Major shifts in diatom community structure suggest circa 1900 CE response to climate change in boreal lakes from NW Ontario, Canada

Wiltse B & Cumming BF. 2009. Major shifts in diatom community structure suggest circa 1900 CE response to climate change in boreal lakes from NW Ontario, Canada. 11th International Paleolimnology Symposium, International Paleolimnology Association, Guadalajara, Mexico.

Various studies throughout North America have shown that ice-free periods of lakes are increasing.  These changes have largely been attributed to a warming climate in these regions.  The IPCC predicts this warming will be at a higher rate in North America than the rest of the world.  It has been suggested that the greatest degree of warming will be observed during the winter months, and that the snow and ice season will decrease with time.  This trend has in fact been observed across North America and is particularly well documented at the Experimental Lakes Area (ELA).  At ELA the duration of the ice-free season has increased in the main reference lake, Lake 239, by 2 weeks since 1969, with earlier ice off accounting for 64% of the change.  This winter warming and extended ice-free season is believed to be the cause of large increases in planktonic diatoms over the past century at ELA.  A similar trend has been observed in arctic lakes where warming is of a much higher magnitude.  The most notable change has been an increase in planktonic taxa C. stelligera in many lakes. Previous work has shown widespread increases of C. stelligera in over 20 ELA lakes, suggesting a regional forcing factor.  In this study we have looked at four lakes at ELA in much greater detail than previous studies.  Sediment cores from these lakes were analyzed for changes in diatom community structure and dated using 210Pb radioisotopes.  All four lakes showed a notable and apparently synchronous shift in the diatom community towards more planktonic forms; particularly C. stelligera.  The timing of this shift occurred in the early 1900s for all four lakes, suggesting that small temperate lakes may be more sensitive to recent climate change than previously believed.