Multi-proxy approach to long- and short-term Holocene climate-change: evidence from eastern Lake Ontario

We use a multi-proxy (n = 11) paleolimnological approach on deep-water sediment from eastern Lake Ontario to characterize both long- and short-term regional climate change over the past similar to 10,000 calendar years. Proxies included % total organic matter, % total carbonate, magnetic susceptibility, C/N ratios, % organic carbon, % total nitrogen, % biogenic silica and delta(18)O and delta(13)C of carbonate, as well as delta(13)C and delta(15)N of bulk organic matter. There is a marked shift in most proxies at similar to 9.4 ka which defines the start of Holocene warmth in this region. Prior to this, the area was influenced by the post-Younger Dryas cold/wet interval, controlled by a southward displacement of the polar front jet stream, when many proxies were at their minimum. The Hypsithermal interval (similar to 9.4 - 5.3 ka) was the warmest and wettest of the Holocene due to a long- term increase in summer insolation. The Hypsithermal, however, was interrupted by two cold climates; the 8.2 ka event (similar to 8.4 - 8.0 ka) and the Nipissing Rise (similar to 6.8 - 5.0 ka), both of which are linked to a reduction in thermohaline circulation and northward oceanic heat transport. The Neoglacial interval (similar to 5.3 ka to similar to 1850 AD), driven by a long- term decrease in summer insolation, was cooler and dryer, but more stable, than the Hypsithermal. The short Historic interval (post similar to 1850 AD) was characterized by some of the largest amplitude and most abrupt anomalies of the past 10,000 years, due to intense anthropogenic activity, when a number of proxies reached unprecedented values.