EARLY HOLOCENE DROUGHT IN THE LOWER GREAT LAKES?

Since the 8200 year event was first documented in GISP 2 ice core from Greenland, signals for the event have been recognized globally. No comprehensive study of the impact of this event has been made in the Great Lakes region, however.

Drier, more continental conditions are evident from the regional pine zone found throughout northeastern North America during the early Holocene, and recent work in Georgian Bay has identified evidence for closed basin conditions during the Hough Lowstand, which appear to correlate with the 8200 year event. Brackish conditions recorded by Centropyxis- dominated thecamoebian assemblages, associated with drowned beaches and in situ stumps of cedar and tamarack suggest climate drove Georgian Bay to closed basin status once meltwater was largely diverted from the Great Lakes. The establishment of a Boreal Parkland biome just northeast of North Bay at this time suggests that the anticyclonic winds associated with the decaying Laurentide Ice Sheet produced a negative water budget in the Georgian Bay basin.

Despite the abundance of paleoecological studies published from the Lower Great Lakes, there is little evidence of aridity during the early Holocene. This suggests either that paleoecologists failed to properly interpret evidence of greater aridity, or that climate in the Lower Great Lakes basin was less arid than that in the Georgian Bay basin, the distance from the ice front being much greater, and the proximity to warm, moist air from the Gulf of Mexico also being greater. Our investigations to date suggest a combination of the two factors: there is some indication of increased aridity and alkalinity in wetland and lacustrine records from the Niagara Region, but the impact of the 8200 year event on this region does appear to be more muted than the impact on Georgian Bay.