Abstract
We evaluated relative levels of paleo‐primary productivity in eastern Lake Ontario during the past ~10,000 yr via analysis of inorganic and organic sediment from the Rochester Basin. There was significant natural variability in primary production correlative with Holocene climate change. The cold post‐Younger Dryas interval (~10–9.4 ka) was a time of minimal levels of primary production. The warm Holocene Hypsithermal interval (~9.4–5.3 ka) had much higher levels of primary production but was more variable, including five well‐defined cycles that have an average period of ~750 yr. The largest negative anomaly in primary productivity occurred during the 8.2‐ka climate event (~8.4–8.0 ka), a time of cold, dry conditions. Another negative anomaly occurred in association with the Nipissing flood (~6.3–5.3 ka), which triggered a regional cooling event. The cool Holocene Neoglacial interval (~5.3 ka to ~1850 A.D.) was characterized by lower, but more stable, levels of primary production, as well as by a cessation of calcite precipitation and the onset of diatom productivity. During the historic interval (~1850–1940 A.D.), there was a dramatic increase in primary production to unprecedented levels over the past 10,000 yr, as well as a 30–fold increase in sediment accumulation rates. These large, abrupt changes occurred in response to regional deforestation, anthropogenic nutrient loading, and increased chemical weathering due to acid rain. We project that, during 21st century global warming, eastern Lake Ontario will evolve into an ecosystem similar to that during the Holocene Hypsithermal.