Lake Ontario’s sensitivity to climate- a Holocene perspective

Session: Large Lakes’ Response to Climate: Past, Present, and Future (2)

Francine McCarthy, Brock University, [email protected]
Abigail Burt, Ontario Geological Survery, [email protected]
John McAndrews, University of Toronto, [email protected]

Abstract

Palynological analysis of a well-dated continuously cored borehole from the Burlington Bar (Burt, 2017) illustrates the sensitivity of lake levels and water quality in Lake Ontario to climate change. Lewis and Todd (2018) presented evidence of marine incursion until isostatic rebound raised the outlet of Early Lake Ontario above the elevation of the Champlain Sea. By ~9.5ka, abundant desmids record fresh water, evidence of a positive water budget.  These palynomorphs recovered from mud overlying Halton diamicton in borehole BH94 record a quiet, shallow water environment.  About 10 m higher in the 65 m thick postglacial succession, sandy sediments rich in northern pine record initial bar formation of the during the cool, dry Early Holocene.  A hiatus in the pollen zonation is supported by radiocarbon ages ~8.2 ka and ~6ka bracketing gravel beds, correlating with the drought-induced late Stanley-Hough lowstand.  Bar formation resumed during the Middle Holocene when enhanced longshore drift is consistent with the moist conditions recorded by the pollen assemblage. Lake level fluctuations in the order of 2-3 m correlate with wetter intervals over the last 4000 years and fine-grained sediments in borehole BH94 correlate with periods of high lake level recorded in sediments from embayments like Grenadier Pond.