HYPOXIA AND CLIMATE CONDITION OF THE CENTRAL BASIN OF LAKE ERIE, NORTH AMERICA: INSIGHTS FROM GEOCHEMISTRY, OSTRACOD, AND POLLEN RECORDS DURING THE HOLOCENE

An analysis of a 10 m long sediment core (84a) collected from Lake Erie’s Central basin was conducted to understand the climate and hydrological controls on the development of summer bottom water hypoxia (low oxygen) over thousands of years. This analysis was done by generating new data on the presence and species abundance of ostracod (seed shrimp) shells separated from the sediment. It complements geochemical and sediment property data previously generated from the core by students at CWRU, Kent State University, and the University of Akron that showed a 2-step decrease of carbonate mineral abundance in the sediment between 5000 and 3000 years ago. This project was undertaken to test the hypothesis that the carbonate mineral loss records the origin and evolution of a low-pH, and low-oxygen layer of bottom water due to the development of seasonal thermal stratification. This work documented diverse ostracod species below the lower of the two carbonate shifts, including Candona Subtriangulata, which requires well oxygenated waters. This work did not find ostracods above the shift, possibly attributable to lower abundance and small sample size. Comparison of the geochemical data (CaO) to shorter cores studied by L.D. Delorme (1982) shows that ostracods between the two carbonate shifts are limited to species that are tolerant of low oxygen conditions. Neither study found ostracods above the second shift in the youngest sediments of the cores. The absence of their shells is attributed to carbonate dissolution in low pH waters because live ostracods have been found in the central basin today, but their shells are not preserved. Additionally, the distribution of pollen was analyzed in core 84, with preliminary data indicating stratigraphic changes in abundance and type. These findings highlight the need for further analysis of pollen distribution to aid in understanding links between oxygen deficiency, hydrologic changes, and climate in the Great Lakes region. Knowing more about the presence of these conditions in Lake Erie’s Central Basin is essential for ensuring the maintenance of its ecological diversity, water quality, and overall health, all of which are significantly valued and depended on by millions of people and many Ohio economies.