Lodgepole pine and interior spruce radial growth response to climate and topography in the Canadian Rocky Mountains, Alberta

Climate change may have spatially variable impacts on growth of trees in topographically diverse environments, making generalizing across broad spatial and temporal extents inappropriate. Therefore, topography must be considered when analyzing growth response to climate. We address these topo-climatic relationships in the Canadian Rocky Mountains, focusing on lodgepole pine (Pinus contorta Douglas ex Louden) and interior spruce (Picea glauca (Moench) Voss × Picea engelmannii hybrid Parry) growth response to climate, Palmer drought severity index (PDSI), aspect, and slope angle. Climate variables correlate with older lodgepole pine growth on south- and west-facing slopes, including previous August temperature, winter and spring precipitation, and previous late-summer and current spring PDSI, but younger lodgepole pine were generally less sensitive to climate. Climate variables correlate with interior spruce growth on all slope aspects, with winter temperature and PDSI important for young and old individuals. Numerous monthly growth–climate correlations are not temporally stable, with shifts over the past century, and response differs by slope aspect and angle. Both species are likely to be negatively affected by moisture stress in the future in some, but not all, topographic environments. Results suggest species-specific and site-specific spatiotemporally diverse climate–growth responses, indicating that climate change is likely to have spatially variable impacts on radial growth response in mountainous environments.

Analysis of growing season carbon and water fluxes of a subalpine wetland in the Canadian Rocky Mountains: implications of shade on ecosystem water use efficiency

Mountain regions are an important regulator in the global water cycle through their disproportionate water contribution. Often referred to as the “Water Towers of the World”, mountains contribute 40 to 60% of the world’s annual surface flow. Shade is a common feature in mountains, where complex terrain cycles land surfaces in and out of shadows over daily and seasonal scales. This study investigated turbulent water and carbon dioxide fluxes over the snow-free period in a subalpine wetland in the Canadian Rocky Mountains, from June 7th to September 10th, 2018. Shading had a significant and substantial effect on water and carbon fluxes at our site. Each hourly increase of shade per day reduced evapotranspiration (ET) and gross primary production (GPP) by 0.42 mm and 0.77 gCm-2, equivalent to 17% and 15% per day, respectively, over the entire study period. However, during only peak growing season, when leaves were fully out and mature, shade caused by the local complex terrain, reduced ET and increased GPP, likely due to enhanced diffuse radiation. The overall result was increased water use efficiency at the site during periods of increased shading during the peak growing season. In addition to incoming solar radiation (Rg), temporal variability in ET was found to relate to temporal variability in soil temperature, moisture and vapour pressure deficit. Shade impacted the curvature and intercept of the nonlinear ET-Rg relationship at our site. In contrast, temporal variability in GPP at our site was dependent largely on Rg only. Our findings suggest that shaded subalpine wetlands can store large volumes of water for late season runoff and are productive through short growing seasons.

Using 10Be dating to determine when the Cordilleran Ice Sheet stopped flowing over the Canadian Rocky Mountains

During the last glacial maximum the Cordilleran and Laurentide ice sheets coalesced east of the Rocky Mountains and geomorphological evidence indicates ice flowed over the main ridge of the Rocky Mountains between ~54–56°N. However, this ice flow has thus far remained unconstrained in time. Here we use in situ produced cosmogenic 10Be dating to determine when Cordilleran ice stopped flowing over the mountain range. We dated eight samples from two sites: one on the western side (Mount Morfee) and one on the eastern side (Mount Spieker) of the Rocky Mountains. At Mount Spieker, one sample is rejected as an outlier and the remaining three give an apparent weighted mean exposure age of 15.6 ± 0.6 ka. The four samples at Mount Morfee are well clustered in time and give an apparent weighted mean exposure age of 12.2 ± 0.4 ka. These ages indicate that Mount Spieker became ice free before the Bølling warming and that the western front of the Rocky Mountains (Mount Morfee) remained in contact with the Cordilleran Ice Sheet until the Younger Dryas.

Supplemental Material: Regional fault-controlled shallow dolomitization of the Middle Cambrian Cathedral Formation by hydrothermal fluids fluxed through a basal clastic aquifer

Geochemical data for dolomite and limestone (trace element, rare earth element, carbon and oxygen stable isotope, clumped oxygen isotope, noble gas, fluid inclusion and bulk rock XRD) of the Middle Cambrian Cathedral Formation, Southern Canadian Rocky Mountains.

Supplemental Material: Regional fault-controlled shallow dolomitization of the Middle Cambrian Cathedral Formation by hydrothermal fluids fluxed through a basal clastic aquifer

Geochemical data for dolomite and limestone (trace element, rare earth element, carbon and oxygen stable isotope, clumped oxygen isotope, noble gas, fluid inclusion and bulk rock XRD) of the Middle Cambrian Cathedral Formation, Southern Canadian Rocky Mountains.

Glacier Cover Change Assessment of the Columbia Icefield in the Canadian Rocky Mountains, Canada (1985–2018)

Meltwater from glaciers makes significant contributions to general streamflow and provides water for flora and fauna. Continuous glacier monitoring programs enhance our understanding of the impacts of global warming on glaciers and their topographical features. The objective of this study is to measure spatial and temporal changes in Canada’s Columbia Icefield glaciers. This study uses Landsat (TM 5 and OLI) images to delineate glacier extents in the Columbia Icefield between 1985 and 2018. The study also analyzes the retreat of the Athabasca, Castleguard, Columbia, Dome, Saskatchewan, and Stutfield Glaciers. The total area covered by the Icefield in 1985 was 227 km2. By 2018, the Icefield had lost approximately 42 km2 of its area coverage, representing 18% of its previous coverage. All glaciers in the study region retreated and decreased in area over the study period. The pattern observed in this study is one of general ice loss in the Columbia Icefield, which mirrors patterns observed in other mountain glaciers in Western Canada.