ABSTRACT HOLOCENE AND TERMINAL PLEISTOCENE CLIMATE IN THE PACIFIC NORTHWEST: A POLLEN RECORD FROM LAKE LOUISE, WASHINGTON Pollen extracted from lake sediments provides the ability to reconstruct Holocene vegetation history, providing a proxy for changes in temperature, precipitation and fire- or erosion-related disturbance at Lake Louise, near the southern terminus of Puget Sound, Washington State, USA. The resulting assemblage is divided into four zones. Z4, the oldest of these, and dominated by Pinus, suggests a cold climate. Z3 exhibits an increase in Pseudotsuga menziesii and Alnus rubra, indicating warmer conditions and increased disturbance, likely due to increased fire frequency. In Z2, Thuja and Tsuga increase, as Alnus declines, and Pseudotsuga declines slightly. This suggests higher precipitation, slightly cooler conditions, and decreased disturbance. Finally, Z1 shows an increase in Alnus, a slight increase in Pseudotsuga, no change in Tsuga, and a decrease in Thuja, signaling slightly increased temperatures, with increased disturbance, and consistent high precipitation. The general trends detected are similar to others observed in similar studies across the region. Jeremy Matthew Scherr August 2015 HOLOCENE AND TERMINAL PLEISTOCENE CLIMATE IN THE PACIFIC NORTHWEST: A POLLEN RECORD FROM LAKE LOUISE, WASHINGTON by Jeremy Matthew Scherr A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science in Geology in the College of Science and Mathematics California State University, Fresno August 2015 APPROVED For the Department of Earth and Environmental Sciences: We, the undersigned, certify that the thesis of the following student meets the required standards of scholarship, format, and style of the university and the student's graduate degree program for the awarding of the master's degree. Jeremy Matthew Scherr Thesis Author Peter Van de Water (Chair) Earth and Environmental Sciences Mathieu Richaud Earth and Environmental Sciences Robert Dundas Earth and Environmental Sciences For the University Graduate Committee: Dean, Division of Graduate Studies AUTHORIZATION FOR REPRODUCTION OF MASTER’S THESIS X I grant permission for the reproduction of this thesis in part or in its entirety without further authorization from me, on the condition that the person or agency requesting reproduction absorbs the cost and provides proper acknowledgment of authorship. Permission to reproduce this thesis in part or in its entirety must be obtained from me. Signature of thesis author: ACKNOWLEDGMENTS I would like to thank my advisor, Professor Peter Van de Water, for approximately 99 instances of assistance through every step along the way. Without his patience, insight, and clarity, this work would not have been possible. I would like to thank my committee members, Professors Mathieu Richaud and Robert Dundas. Through their diligence, this paper has gone from unremarkable raw stone, through cutting and polishing, to achieve its full potential. Thanks to Kena Fox-Dobbs, Jeff Tepper and their students, for their work in acquisition of the core itself, and for other forms of analysis that add significantly to overall understanding of the Lake Louise record. Finally, thanks to Judy Stone, Mary Phillips, Emily Michel, and all of the friends I have made in the EES department of CSU Fresno, for all the support that they have given me in this undertaking. TABLE OF CONTENTS Page LIST OF TABLES .................................................................................................. vi LIST OF FIGURES .................................................................................................. 1 INTRODUCTION .................................................................................................... 1 LITERATURE REVIEW ......................................................................................... 5 Overview ........................................................................................................... 5 Puget Coastal Rain Shadow .............................................................................. 7 Southern Puget Lowland ................................................................................. 10 Olympic Peninsula West Coast ....................................................................... 11 Surrounding Areas .......................................................................................... 13 METHODS ............................................................................................................. 15 RESULTS ............................................................................................................... 18 DISCUSSION ......................................................................................................... 22 Overview ......................................................................................................... 22 Terminal Pleistocene and Early Holocene ...................................................... 23 Middle Holocene ............................................................................................. 27 Late Holocene ................................................................................................. 28 WORKS CITED ..................................................................................................... 30 APPENDIX: POLLEN SITES OF THE PACIFIC NORTHWEST ...................... 36 LIST OF TABLES Page Table 1. Pollen Sites From Previous Research in Region Surrounding Lake Louise ......................................................................................................... 7 LIST OF FIGURES Page Figure 1. View of western Washington state, with previous pollen research sites from literature review shown. ........................................................... 2 Figure 2. Approximate location of the Lake Louise sediment core sample, USGS 7.5" Steilacoom topographic quadrangle. ...................................... 4 Figure 3. Lake Louise pollen percentage diagram showing percentage abundance of conifer and other arboreal taxa, plotted against core depth. ....................................................................................................... 19 Figure 4. Lake Louise pollen percentage diagram showing non-arboreal, aquatic and other pollen, as well as abundance summation and lycopodium to pollen ratio, plotted against depth. ................................. 20 Figure 5. Ternary diagram showing covariance, with end members Pinus (cold) Pseudotsuga (warm) and Thuja (wet). ......................................... 23 INTRODUCTION The Pleistocene-Holocene boundary marks the transition from glacial conditions, and the rise of our current interglacial environment (Walker et al., 2009). Within this interglacial, climate has fluctuated to varying degrees (Mayewski et al., 2004). These shifts affect our ecosystems and thus result in changes to the floral assemblage in a given region over time. By examining pollen extracted from sediment, the history of changes in a floral assemblage can determine, with sufficient precision to be useful, a proxy for changes in the regional climate. The nature of such changes can be further constrained by examining charcoal extracted from sediment. During the terminal Pleistocene, the glacial terminus of the western Cordilleran glacial ice mass occurred in western Washington state (Figure 1). The region thereby provides key insights in understanding Holocene climate (Tsukada et al., 1981). The southern terminus of the Continental ice sheet in the Puget lowlands has borne comparably little scrutiny of the available pollen sites. The Puget Trough is a low elevation region, whose northern interface sinks below current sea level and coincides with that of Puget Sound. The trough extends southward through Washington (Barnosky, 1985) and northern Oregon, at which point it becomes the Willamette Valley. It is bounded on the west by the coastal ranges, and on the east by the Cascades (Barnosky, 1985). The northern extent of the region was predominantly physiographically influenced by the Puget Lobe of the Cordilleran ice sheet during the Vashon stade of the Fraser Glaciation (Hibbert, 1979). The formation of the Puget Sound occurred as the Cordilleran ice sheet retreated. Based on a time-distance curve of glacial advance and retreat, supported by radiocarbon dating of specific sites (Porter and Swanson, 1998), the region currently occupied by Lake Louise would have been free of ice around 16.6 ka. 2 2 Figure 1. View of western Washington state, with previous pollen research sites from literature review shown. Note: Lake Louise is represented by LL. For the key to other sites, see Appendix. 3 3 Regional climate west of the Cascade mountains alternates between dry summers and wet winters. The Puget Trough, located in a partial rain shadow caused by the Olympic Mountains to its west, experiences reduced precipitation compared to the coastal region. Precipitation also increases significantly to the east as elevation rises in the Cascades. Lake Louise, a circular depression of 0.16 km2 of surface area, is interpreted as a kettle lake, with maximum depth of 10.7 m (Wolcott, 1961). It is located approximately 3.2 km east of the nearest extension of Puget Sound and the town of Steilacoom, Washington (Figures 1, 2). The deepest sediments represent the lake in its infancy, in a basin exposed, and then filled with melt-water from recently retreated glaciers, as the Vashon stade gave way to the present