Sedimentary archives in lakes have been crucial for reconstructing climatic and hydrologic conditions of Earth’s past. The oxygen isotope records from skeletal materials are a key part of the toolkit for studying past climate with extensive use in marine and terrestrial settings including in lakes. For the Laurentide Great Lakes in North America, δ18O values (δ18Ocarb) of molluscs and ostracods (biogenic carbonates) have helped us understand their formation following the melting of the Laurentide Ice Sheet, subsequent isostatic rebound, and regional climate change over the past 15 ka. Biogenic carbonate δ18Ocarb values from Lake Erie, the shallowest of the Laurentide Great Lakes, have been critical for understanding its water balance, which is very sensitive to hydroclimate fluctuations. This works because δ18Ocarb values reflect the isotopic composition of lake water (δ18Olw), which is very sensitive to changes in lake evaporation or input sources. However, δ18Ocarb is a function of multiple hydrologic (temperature, humidity, evaporation, input sources) and isotopic levers (the isotopic composition of lake and atmosphere) which can significantly impact the δ18Ocarb value. In this dissertation, I demonstrate the advantages of evaluating the δ18Ocarb data in relation to regional water balance, lake configuration, and temperature constraints over the last 15 ka.

Chapter 2 characterizes the modern hydrological conditions of Lake Erie by evaluating the seasonal and temporal isotopic (δ18Olw, δ2Hlw, and δ’17Olw) variability of local precipitation, river, and lake water within the lake basin. Our results show a systematic variation in δ18Olwr, d-excess and Δ17Owater data of lake waters in relation to seasonal conditions and basin location. I then utilize the well-monitored hydrological system of the Great Lakes to constrain the fraction of moisture from the lake (f) parameter and the ratio of turbulent to diffusive fractionation (phi or n) parameter for Lake Erie. Both parameters are essential to the lake-water isotope mass balance models and significantly affect the isotopic composition of the water (δ18Owater) but are poorly constrained. I show initial studies constraints on f and phi are too restricted and I proposed an updated look at the variation in f and phi values.

Chapter 3 employs the isotope mass balance framework established in Chapter 2 for paleohydrology reconstructions of Lake Erie. I utilize biogenic carbonates from sediment cores from the eastern and western basin of Lake Erie to reconstruct the isotopic composition of formation water (δ18Ofw) in respect to changing lake configurations and temperatures over the last 15ka. This chapter reviews previous assumptions about lake hydrology in relation to input sources, lake evaporation, and basin dynamics and suggests that a water balance modeling approach can be used as an additional measure to constrain lake conditions. I demonstrate with mass balance modeling that Lake Erie was an evaporative lake during from ~15 to 10 ka, contrary to previous interpretations that Lake Erie was a high stand lake. After 10 ka, our mass balance approach supports previous interpretations suggesting that Lake Erie transitioned to a highly evaporative closed basin lake before shifting to its modern hydrology ~5ka.

Chapter 4 seeks to utilize micrite samples from the same sediment cores in Chapter 3 to evaluate whether lake micrite can reconstruct regional paleoclimate. Using x-ray diffraction (XRD), scanning electron microscopy (SEM), and clumped isotope geochemistry (Δ47), I analyzed samples for detrital contamination and whether these samples can be used to contextualize regional landscape changes in the Lake Erie basin. I find that all samples from the eastern and central basin have detrital contamination with reconstructed Δ47 temperatures ranging between 45 to 64°C. No micrite Δ47 temperature matches modern lake temperatures but matches previous Paleozoic and Mesozoic detrital limestone clasts Δ47 temperatures.

This dissertation represents a more extensive application of water balance modeling for paleoclimate applications and contributes abundant isotopic (δ18Olw, δ2Hlw, δ’17Olw, δ18Ocarb, δ13Ccarb, and Δ47) data for modern and paleo-lake systems. The data from this dissertation illuminates a strong connection between the water balance of Lake Erie, lake evaporation, and the Laurentide ice sheet both in the modern lake and paleohydrology.