Understanding spatial patterns of past aridity on the Canadian prairies over the Holocene: insights based on diatom assemblages from Success Lake

Abstract

The Canadian prairies receives little precipitation and hence is prone to drought-related environmental, economic, and social impacts. Previous studies have suggested the Canadian prairies are sensitive to extreme droughts, and during the warmer mid-Holocene, many lakes became increasingly saline or dried out. Understanding the Holocene aridity profile is critical for us to be able to confidently forecast future drought and aridity, which is essential to establish appropriate policies and programs to reduce negative impacts. Diatom assemblages preserved in Success Lake sediment were used to reconstruct changes in lake-water salinity, with increases in salinity, serving as a proxy of enhanced aridity over the Holocene on the Canadian prairies. The diatom record from Success Lake revealed four periods that were defined based on diatom composition. Century-scale analysis of the diatom record during the Holocene is consistent with a drier climate in the mid Holocene (between ~7,000 to ~5,300 cal yr BP) and is represented by high abundance of Cyclotella choctawhatcheeana. Between ~5,300 cal cal yr BP to 3,300 cal yr BP, short-lived high frequency in Chaetoceros muelleri implies the period of wetter events within sustained arid conditions throughout the mid-Holocene. Analysis of the past ~3,000 years suggests that the late Holocene was more complex, with extended periods of increased variability in diatom assemblages and inferred salinity suggesting frequent oscillation between the rise and falls in effective moisture. The mechanism controlling the moisture gradient is likely associated with the change in intensity and shape of the jet stream, influenced by ocean-atmospheric interaction and solar radiation. Comparing the record from Success Lake with other paleoclimatic records from the Canadian prairies and regions from near the ecotone of mixed-grass prairies and the Aspen parkland, show that lakes on the mixed-grass prairies experienced much less intense variation in effective moisture than the lakes adjacent to the Aspen Parkland region, highlighting this ecotone to variations in effective moisture.