Holocene paleohydrology of central Alberta: testing the general-circulation-model climate simulations

Abstract

Paleoecological investigations of 28 lakes and bogs provide the basis for a Holocene paleohydrological record for central Alberta. Shallow basins, empty during the early Holocene, began flooding shortly after 8000 years ago; most filled from 6500 to 4500 years ago, and none filled later than 3000 years ago. Pollen of a hypersaline indicator genus, Ruppia, was found in cores of lakes where the plant does not presently grow, indicating lower lake levels, evaporation stress, and increased salinity from 8000 to 3000 years ago. Moore Lake (54°30′N, 100°30′W) may have dropped 15 m from 9200 to 5900 years ago, and Lofty Lake (54°44′N, 112°29′W) largely dried up between 8700 and 6300 years ago. Lower water levels are suggested for several lakes by shifts in fossil diatom populations from planktonic to benthic, particularly epipelic species including pioneering taxa. These shallow, warm lakes were highly productive and sedimentary pigment levels reached maximum values between about 9000 and 4000 years ago.The paleohydrological record indicates early Holocene aridity, with the onset and development of moister conditions between 8000 and 3000 years ago, by which time modern climatic and vegetation conditions had been established. This record fits the Holocene climate predicted by the general-circulation-model simulations based on orbital perturbations.

River of Change: a Model for the Development of Terraces Along the Bow River, Alberta

“…In central Alberta at this time, shallow basin lakes began flooding as early as 7500 BP but salinity remained high as a result of continued high evaporation rates (Schweger and Hickman, 1989). Similar moisture deficits were recorded as dramatic changes in water levels within the deep basin lakes of the area (Schweger and Hickman, 1989). In short, the interval between 9000 and 5000 BP is best characterized as one of moisture deficits arising primarily from the high rates of evaporation.…”

“…In middle northern latitudes, precipitation increased around 9000 BP but evaporation increased even more, leading to soil-moisture deficits (Kutzbach and Guetter, 1986). In the mountains and in central Alberta, maximum aridity occurred at the beginning of the interval (Schweger and Hickman, 1989;Beierle and Smith, 1998) whereas further east the episode of moisture deficit lasted from 9000 to 6000 BP (Vance, 1986) with the greatest drought being recorded from 7700 to 6800 BP (Sauchyn and Sauchyn, 1991). In the mountains and foothills of Alberta, water levels in closed basin lakes dropped by 6 m, presumably reflecting a lowering of the water table and moisture deficits resulting from decreases in precipitation or increases in evaporation (Beierle, 1997;Beierle and Smith, 1998).…”

“…In the mountains and foothills of Alberta, water levels in closed basin lakes dropped by 6 m, presumably reflecting a lowering of the water table and moisture deficits resulting from decreases in precipitation or increases in evaporation (Beierle, 1997;Beierle and Smith, 1998). In central Alberta at this time, shallow basin lakes began flooding as early as 7500 BP but salinity remained high as a result of continued high evaporation rates (Schweger and Hickman, 1989). Similar moisture deficits were recorded as dramatic changes in water levels within the deep basin lakes of the area (Schweger and Hickman, 1989).…”

“…Thus, the rate of discharge depended largely on runoff from precipitation which also had decreased as indicated by the water levels in the mountain lakes (Beierle and Smith, 1998). Similarly, the lowered lake levels in central Alberta indicate a moisture deficit, even though precipitation increased during this interval primarily as summer storms (Schweger and Hickman, 1989). As a result, stream power was inadequate to remove the slowly accumulating sediment or even to move the fine sediments very far downstream.…”

Paleolimnology of Lake Manitoba: the Lithostratigraphic Evidence

“…Considerable recent effort has been made to decipher past regional environmental changes on the basis of multiple proxy investigations of these lacustrine records (Lemmen et al, 1993;Vance and Last, 1994;Lemmen, 1996;Vance, 1997;Lemmen and Vance, 1999a), however only a few of the lakes in the northern Great Plains of Canada have provided complete, uninterrupted Holocene sequences. As discussed by others (e.g., Schweger and Hickman, 1989;Yansa, 1995;Last, 1995Last, , 2002, fewer than a dozen continuous lacustrine stratigraphic sections in the entire interior plains region extend back to the early Holocene. Lake Manitoba, located on the eastern margin of the Great Plains ( Fig.…”