ’C t . - ■i~~~ Dean of the Graduate School / j ^-C'C L- Date Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ABSTRACT Large uncertainties in the budget of atmospheric methane (CH4), an important greenhouse gas whose relative greenhouse effect is 23 times stronger than that of carbon dioxide (CO2), limit the accuracy of climate-change projections. Concentrations of atmospheric CH4 have been rising during recent decades, particularly at high northern latitudes. The causes of this increase are not well understood. Here I describe and quantify an important source of methane—bubbling from northern lakes—that has not been incorporated in previous regional or global methane budgets. I introduce a new method to accurately measure ebullition (bubbling), which accounted for 95% of CH 4 emissions from North Siberian thaw lakes. Documenting the patchiness of ebullition increased previous estimates of CH4 flux from lakes 5-fold in Siberia and 2.5- to 14-fold in Alaska. Extrapolating estimates of measured fluxes, I show that North Siberian yedoma (Pleistocene-aged organic-rich loess) thaw lakes emit 3.8 Tg CH 4 yr'1. An independent mass-balance approach based on carbon lost from permafrost that thawed beneath lakes revealed that lakes emit 4-5 Tg CH 4 yr'1. Adding these emissions significantly increases present estimates of northern wetland contributions (<6-40 Tg yr'1) to the atmospheric CH4 budget. Thermokarst (thaw) erosion was the primary driver of CH4 emissions in lakes. A 14.7% expansion of thaw lakes from 1974 to 2000 increased lake CH4 emissions by 58% in Siberia, demonstrating a positive feedback to climate warming. The Pleistocene age of CH4 (l4C age 35,570-42,800 years in Siberia and 14,760-26,020 years in Alaska) emitted from hotspots along active thermokarst margins of lakes demonstrated that recruitment of a previously sequestered carbon source contributes to this feedback. Finally, reconstruction of yedoma’s distribution at the Last Glacial Maximum together with compilation of thaw lake basal ages that developed at the onset of Holocene warming, suggested that thaw lake development contributed up to 70% of the rapid increase in atmospheric CH4 during deglaciation. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. IV About 425 Gt C remain preserved in the yedoma ice complex in North Siberia. If this Siberian permafrost warms more rapidly in the future as projected, the positive feedback of ebullition from expanding thaw lakes could increase the rate of high-latitude warming. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. TABLE OF CONTENTS Page SIGNATURE PAGE..................................................................................................................... i TITLE PAGE................................................................................................................................. ii ABSTRACT................................................................................................................................. iii TABLE OF CONTENTS..............................................................................................................v LIST OF FIGURES................................................................................................................... viii LIST OF TABLES.........................................................................................................................x ACKNOWLEDGEMENTS....................................................................................................... xii GENERAL INTRODUCTION.................................................................................................... 1 CHAPTER 1. Methane bubbling from Siberian thaw lakes: A positive feedback to climate warming............................................................................................................................ 5 Abstract ............................................................................................................................................5 Methods..........................................................................................................................................11 Ebullition measured by bubble traps........................................................................... 11 Mapping bubble clusters in lake ice as ‘point sources ’ of ebullition..................... 12 Equations......................................................................................................................... 13 Regional extrapolation....................................................................................................14 Methane isotopes procedures....................................................................................... 14 References.....................................................................................................................................15 Figures ............................................................................................................................................ 19 Tables .............................................................................................................................................22 Supplementary Figures............................................................................................................... 23 Supplementary Tables..................................................................................................................28 CHAPTER 2. Methane bubbles in lake ice: A new method to evaluate emissions from arctic lakes.....................................................................................................................................30 Methane production and emission in northern ecosystems...................................................31 Selective sampling of bubbling points: a new technique ....................................................... 33 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. VI Application of method to other arctic and sub-arctic lakes...................................................37 Importance of point source bubbling in lakes of Alaska and Siberia ................................... 38 Implications for modeling lake bubble emissions .................................................................. 39 Hotspots of methane bubbling around the Arctic linked to thawing permafrost ................ 40 Arctic and sub-arctic lake bubbling as a source of methane to the atmosphere ................. 41 Challenge for the future ..............................................................................................................42 References....................................................................................................................................44 Figures ........................................................................................................................................... 49 Tables ............................................................................................................................................ 57 CHAPTER 3. Thaw lakes as a source of atmospheric CH4during the last deglaciation. 64 Abstract ......................................................................................................................................... 64 Notes..............................................................................................................................................71 References....................................................................................................................................