Tracking Long-Term Changes in Climate Using Algal Indicators in Lake Sediments (original) (raw)
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Quaternary Science Reviews, 2007
Paleoclimatic records from the climatically sensitive Canadian prairies are relatively rare due to the scarcity of study sites with continuous Holocene stratigraphic sequences. Oro Lake, a meromictic lake in the dry grasslands of Saskatchewan (Canada), contains a continuous Holocene diatom record spanning the last ˜10,000 years. Here we present analyses at three different time scales and resolution: (1) 1 3 yr resolution of the past ˜80 years, (2) century-scale analysis of the Holocene, and (3) decadal-scale analysis of the past ˜7000 years. Recent changes in the diatom assemblages and their respective salinity inferences were significantly related to measured effective moisture (precipitation minus evaporation, P-ET). The droughts of the 1930s, and a wet period during the 1950s are clearly evident in the diatom record, suggesting the Oro Lake record contains a sensitive archive of past climatic conditions. Century-scale analysis of the diatom record during the Holocene is consistent with a cool and moist climate in the early Holocene (prior to ca 9700 cal yr BP, 8600 14C yr BP). An abrupt increase in diatom-inferred salinity at 9600 cal yr BP (8500 14C yr BP) indicates the onset of an arid climate, with continuing arid conditions throughout the mid-Holocene. Decadal-scale analysis of the past ˜7000 years suggests that the mid-Holocene was more complex, with extended periods of increased variability in precipitation, particularly between ca 5800 3600 cal yr BP (5000 3200 14C yr BP) which is characterized by intervals of increased effective moisture. The past ˜2000 years is characterized by reduced salinities and generally wetter conditions in comparison to the mid-Holocene. The combination of the different scales of analyses in this study provides a detailed account of the dynamic nature of climate from sub-decadal to millennial scale in the Oro Lake region within the Palliser Triangle. Climate model predictions suggest that the Canadian prairie region may see a higher frequency of extreme droughts under projected global warming, potentially similar to the most arid periods seen during the mid-Holocene when many lake basins completely dried out.
Approaches to Holocene climate reconstruction using diatoms
Global Change in the Holocene, 2003
Diatom analysis has been used extensively to reconstruct past environments, and increasingly attention is being given to developing the technique to model Holocene climate variability. This chapter reviews progress in the field, including both qualitative and quantitative interpretations: (i) the relationships between diatoms and climate indicators such as solar insolation (Elk Lake, Minnesota), snow cover (Lake Baikal) and ice cover (Elison Lake, Ellesmere Island); (ii) the development of models to reconstruct diatom inferred climates, either directly (e.g. surface water temperature, Scandanavia) or indirectly (e.g. pH in the Austrian Alps and on Baffin Island; e.g. salinity in lakes in the Northern Great Plains region, North America); and (iii) the development of high resolution studies in coastal and marine environments (including the Icelandic Shelf, the Antarctic Peninsula and the eastern Norwegian Sea). The importance of autecological and taphonomic studies is highlighted, although they still receive too little attention when attempts are made to interpret past climates using diatom analysis.