HOLOCENE ENVIRONMENTAL VARIABILITY IN SUBALPINE ALBERTA: PROXY EVIDENCE FROM δ13C AND δ18O VALUES OF UPPER HOGARTH LAKE MARL

Please join us for a graduate student seminar this Friday November 23 at 3:30 pm in rm 155 Geology presented by Dustin Matkowski, MSc candidate:

HOLOCENE ENVIRONMENTAL VARIABILITY IN SUBALPINE ALBERTA: PROXY EVIDENCE FROM δ13C AND δ18O VALUES OF UPPER HOGARTH LAKE MARL

A 3.6-meter lake sediment core was recovered from Upper Hogarth Lake in the subalpine region of southwestern Alberta, Canada. The core provides proxy evidence for Holocene environmental variability over the last 12,000 years. The core was sub-sampled at millimeter resolution for δ18OCaCO3 and δ13CCaCO3 values, yielding over 750 samples. δ18OCaCO3 values record changes in the dominant seasonality of precipitation in the region that result from changing temperatures and atmospheric circulation, while variability in δ13CCaCO3 values record changes in basin ecology, soil moisture and local humidity.

Upper Hogarth Lake (50.793˚N, -115.319˚W) is located approximately 100km WSW of the city of Calgary, Alberta in the Kananaskis Range of the Canadian Rocky Mountains. It is situated in Quaternary glacial till overlying Devonian-Carboniferous carbonate bedrock at an elevation of 1,900masl. Upper Hogarth Lake is dimictic, with a surface area of 0.026 km2 and a maximum depth of <8m. It is hydrologically open with groundwater exchange and summer outflow. It is recharged via groundwater, snowmelt and rainfall. Precipitation of calcite that accumulates as marl occurs as encrustations on the macroscopic green algae Chara sp., with marl deposition beginning ~11.8 ka. The Upper Hogarth Lake age model was constructed using radiocarbon dating of eight terrestrial plant samples recovered from the core and by tephrochronology. Carbon-14 dates were calibrated to IntCal13 and plotted using the “Bacon” (v. 2.2) Bayesian Age-Depth Modelling package for “R” statistical software.

The core can be divided into 3 lithological zones: 1) basal diamict deposited following the retreat of the Cordilleran Ice Sheet; 2) inorganic mud, transitioning into organic gyttja deposited prior to 11.8 ka; and 3) cream-colored marl deposited from 11.8 ka to present. δ13CCaCO3 values range from -4.1‰ to +3.2‰ VPDB, reflecting a basin ecosystem evolving toward modern conditions, as well as variability in local soil moisture. δ18OCaCO3 values range from -18.8‰ to -13.0‰ VPDB recording Early Holocene warming with summer precipitation dominating the lake water recharge. δ18OCaCO3 and δ13CCaCO3 values suggest warm, arid Mid-Holocene summers with snowmelt being the primary source of lake recharge. Late Holocene δ18OCaCO3 and δ13CCaCO3 values represent the onset of Neoglacial conditions with an increase in summer precipitation toward present.