THE LATE QUATERNARY PALEOENVIRONMENTAL HISTORY OF A PRESENTLY DEEP FRESH-WATER LAKE IN EAST-CENTRAL ALBERTA, CANADA AND PALEOCLIMATE IMPLICATIONS

The palaeoenvironmental history of Moore Lake, Alberta, Canada (54 deg rees 30'N; 110 degrees 30'W) has been investigated through analysis of pollen, diatoms, total chrysophyte stomatocysts, and sedimentary pigm ents, including the blue-green algal xanthophylls, oscillaxanthin and myxoxanthophyll. The initial lake was shallow. Vegetation of the regio n was treeless and no doubt reflected the unique late-glacial pioneeri ng environment. Planktonic diatoms characteristic of a deep, eutrophic lake were dominant by ca. 11400 yr B.P., when a birch-spruce-dominate d Boreal Forest developed. However, in response to early Holocene warm th and aridity the lake had become saline by ca. 10,000 yr B.P. when C haetoceros spp. and Cyclotella caspia became dominant, while an open p arkland/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 y r 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 respo nse 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 eut rophic diatom taxa dominated. Diatom numbers were initially low but in creased 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 f reshened numbers of diatoms increased and several large peaks occurred , perhaps in response to internal nutrient loading coupled with increa sed runoff and erosion. Oscillaxanthin concentrations were initially h igh, but during the saline interval they became undetectable, except d uring the freshwater interlude, and then, as the lake became fresh lar ge maxima occurred. In contrast, myxoxanthophyll concentrations were h igh during this saline interval. Large myxoxanthophyll peaks occurred simultaneously with those of oscillaxanthin as the lake freshened. Ove rall lake palaeoproduction levels during the Holocene appear to have a ltered little. The Moore Lake record demonstrates short-lived palaeocl imatic changes of unknown cause superimposed upon the broad trends, an d the value of the palaeolimnological record which can be much more se nsitive than fossil pollen vegetation reconstruction in demonstrating climate history. Results are compared with others for western Canada a nd the Great Plains.