The Late Quaternary palaeoenvironmental history of a presently deep freshwater lake in east-central Alberta, Canada and palaeoclimate implications

The palaeoenvironmental history of Moore Lake, Alberta, Canada (54°30′N; 110°30′W) has been investigated through analysis of pollen, diatoms, total chrysophyte stomatocysts, and sedimentary pigments, including the blue-green algal xanthophylls, oscillaxanthin and myxoxanthophyll. The initial lake was shallow. Vegetation of the region was treeless and no doubt reflected the unique late-glacial pioneering environment. Planktonic diatoms characteristic of a deep, eutrophic lake were dominant by ca. 11400 yr B.P., when a birch-spruce-dominated Boreal Forest developed. However, in response to early Holocene warmth and aridity the lake had become saline by ca. 10,000 yr B.P. when Chaetoceros spp. and Cyclotella caspia became dominant, while an open parkland/grassland vegetation had developed, subject to increased fire frequency. Freshwater taxa reappeared between ca. 9100 and ca. 8400 yr B.P. providing evidence of a wetter period. However, after ca. 8400 yr. B.P. planktonic saline taxa returned as dominants. By ca. 6200 yr B.P. birch-spruce forests were once again developed in the area in response to more effective precipitation. Between ca. 5800 and 4000 yr B.P. oscillations between fresh and saline diatom taxa occurred suggesting some aridity reversals. During the last ca. 4000 years planktonic eutrophic diatom taxa dominated. Diatom numbers were initially low but increased ca. 11,400 yr B.P. and remained high until ca. 10,000 yr B.P. They were minimal during the saline interval. Afterwards as the lake freshened numbers of diatoms increased and several large peaks occurred, perhaps in response to internal nutrient loading coupled with increased runoff and erosion. Oscillaxanthin concentrations were initially high, but during the saline interval they became undetectable, except during the freshwater interlude, and then, as the lake became fresh large maxima occurred. In contrast, myxoxanthophyll concentrations were high during this saline interval. Large myxoxanthophyll peaks occurred simultaneously with those of oscillaxanthin as the lake freshened. Overall lake palaeoproduction levels during the Holocene appear to have altered little. The Moore Lake record demonstrates short-lived palaeoclimatic changes of unknown cause superimposed upon the broad trends, and the value of the palaeolimnological record which can be much more sensitive than fossil pollen vegetation reconstruction in demonstrating climate history. Results are compared with others for western Canada and the Great Plains.