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.
Cloud overlap effects on general circulation model climate simulations
