Campbell, C. 2002. Late Holocene lake sedimentology and climate change in southern Alberta, Canada. Quaternary Research 49: 96-101.
What was done
The good correspondence typically observed between lake sediment grain size and historical climate fluctuations indicates that grain size varies with streamflow. Coarser grains correspond to moister climates and high streamflow, while finer grains correspond to drier climates and low streamflow. Based upon this relationship, the author analyzed the grain sizes of sediment cores obtained from Pine Lake, Alberta, Canada (52°N, 113.5°W) to provide a non-vegetation-based high-resolution record of climate variability for this part of North America over the past 4000 years.
What was learned
Periods of both increasing and decreasing grain size (moisture availability) were noted throughout the 4000-year record at decadal, centennial and millennial time scales. The most predominant departures included several-centuries-long epochs that corresponded to the Little Ice Age (about AD 1500-1900), the Medieval Warm Period (about AD 700-1300), the Dark Ages Cold Period (about BC 100 to AD 700) and the Roman Warm Period (about BC 900-100). In addition, a standardized median grain-size history revealed that the highest rates of stream discharge during the past 4000 years occurred during the Little Ice Age at approximately 300-350 years ago. During this time, grain sizes were about 2.5 standard deviations above the 4000-year mean. In contrast, the lowest rates of streamflow were observed around AD 1100, when median grain sizes were nearly 2 standard deviations below the 4000-year mean. Most recently, grain size over the past 150 years has generally remained above average.
What it means
The Pine Lake sediment record convincingly demonstrates the reality of the non-CO2-induced millennial-scale climatic oscillation that alternately brings several-century periods of dryness and wetness to the southern Alberta region of North America during concomitant periods of relative hemispheric warmth and coolness, respectively. It also demonstrates there is nothing unusual about the region's current moisture status, which suggests that the planet may still have a bit of warming to do before the Modern Warm Period is fully upon us.
Reviewed 8 January 2003