CHANGES IN LAKE LEVEL AND PRODUCTION IN BOREAL SHIELD LAKES DURING THE HOLOCENE THERMAL MAXIMUM IN NORTHWEST ONTARIO

Sediment cores from three headwater lakes spanning 300 km gradient across the boreal region of northwest Ontario were investigated using pollen, diatoms and subfossil invertebrates over the Holocene period. Increases in non-arboreal pollen during the early to mid Holocene were longer and more pronounced closer to the forest-prairie boundary in comparison to sites located further into the boreal region. Nearshore sediment cores indicate that water levels were low in all lakes during the Holocene Thermal Maximum (HTM), with pronounced increases in water levels only during the last 4-5 thousand years. Algal and invertebrate remains in deep-central cores provide evidence of enhanced production of both algae and invertebrates during the HTM. These findings suggest that lakes in northwest Ontario are sensitive to changes in climate, and that consequences to future climate warming could include both declines in lake levels and increases in lake production.