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Stable oxygen isotopes measured in tree rings are useful for reconstructing climate variability and explaining changes in physiological processes occurring in forests, complementing other tree-ring parameters such as ring width. Here, we analyzed the relationships between different climate parameters and annually resolved tree-ring δ18O records (δ18OTR) from white spruce (Picea glauca [Moench]Voss) trees located near Tungsten (Northwest Territories, Canada) and used the NASA GISS ModelE2 isotopically-equipped general circulation model (GCM) to better interpret the observed relationships. We found that the δ18OTR series were primarily related to temperature variations in spring and summer, likely through temperature effects on the precipitation δ18O in spring, and evaporative enrichment at leaf level in summer. The GCM simulations showed significant positive relationships between modelled precipitation δ18O over the study region and surface temperature and geopotential height over northwestern North America, but of stronger magnitudes during fall-winter than during spring–summer. The modelled precipitation δ18O was only significantly associated with moisture transport during the fall-winter season. The δ18OTR showed similar correlation patterns to modelled precipitation δ18O only during spring–summer when water matters more for trees, with significant positive correlations with surface temperature and geopotential height, but no correlations with moisture transport. Overall, the δ18OTR records for northwestern Canada reflect the same significant large-scale climate patterns as precipitation δ18O for spring–summer, and therefore have potential for reconstructing past atmospheric dynamics in addition to temperature variability in the region. [ABSTRACT FROM AUTHOR]

Abstract: Modelling of tree-ring δ13C and δ18O data from the Columbia Icefield area in the eastern Rocky Mountains of western Canada provides fuller understanding of climatic and hydrologic variability over the past 1000 yr in this region, based on reconstruction of changes in growth season atmospheric relative humidity (RH grs), winter temperature (T win) and the precipitation δ18O–T win relation. The Little Ice Age (~AD 1530s–1890s) is marked by low RH grs and T win and a δ18O–T win relation offset from that of the present, reflecting enhanced meridional circulation and persistent influence of Arctic air masses. Independent proxy hydrologic evidence suggests that snowmelt sustained relatively abundant streamflow at this time in rivers draining the eastern Rockies. In contrast, the early millennium was marked by higher RH grs and T win and a δ18O–T win relation like that of the 20th century, consistent with pervasive influence of Pacific air masses because of strong zonal circulation. Especially mild conditions prevailed during the “Medieval Climate Anomaly” ~AD 1100–1250, corresponding with evidence for reduced discharge in rivers draining the eastern Rockies and extensive hydrological drought in neighbouring western USA. [Copyright &y& Elsevier]

Tree-ring based mass balance reconstructions developed for Peyto Glacier, Alberta, Canada are compared with measured conditions in the Pacific Ocean over the last century and, using reconstructions of Pacific climate indices, over the past ∼ 300 years, at interannual and decadal–interdecadal timescales. Tree-ring reconstructed winter balance totals at Peyto Glacier in La Niña, negative Pacific Decadal Oscillation (PDO) and La Niña/negative PDO years significantly exceed those in El Niño, positive PDO and El Niño/positive PDO years, respectively. The same phase pairings of reconstructed summer mass balance do not differ significantly. These findings confirm those seen in the measured mass balance records and shorter (100 years) tree-ring and instrumental climate record-based reconstructions, suggesting similar relationships have existed over the past ∼ 300 years. Maps showing the regression of Pacific sea surface temperatures (SSTs) on the seasonal mass balance series indicates that both winter and, albeit more weakly, summer mass balance series are related to ENSO-like patterns of SST variability in the Pacific Ocean at both interannual and interdecadal timescales. [ABSTRACT FROM AUTHOR]

Tree rings were used to reconstruct mass balance for Peyto Glacier in the Canadian Rocky Mountains from A.D. 1673 to 1994. Summer balance was reconstructed from tree-ring estimates of summer temperature and precipitation in the Canadian Rockies. Winter balance was derived from tree-ring data from sites bordering the Gulf of Alaska and in western British Columbia. The models for winter and summer balance each explain over 40% of the variance in the appropriate mass-balance series. Over the period 1966–1994 the correlation between the reconstructed and measured net balances is 0.71. Strong positive mass balances are reconstructed for 1695–1720 and 1810–1825, when higher winter precipitation coincided with reduced ablation. Periods of reconstructed positive mass balance precede construction of terminal moraines throughout the Canadian Rockies ca. 1700–1725 and 1825–1850. Positive mass balances in the period 1845–1880 also correspond to intervals of glacier readvance. Mass balances were generally negative between 1760 and 1805. From 1673 to 1883 the mean annual net balance was +70 mm water equivalent per year (w.e./yr.), but it averaged -317 mm w.e./yr from 1884 to 1994. This reconstructed mass balance history provides a continuous record of glacier change that appears regionally representative and consistent with moraine and other proxy climate records. [Copyright &y& Elsevier]

Two independent reconstructions of maximum May-August temperatures are developed from a new network of Engelmann spruce tree-ring chronologies at treeline sites across Interior British Columbia (IBC). The IBC reconstruction (AD 1600-1997) uses the longest three ring-width (RW) and two maximum latewood density (MXD) chronologies from the region. The shorter (regional) reconstruction (REG, 1845-1997) is based on an independent, more broadly based network of chronologies (12 RW and 5 MXD) and verifies the regional signal in the parsimoniously sampled IBC reconstruction. Both models explain 53% of the regional temperature variance (1912-1995) and correlate strongly (r = 0.92) over their common period. The IBC reconstruction indicates two prolonged cooler intervals, c. 1620-1710 and 1775-1880, separated by warmer conditions that approached late twentieth-century normals between c. 1710 and 1730. The mean anomaly over the 1600-1900 period is estimated at 0.38°C below the 1961-1990 mean with the seventeenth century (1601-1700) being marginally colder than the nineteenth century (-0.53: -0.49°C). Both reconstructions model the rise in temperatures from the 1880s to 1940s and indicate that maximum summer temperatures since 1930 have been warmer than at any period since 1600. The IBC record from 1600-1900 is very similar to the mean summer-temperature record reconstructed in the adjacent Canadian Rockies, providing mutual verification for the regional nature of the signal in both reconstructions. This is the first maximum summer-temperature reconstruction from North America. Significant changes are also noted in the relationships between summer mean, maximum and minimum temperatures in this region in the last few decades with a greater absolute rate of increase in mean and minimum temperatures. These changing relationships suggest it is prudent to model tree-ring response to a variety of temperature parameters rather than using mean-temperature values. [ABSTRACT FROM AUTHOR]

Investigates relationships between a network of 53 ring-width chronologies developed from low-elevation stands of Douglas-fir and ponderosa pine in the southern Canadian Cordillera and monthly, seasonal, and annualized climatic parameters (precipitation, temperature, and Palmer Drought Severity Index (PDSI)) using correlation analyses. Details of the study; Results; Discussion of the potential for reconstructing annual (and (or) summer) precipitation for sites across the region.

Examines the paleotemperature record from Picea engelmannii tree-line sites in Canadian Rockies, British Columbia. Differences in tree species modelling techniques, spatial coverage and seasonal temperatures; Development of temperature reconstruction for the Banff-Jasper region; Regional estimates of temperature.

Seven Douglas fir (Pseudotsuga menziesii) tree-ring chronologies were developed from sites in Banff and Jasper National Parks, Alberta, and near Cranbrook, British Columbia. The chronologies ranged in length from 191 to 691 years and display a strong precipitation signal. Multiple regression models were developed that calibrate .50% of the variance in the instrumental records and were used to reconstruct annual (pAugust– July or pJuly–June) precipitation for Banff, Jasper and Cranbrook. Comparison of these reconstructions with records from adjacent areas indicates that periods of reduced precipitation occurred over this region in c. ad 1760–1775, the 1790s, the 1840s–1870s, the 1890s and c. 1920–1945. Periods of significantly greater precipi-tation occurred during the 1880s–1920s and in the latter half of the twentieth century. The Banff reconstruction extends back to ad 1430 and also shows major drier intervals c. 1470–1510, the 1570s and 1615–1660. These reconstructions indicate regionally coherent precipitation patterns that fluctuate on decadal timescales and may be linked to changes in atmospheric circulation patterns. [ABSTRACT FROM AUTHOR]

This paper presents examples of environmental changes in the Canadian Rockies in the context of a 1.5 deg. C increase in mean annual temperatures over the last 100 years. During this period increases in winter temperatures have been more than twice as large as those during spring and summer. Glacier cover has decreased by at least 25% during the present century and glacier fronts have receded to positions lastoccupied ca. 3000 years ago. These two lines of evidence suggest that the climate of the late 20th century is exceptional in the context of the last 1000 to 3000 years. Detailed studies in three closely located upper treeline sites document variable responses of vegetation to climate change that reflect species differences as well as local differences in microclimate and site conditions. Treeline has advanced upslope in response to climate warming, but site and species differences control the rate and nature of the advance. Human impacts on the environment compound the changes due to climate warming. Historic photographs indicate significant changes in the type and density of forest cover due to the absence of significant forest fires within these National Parks during the last 70-80 years. The visual impact of these changes, which partially reflects a policy of fire suppression, is far greater than the impact of changes associated with more direct tourist-related impacts. It is therefore important that monitoring programs examine vegetation changes over the entire landscape rather thanfocusing exclusively on supposedly climate-sensitive sites. [ABSTRACT FROM AUTHOR]

Abstract: Castle Creek Glacier in the Cariboo Mountains of British Columbia remained close to its Little Ice Age limit for most of the past 1500 years, without significant recession until the 20th century. This conclusion is based on radiocarbon-dated detrital and in-situ plant material overrun by the glacier, and the sedimentary record from informally named On–off Lake, which received clastic sediments only when Castle Creek Glacier crossed a hydrologic divide 330 m upvalley of the Little Ice Age limit. Plant macrofossils recovered from the transition between basal inorganic silt and overlying organic silty clay in a sediment core from the lake indicate that the glacier first retreated behind the divide ca. 10.92–9.70 ka. Ages of 8.97–8.61 and 5.58–5.53 ka on detrital wood from the glacier''s forefield may record earlier advances, but the first unequivocal evidence of glacier expansion is from an overridden stump with an age of 4.96–4.45 ka. Continuous accumulation of gyttja within On–off Lake, however, indicates that Castle Creek Glacier did not cross the hydrologic divide at any time during the first half of the Holocene. Glacigenic sediments began to accumulate in the lake between 2.73 and 2.49 ka, indicating that Castle Creek Glacier expanded beyond the hydrologic divide at that time. A coincident advance is also recorded in the northern Rocky Mountains of British Columbia at Kwadacha Glacier, which overran a vegetated surface at 2.69–2.36 ka. Clastic sedimentation in On–off Lake ceased soon after the Bridge River volcanic eruption (2.70–2.35 ka), indicating that Castle Creek glacier retreat to a position upvalley of the divide at that time. Sedimentation resumed before 1.87–1.72 ka when the glacier advanced again past the hydrologic divide. Following a second retreat, Castle Creek Glacier advanced across the divide a final time at ca. 1.54–1.42 ka. The snout of the glacier remained less than 330 m upvalley of the Little Ice Age moraine until the early twentieth century when annual moraines indicate rapid frontal recession to a position upvalley of the hydrologic divide. These data collectively indicate that glaciers in the Cariboo Mountains of British Columbia nearly achieved their all-time Holocene limits as early as 2.73–2.49 ka and climatic conditions in the early 20th century abruptly ended a 1500-year period favoring glacier expansion. [Copyright &y& Elsevier]

Abstract: Most Quaternary research in Canada during the first half of the twentieth century focused on Pleistocene glaciation. Given the dramatic shifts in climate during the Pleistocene, it is not surprising that the Holocene was viewed as a time of benign climate. Holocene climate variability was first recognized around the middle of the century when paleoecologists found evidence that the early part of the epoch was warmer and drier than the later part. In 1970s and 1980s, another generation of geologists, geographers, and botanists began to recognize more complexity in Holocene climate and vegetation in western Canada. Several millennial-scale glacier “advances” postdating the early Holocene warm interval were defined, including the Garibaldi Phase (6.9–5.6 ka), the Tiedemann–Peyto Advance (3.5–1.9 ka), and the Little Ice Age (AD 1200–1900). Subsequently, application of dendrochronological techniques and stratigraphic studies in glacier forefields showed that the Little Ice Age was itself more complex than previously thought. During that 700-year period, glaciers repeatedly advanced and retreated in response to climatic variability on time scales ranging from centuries to decades. Recent work shows that the glacier record of the Garibaldi Phase and the Tiedemann and Peyto advances are similar in complexity to the Little Ice Age, with multiple advances of glaciers separated by intervals of more restricted ice cover. Researchers have also identified other times in the Holocene when glaciers expanded from restricted positions – 8.20, 4.90–3.80, and 1.70–1.40 ka. Continued research undoubtedly will reveal additional complexities, but with what is currently known the appropriateness of terms such as “Tiedemann Advance,” “Peyto Advance,” and “Little Ice Age” can be questioned. Only short periods of time separate these episodes as currently defined, and it seems likely that intervals of restricted glacier cover within each of these millennial-length intervals are just as long as the intervals separating them. [Copyright &y& Elsevier]