Late Holocene climate and glacier fluctuations in the Cambria Icefield area, British Columbia Coast Mountains.




Johnson, Kate

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In the British Columbia Coast Mountains most dendroclimatological and dendroglaciological studies have focused on developing insights from tree‐ring sites located in the southern and central regions. By contrast relatively few studies have been conducted in the northwestern Coast Mountains, where exploratory studies reveal that significant climate‐radial growth relationships exist. The purpose of this study was to develop a proxy record of climate change from tree rings and to reconstruct the late Holocene glacial history of two outlet glaciers spilling eastward from th e Cambria Icefield. Dendroclimate investigations were conducted using mountain hemlock (Tsuga mertensiana) trees growing on three high‐elevation montane slopes. The three stands located along a 35 km transect cross date to form a master chronology for the region spanning 409 years (1596 to 2007 A.D.). Correlation analyses show that the radial growth of the regional tree‐ring chronology corresponds to variations in the mean June‐July‐August (JJA) air temperature. The relationship between the two variables was used to reconstruct mean JJA air temperature from 1680 to 2007 A.D.). The reconstruction illustrates warm and cool intervals that are synchronous ito those derived from other paleoenvironmental research in this region. The proxy record also highlights annual to inter‐decadal climate variability likely resulting from atmospheric‐ocean circulation patterns described by the El Niño‐Southern Oscillat ion and the Pacific Decadal Oscillation. The late Holocene behaviour of White and South Flat glaciers was investigated using radiocarbon dating techniques, dendrochronological cross‐dating techniques and geomorphological analysis of sedimentary units within the White and South Flat glacier forefields. Evidence for a First Millennial Advance (FMA) cumulating around 650 A.D. and early Little Ice Age (LIA) advances at 1200 and 1400 A.D. were documented. These advances are contemporaneous with the late Holocene activity of glaciers throughout the region, suggesting coherent broad‐scale climate forcing mechanisms have influence glacial mass balance regimes over at least the last two millennia. The dendroclimatological and dendroglaciological findings of the study provide the first annually‐resolved climate record for the region and help to enhance our understanding of late‐Holocene glacier behaviour in the Cambria Icefield Area. The thesis documents the complex interactions between climate and the radial growth of mountain hemlock trees in the Pacific Northwest, and describes the role that long‐term climate variability played in glacier dynamics during the FMA and LIA.



Coast Mountains (B.C. and Alaska), glaciers