Late glacial ? early holocene palaeosalinity in Alberta, Canada ? climate implications

Abstract

Palaeolimnological and palynological records from climatically variable central Alberta, Canada, document periods of hypersaline lake conditions indicative of late glacial and early Holocene drought. The sensitivity of palaeolimnological indicators for inferring palaeoclimates is examined by comparing records from two sites at opposite ends of the regional precipitation gradient. Palaeosalinity is identified by the presence of Ruppia pollen, a hypersaline aquatic plant not presently growing in either lake, and diatom assemblages comprising both saline epipelic and planktonic species. Goldeye Lake (52027 ' N; ! 16 ~ 12' W), in the relatively moist Rocky Mountain Foothills remained saline from its inception before ca 14500 years BP until ca 10400 years BP by which time pioneering forests had replaced tundra vegetation; however, freshwater planktonic diatoms dominated ca 12500 to 11 500 years BP. However, dating problems endemic to the Foothills region make this chronology only tentative. Moore Lake (54 ~ 30' N; 110 ~ 30' N), in dry, east-central Alberta contained Ruppia only between ca 9000 and 6000 years BP. Freshwater diatoms dominated until ca 10000 years BP when they were succeeded by taxa characteristic of saline water. The lake remained saline until ca 6000 years BP. The late glacial period of palaeosalinity at Goldeye Lake occurred because the lake was surrounded by Cordilleran and Laurentide glacial ice, and therefore, cut off from moisture sources until the early Holocene by which time significant ice recession had occurred. Factors causing the second period of salinity remain unknown at this time. In contrast, by the early Holocene, Moore Lake was influenced by drought caused by high summer insolation induced by orbital fluctuations. Freshwater conditions were maintained through the Holocene in the Foothills region of west-central Alberta, but occurred consistently only over the last 4000 years in central and east-central Alberta. The warmer, drier climate during the early Holocene did affect lake levels in at least one headwater Foothills lake (Fairfax Lake -52 ~ 58' N; 116 ~ 34' W). The severity of the drought increased in an easterly direction across the province.

Century scale paleoclimatic reconstruction from Moon Lake, a closed‐basin lake in the northern Great Plains

“…In addition, in central Alberta an early Holocene arid period occurs from -12,000 to 6000 B.P. (Hickman and Schweger 1993), with many paleolimnological indications of lower lake levels and increased salinity from -8000 to 3000 B.P. (Schweger and Hickman 1989).…”

Potential effects of climate change on ion chemistry and phytoplankton communities in prairie saline lakes

“…Saline lake paleoecology has been a valuable tool for determining past climate trends in both temperate (Fritz et al 199 1) and subarctic (Pienitz et al 1992) North American lakes, while examining mineral deposition processes in saline lakes and playas may also provide considerable information on past environmental and hydrological conditions (Last 1994). Sedimentary studies combining both biological and mineralogical techniques have been used to determine past salinity changes in Canadian prairie lakes (Hickman and Schweger 1993;Van Stempvoort et al 1993) on a long-term basis; however, these core-based studies lack the fine resolution needed to examine the…”

Assessment of Climate Change and Freshwater Ecosystems of the Rocky Mountains, Usa and Canada

“…Recent studies have con®rmed that glaciers in the main ranges of the central Canadian Rockies quickly receded between 11 500 and 10 000 years before present (BP) (Reasoner and Rutter, 1988;Reasoner and Hickman, 1989;Reasoner et al, 1994). The onset and rate of glacial recession depended on latitude, elevation, aspect and longitudinal position within the mountain ranges (Luckman, 1990;Hickman and Schweger, 1993). In general, early Holocene climates were considered to be signi®cantly warmer (1±1 .…”

“…Similarly, glaciers are less common in rain shadow regions or on south-facing slopes than at other sites. For example, Hickman and Schweger (1993) showed that lakes in the eastern Rocky Mountain foothills and plains were initially saline in the early Holocene because glaciers blocked the¯ow of moist Paci®c air. However, as glaciers melted, present day circulation was established, and lakes freshened.…”