24-20 Quantifying the Relationship Between Sediment Composition and Water Depth at Norman’s Pond, Newfoundland to Develop a Holocene Record of Water Level Fluctuations

Session: Lake Sedimentary Records of Past Climate and Environment (Posters)

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Abstract:

A severe drought in Newfoundland, Canada during the summer of 2025 highlighted the vulnerability of regional water resources. Impacts of this event included reduced reservoir and lake water levels, water use restrictions, stress on aquatic ecosystems, and challenges for both urban and rural, subsistence communities. This event emphasizes the need to place recent climate changes within a longer-term context, to better understand natural variations in drought frequency and severity. However, the instrumental record of climate for Atlantic Canada is relatively short, and regional paleoclimate records that document drought are limited in number and temporal coverage. Here we develop a record of water level fluctuations from Norman's Pond, a relatively small and shallow carbonate lake, located in western Newfoundland (48.891° N; 57.912° W; 265 m ASL). We collected sediment cores and surface sediments along a littoral to profundal transect, characterized the composition of sediments, and constrained facies changes using radiocarbon dates on terrestrial macrofossils. A water column profile was established in the central depocenter of the lake to evaluate the degree of stratification in the lake. Compositional analysis of modern surface sediments indicate carbonate sediments dominant in shallow water above the modern thermocline of 6-7 meters and increasingly organic-calcareous sediment deposits in deep water. These observations are generally consistent with the Carbon Pump Hypothesis explaining carbon cycling in lakes, resulting in an inverse relationship between sediment carbonate content and water depth. Results from an intermediate water depth core site shows deglaciation by 10.2 thousand calendar years before CE 1950 (ka BP), an interval of organic sediment and inferred high lake levels and wet conditions from 10.2-5.0 ka, and a subsequent shift to finely layered carbonate sediments and inferred low lake levels and dry conditions from 5.0 ka to present. Additional radiocarbon dates will constrain similar stratigraphic changes in shallow and deep water cores, and all data will be synthesized to generate a quantitative lake level curve. We will evaluate the Norman’s Pond data in the context of other regional paleoclimate datasets and records of external forcing, to better understand the underlying controls on variations in Holocene drought frequency and severity.

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