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Home , Peyto Glacier, Ram River, Terminal moraine

Tree-Ring Based Estimates of Mass Balance in the Northern for the Past 300 Years 1,2Gregory T. Pederson, 3Emma Watson, 4Brian Luckman, 1Daniel B. Fagre, 5Stephen T. Gray, 2Lisa J. Graumlich [email protected], [email protected], [email protected], [email protected], [email protected], [email protected] (1) U.S. Geological Survey - NRMSC - Glacier Field Station, West Glacier, MT 59936, USA, (2) Big Sky Institute - Montana State University, Bozeman, MT 59717, USA, (3) Research Branch, Meteorological Service of , Environment Canada, Downsview, Ontario, Canada M3H 5T4, (4) Department of Geography, University of Western Ontario, London Ontario, Canada N6A 5C2, (5) Geological Survey - Desert Laboratory, Tucson, AZ, USA 85745

INTRODUCTION Boulder Glacier Summer 1988 (a) Alpine in the U.S. and Canadian Rocky Mountains reached their maximum Holocene extent during the Little (LIA: Luckman 2000, Carrara 1989). Subsequently, glaciers throughout the region have undergone dynamic and sometimes rapid phases of frontal recession (Carrara 1989, Luckman 2000, Key et al. 2002). Recent glacier research has focused on developing detailed histories of glacier fluctuations throughout the LIA. These data, though sparse, indicate multiple periods of glacier advance during the LIA, and that the timing of maximum advance within the may not have been synchronous (Figure 1a; Luckman 2000). dates at several of the northernmost (b) glaciers studied, e.g. in , indicate maximum glacier extent between 1700 and 1750 Photo by J. DeSanto (Luckman 2000) whereas further south, e.g. in Kananaskis and Glacier National Park (GNP), the LIA Summer 1932 maximum glacial extent occurred between ca. 1800-1850 (Carrara 1989, Smith et al. 1995, Luckman 2000, Key et al. 2002). mean SWE (n=25) mean SWE Northern PC (n=10) Mass balance records for this region are sparse consisting of two records from the Canadian Rockies mean SWE Southern PC (n=7) (Peyto 1965- present and Glacier 1965-75). In order to develop a better understanding of glacier fluctuations in this region, Watson and Luckman (2004) and Pederson et al. (2004) independently investigated the paleoclimatic drivers of glacier fluctuations using data derived from tree-ring Figure 3. Plots of April 1st standardized SWE Figure 4. Plots of standardized seasonal maximum th chronologies for two sites located along the Continental Divide (Figure 1b). We present a comparison of records over the 20 century. (a) standardized (Tmax) and minimum (Tmin) temperature records over the Photo by G. Grant th these two proxy-based attempts of reconstructing for in , and SWE values at 25 stations (see Figure 1). (b) 20 century. (a) mean summer Tmax anomalies for 14 the glaciers in GNP, Montana. We also use instrumental and proxy climate data to investigate whether (Left) The Snout of the Athabasca Glacier – Jasper National Park, Alberta - viewed from the same mean annual SWE values for the 25 stations in meteorological stations (see Figure 1). (b) mean differences between these proxy mass balance series reflect regional differences in mass balance over point in 1917 and 1986. Over this 70-year period the Athabasca Glacier retreated 1.5 km. (a) and smoothed with a 10-year spline. summer Tmin anomalies for the 14 stations in (a). All time, or whether they result from differences in the approach and data used to develop the (Right) The Boulder Glacier located in Glacier National Park, Montana. During the mid-19th century the records in (a) and (b) have been smoothed using a 10yr reconstructions. In doing so, we begin to explore differences in timing of the LIA maximum glacial boulder glacier extended across boulder pass leaving a prominent terminal moraine. Today all that spline. (c) mean annual and smoothed (10yr spline) remains is a stagnant ice apron. values for spring (MAM) and summer (JJA) T . advance. SUMMARY AND CONCLUSIONS min Though careful interpretation and record selection is required, tree-ring based proxy records of (a) (b) climate allow the reconstruction of continuous records of glacier changes. In the absence of long- term instrumental records, they permit exploration of the relative contribution of changes in temperature and precipitation to net mass balance. Here, both proxy records indicate decadal- and longer-term trends in winter snowpack and summer temperature have a significant influence on the net mass balance of regional alpine glaciers. Instrumental records suggest the minor north to south differences in the relative extent of 18th and 19th century glaciers may have been due to slight differences in SWE (e.g. Figure 3) or reduced temperatures along the gradient. These two preliminary attempts at modeling past glacier fluctuations helped to identify the various scales of the forcing factors and therefore possibly identify their causes. Results also indicate the potential to

Number of Number develop a more comprehensive picture of how glaciers have fluctuated in the past, thereby providing insight on how future modeled or actual climate changes may influence them into the 21st century.

1300 1500 1700 1900 Figure 1. (a) Dated LIA moraines in the Canadian Rockies. Moraines ages are based on Figure 2. Comparison of seasonal and net mass balance proxies for Peyto Glacier and Glacier National dendrochronology at 48 glaciers and lichenometry at another 18 glaciers. The ages are grouped into Park. (Top) Standardized seasonal and net mass balance estimates for Peyto Glacier including the 25-year increments. Graph reproduced from Luckman (2000). (b) Location of Peyto Glacier, Alberta regression beta values for tree-ring data (locations given in Figure 1). (Bottom) Reconstructions used to and Glacier National Park, Montana. Selected meteorological stations and tree-ring chronology sites infer potential seasonal mass balance for the Glacier National Park region. All annual values have been used to develop the Peyto Glacier mass balance reconstructions are shown. The larger scale map smoothed using a 10 yr spline (thick colored line). shows stations located along the Continental Divide from which snow water equivalent (SWE) and EVALUATING THE DIFFERENCES – Instrumental and Proxy Records temperature records were obtained. Throughout the region SWE records display coherent decadal-scale variability that corresponds with sea Figure 5. Tree-ring derived records that are related to sea surface temperatures in the Pacific Ocean and surface temperature patterns in the North Pacific (i.e. PDO: Figure 3). PCA analysis reveals northern and winter mass balance in the study area. The Gedalof and Smith, 2001 and Biondi et al., 2001 series are COMPARISON OF MASS BALANCE PROXY RECORDS southern regions differing primarily in magnitude of major periods of above and below average SWE. reconstructions of PDO. Miners Well is a mountain hemlock tree ring-width chronology from the Gulf of Records of summer T and T exhibit strong regional coherence (Figure 4a,b). Estimated summer Alaska developed by G. Wiles, P.E. Calkin and D. Frank. All series have been smoothed with a 10-yr A fundamental difference between these two mass balance reconstructions is that approximately 30 min max spline. years of mass balance data were available for Peyto Glacier that allow direct calibration of mass balance balance at Peyto Glacier and for the GNP region are strongly correlated with instrumental summer Tmax estimates, whereas no mass balance data were available for the GNP study . Therefore the latter case (with 11/15 stations [r=-0.22 to -0.528] for Peyto, and 13/15 stations [r=-0.36 to -0.65] for GNP). Between REFERENCES relied on a detailed history of glacier length and estimated retreat rates for the Agassiz and Jackson 1920 and 1990 no linear trend is present in summer Tmax – interdecadal variability dominates. However, Biondi, F., Gershunov, A. and Cayan, D.R. 2001. North Pacific decadal climate variability since 1661. Journal of Climate, th 14: 5-10. Glaciers (Carrara 1989, Key et al. 2002) to evaluate correspondence between the glaciers and inferred records of spring and summer Tmin show a strong trend over the 20 century (Figure 4c), which is consistent mass balance histories. for all seasons. Such changes in Tmin may extend the period of melting, shift the rain:snow input ratio, and Carrara, P.E. 1989. Late quaternary glacial and vegetative history of the Glacier National Park region, Montana. U.S. maintain higher summer ablation rates. Similarities between instrumental temperature and SWE records Geological Survey Bulletin, 1902, 64pp. Though the methods and data used to infer and reconstruct glacier mass balance are quite different suggest mass balance patterns should be regionally similar. Therefore, differences between reconstructions D’Arrigo, R., Villalba, R. and Wiles, G. 2001. Tree-ring estimates of Pacific Decadal variability. Climate Dynamics, 18: 219- between studies, interesting similarities and differences arise between the balance estimates. The may be more readily explained by differences in proxies used to estimate net mass balance values. 224. winter and summer balance records in both regions exhibit strong decadal and multi-decadal variability, Gedalof, Z., Mantua, N.J. and Peterson, D.L. 2002. A multi-century perspective of variability in the Pacific Decadal with the winter balance proxies often sharing common periods of above and below average accumulation Each winter mass balance proxy relied on ocean-atmosphere teleconnections related to temperature and Oscillation: new insights from tree rings and coral. Geophysical Research Letters. 29: doi:10.1029/2002GL015824. pressure patterns in the North Pacific (i.e. PDO) since no winter precip. sensitive local chronologies were events (Figure 2). For example, there is general correspondence between records from the 1770s- Gedalof, Z. and Smith, D.J. 2001. Interdecadal climate variability and regime-scale shifts in Pacific North America. 1790s, throughout the 19th century, and a common period of high accumulation beginning in the mid- found. However, this assumes that the PDO operated in a similar manner (with similar variability) prior to the Geophysical Research Letters, 28: 1515-1518. period of instrumental record. Disagreement, between published PDO reconstructions prior to ca. 1840 1940s to the late-1970s. Differences in estimated winter balance arise with above average accumulation Key, C.H, Fagre, D.B., and Menicke, R. K. 2002: Glacier retreat in Glacier National Park, Montana. In: Williams Jr., R. S., predicted for the early-1700s and early-20th century at Peyto Glacier, while the D’Arrigo et al. (2001) suggests this assumption may be violated (Figure 5; Gedalof et al. 2002), thus it is important that inferred and J. G. Ferrigno (Eds.), Satellite Image Atlas of Glaciers of the World, Glaciers of North America - Glaciers of the PDO reconstruction (used to estimate GNP winter balance) indicates average to below average trends and variability in winter SWE conditions are confirmed by multiple lines of independently derived Western United States. United States Government Printing Office, Washington D.C., USA, pp. J365-J381. accumulation for the GNP region. Fewer similarities exist between the regional records of summer evidence. Another interesting difference between regional mass balance proxies is the long-term trend Luckman, B.H. 2000. The in the Canadian Rockies. Geomorphology, 32: 357-384. balance; however, there are two prominent periods of correspondence between records with (cool) towards negative summer and net mass balance at Peyto Glacier. The linear trend towards higher ablation Luckman, B.H. and Wilson, R.J.S. 2005. Summer temperatures in the Canadian Rockies during the last millennium – a summer conditions predicted for the early-1700s and early- to mid-1800s. Pronounced disparities rates at Peyto Glacier is caused by the Athabasca summer Tmax reconstruction, which exhibits increases in revised record. Climate Dynamics, doi: 10.1007/s00382-004-0511-0. between summer balance estimates arise with average to high summer ablation rates predicted between Tmax beginning ca. 1825. This trend is not evident in the GNP summer and net balance proxies, in part, Pederson, G.T., Fagre, D.B., Gray, S.T. and Graumlich, L.J. 2004. Decadal-scale climate drivers for glacial dynamics in ca. 1720s-1770s and 1850s-1880s for GNP, when low ablation conditions are reconstructed for Peyto because the tree-ring chronologies contain a mixed temperature and precipitation signal that may not Glacier National Park, Montana, USA. Geophysical Research Letters, 31: L12203, doi:10.1029/2004GL019770. Glacier. The most striking difference however, is the long-term linear trend towards higher summer consistently track summer melt. Also, the mixed climate signal contained in drought reconstructions does Smith, D.J., McCarthy, D.P., Colenutt, M.E. 1995. Little Ice Age glacial activity in Peter Lougheed and Elk Lakes Provincial ablation rates (ca. 1880) at Peyto Glacier, which consequently drives the 20th century negative trend in not retain the centennial-scale variability seen in temperature reconstructions. Neither reconstruction Parks, Canadian Rocky Mountains. Canadian Journal of Earth Sciences. 32: 579-589. net mass balance. includes, or necessarily captures the aforementioned trends in Tmin, making the assessment of this Watson, E. and Luckman, B.H. 2004. Tree-ring-based mass-balance estimates for the past 300 years at Peyto Glacier, potentially important variable difficult. Alberta, Canada. Quaternary Research, 62: 9-18.