It has become increasingly clear that climate fluctuations during the Holocene
interval were unusually frequent and rapid, and that our current understanding of the
temporal and spatial distribution of these oscillations is incomplete. Little
paleoenvironmental research has been undertaken on the windward side of the central Coast Mountains of British Columbia, Canada. Very high annual orographic precipitation totals, moderate annual temperatures regulated by the Pacific Ocean, and extreme topographic features result in a complex suite of microclimate conditions in this largely unstudied area.
Dendroclimatological investigations conducted on a steep south-facing slope near
Confederation and Franklin glaciers suggest that both mountain hemlock (Tsuga
mertensiana) and subalpine fir (Abies lasiocarpa) trees at the site are limited by previous year mean and maximum summer temperatures. A regional subalpine fir chronology for the central and southern Coast Mountains indicates that subalpine fir trees at the study site experience physiological stress with warm summer temperatures, despite the high
annual precipitation totals experienced there. This response is likely a result of the extreme gradient and the aspect of the slope at the sampling location, underscoring the importance of site characteristics on annual radial tree growth. Local (AD 1820-2008) and regional (AD 1700-2008) tree ring width chronologies were used to reconstruct
previous July mean and maximum temperatures, explaining between 13% and 36% of the
variance in climate. The proxy record features cool intervals that are comparable to other paleoenvironmental research from the region, and cyclical oscillations in temperature commonly associated with the El Niño Southern Oscillation and Pacific Decadal
Oscillation. Century-scale fluctuations may be connected to changes in solar irradiance.
Dendroglaciological investigations were undertaken at the confluence of the
Confederation and Franklin glaciers with the intention of exploring the Holocene
behaviour of low-elevation maritime glaciers in this region. These glaciers are suspected
to be sensitive to variations in the mean position of winter freezing level heights and
warm winter temperatures, and may respond differently to changes in climate than more
continental glaciers. Buried wood samples were radiocarbon-dated and cross-dated to
construct three floating chronologies. Float A (r = 0.467) suggests an early Little Ice Age advance of the two glaciers, and Float B (r = 0.466) suggests an early Tiedemann
advance of Confederation Glacier. Float C (r = 0.519) is dated to the Garibaldi Phase of
glacier expansion, but may not have been killed by glacial activity. The temporal
synchronicity of these findings with glacial events documented throughout the region
suggests a spatially coherent response of maritime and continental glaciers to the
dominant climate–forcing mechanisms operating in Pacific North America throughout
the late Holocene.
The dendroclimatological and dendroglaciological findings of this study help to fill a spatial research gap in the current understanding of Holocene climate variations in British Columbia. Because of the complex and at times topographically-controlled response of conifers to climate in the study area, this region may provide a particular challenge in terms of reconstructing Holocene climate variability.
| Identifer | oai:union.ndltd.org:uvic.ca/oai:dspace.library.uvic.ca:1828/3101 |
| Date | 15 November 2010 |
| Creators | Coulthard, Bethany L. |
| Contributors | Smith, Daniel J. |
| Source Sets | University of Victoria |
| Language | English, English |
| Detected Language | English |
| Type | Thesis |
| Rights | Available to the World Wide Web |
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