Multidecadal to millennial‐scale shifts in drought conditions on the Canadian prairies over the past six millennia: implications for future drought assessment

Abstract

Three high-resolution climatic reconstructions, based on diatom analyses from lake sediment cores from the Canadian prairies, show that shifts in drought conditions have prevailed on centennial to millennial time scales for at least the past six millennia. These shifts in mean aridity exhibit broad regional synchrony, with particularly pronounced shifts at all sites between $ 1700-2000 cal. yr BP and $ 3600-3900 cal. yr BP, as well as at $ 5400-5500 cal. yr BP for the two sites which extend back to at least 6000 cal. yr BP. The two Saskatchewan lakes exhibited significant coherence in both the timing and direction of these shifts, whereas inferred changes at the westernmost site in Alberta were significantly correlated to the Saskatchewan sites, but opposite in sign, and exhibited more high-frequency variation on the scale of centuries. The mechanisms behind these abrupt shifts in aridity are poorly understood, but may be linked to changes in oceanicatmospheric interactions that influence the mean position of the jetstream and the associated storm tracks. Natural shifts in mean climatic conditions may accelerate with increasing carbon dioxide levels intensifying the likelihood of extreme droughts in North American prairies.

Spatial and temporal variability of prairie lake hydrology as revealed using stable isotopes of hydrogen and oxygen

“…In contrast, our analyses suggest that changes in precipitation are more likely to induce variability among basins (Fritz et al 2000), and that shortterm deviations among lakes likely reflect catchment-specific differences in how precipitation is exported to lakes from land (Blenckner 2005). However, because we also conclude that lakes of the Canadian Prairies are most strongly influenced by changes in winter precipitation, we suggest that long-term variations in lake chemistry and synchrony likely reflect major reorganizations in climate systems that regulate the transportation, persistence, and melting of winter precipitation (Michels et al 2007). Validation of these hypotheses is ongoing and requires first that we calibrate the isotopic signatures of lake sediments with the chemical and isotopic characteristics of overlying waters as has been done elsewhere (Huang et al 2004), and second, that we compare historical changes in isotope composition of sediments with independent metrics of past lake levels and salinity (e.g., diatoms; Fritz et al 2000).…”

“…7), and exhibited a pronounced surface lens of freshwater that had dissipated by midsummer. Although many prairie lakes are polymictic due to high area : depth ratios and high regional wind speed Pham et al 2008), strongly stratified meromictic lakes can also occur (Michels et al 2007; Table 1). We hypothesize that this subset of lakes may have exhibited highly complicated mixing of internal waters, which bias estimates of surface water isotope signatures during spring, but not at later times of the year.…”

“…Rather than varying coherently with each other as is commonly expected in most paleoclimate studies (e.g., comparisons with ice cores, tree-rings, etc. ), we anticipate that spatially structured but independent variation among lakes will provide key insights into historical changes in the climate systems which regulate winter precipitation (Michels et al 2007). …”

Interactive effects of chemical and biological controls on food-web composition in saline prairie lakes

“…According to global circulation models, future climate change will result in increased aridity across the Canadian prairies [75]. The ensuing warmer and drier climate will not only reduce freshwater inputs into the lakes but will also increase evaporation.…”

Drought Research in Canada: A Review

“…Recently, the finer sampling and more precise dating of lake sediments has yielded time series of higher resolution for the past several millennia. Diatom assemblages from Prairie lakes show multi-centennial shifts in the moisture regime (Laird et al, 2003;Michels et al, 2007). A marked shift from dry to moist conditions occurred around 800 years ago at Chauvin Lake and about 670 years ago at Humboldt Lake (both in the central Prairie region), coinciding with the end of the Medieval Climate Anomaly and the onset of the Little Ice Age.…”