SEDIMENTOLOGICAL AND OXYGEN ISOTOPES ANALYSES OF SEDIMENT FROM CELESTINE LAKE, ALBERTA, CANADA, REVEAL SUBSTANTIAL HOLOCENE LAKE-LEVEL CHANGES

Oxygen isotope (δ¹⁸O) analyses of authigenic calcium carbonate sediment from a large suite of lakes in the Canadian Rocky Mountains have been interpreted to reveal a dry early Holocene (~10-7ka), wet middle Holocene (~7-2ka), and dry late Holocene (2ka-present). This expansive dataset points to large-scale shifts in the hydroclimate regime in western Canada over the last 10ka; however, quantitative data for lake-level change supporting this interpretation is lacking. Reconstructions of lake-level change create a more complete picture of regional paleohydrology by providing clear evidence for changes in the precipitation-evaporation (P-E) balance over time. Celestine Lake in Jasper National Park, Alberta, Canada, provides a unique opportunity to ground truth these δ¹⁸O interpretations of regional hydroclimate with the first record of significant (1-2m) and sustained (3ka) water level shifts for a lake in the Canadian Rockies. Modern sediments suggest the presence of a thermocline in the water column below which the pH is low enough to dissolve authigenic carbonates and leave behind only organic sediment. The sedimentary analysis of three cores taken on a shallow- to deep-water transect (0.85m, 3.15m, and 5.50m water depth) reveals changes in carbonate and organic matter content that can be interpreted as major, prolonged shifts in the depth of the thermocline in response to equal shifts in water level. This interpretation aligns with the “lacustrine carbon pump” concept, which has been observed in lakes in north-central United States, but has not been widely studied. The carbonate-rich shallow-water core and organic rich deep-water core constrain maximum and minimum water level. The disappearance of shallow-water carbonates from the mid-depth core from 7-2ka suggests a higher lake level during this period than from 10-7ka and 2ka-present when carbonate sediments dominate. The δ¹⁸O from the mid-depth and shallow-water cores agree with the regional isotope records and corroborate the lake-level record. Altogether, the Celestine Lake record indicates that the hydroclimate shifts reported by previous δ¹⁸O records within western Canada were large enough to cause sustained shifts in lake water level within the region.