Browsing by Subject "Hydroclimate"

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    Indicators of Euro-American land-use change as geochronologic markers in Midwest floodplain lake sediment archives
    (2024-02) LaRoche, Kierstin Marie; Bird, Broxton W.; Licht, Kathy J.; Gilhooly, William P., III
    In association with predicted rising global average temperatures, spring and winter precipitation in the Midwest is projected to increase by up to 30% by the end of this century. Enhanced by the alteration of natural environments, this increase will likely result in more frequent extreme flood events. To best prepare for these circumstances, interest has risen in reconstructing the dynamics between changing climate, altered landscapes, and fluvial systems with age-depth modeling, often using radiocarbon (14C) and 210Pb dating and multi-proxy evidence from floodplain lake sediment archives. Age- depth modeling over the last 300 years can be difficult, however, due to a large plateau in the radiocarbon calibration curve, and 210Pb dating is not reliable for all sediment records. Here, indicators of land-use change, magnetic susceptibility, Rb/Sr, Pb/Zr, and d15N values, were used to create age-depth control for Shannon Lake, IN, a difficult-to-date 600-year-old oxbow lake of the White River near Indianapolis. Age control for Shannon Lake was completed by correlating the timing in the rise of the same proxies from a previously well-dated lake record from Half Moon Pond, an oxbow lake of the White River near Petersburg, IN. The Shannon and Half Moon records were compared to those of three floodplain lake records of the Ohio River floodplain: Avery Lake, IL, Goose Pond, IN, and Grassy Pond, KY to investigate how these proxies varied in floodplain lake sediment from the lower Ohio River. The land-use indicators provided age-control for Shannon Lake, and the indicators of land-use change for the White River records resembled those of the Ohio River records over the last 600 years, where the onset of Euro-American land-use changes were detected at or around 1750 CE. MS, Rb/Sr, and d15N values displayed the greatest resemblance, while greater variations in Rb/Sr values were observed across the five lake records, potentially due to differences in regional setting or differences in the scale of the White River and Ohio River watersheds.
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    Midcontinental Hydroclimate Variability from a 1,500-yr Wisconsin Lake Sediment Record
    (2023-12) Nealy, Cameron Alexander; Bird, Braxton; Gilhooly, William, III; Licht, Kathy
    Lacustrine sediment archives preserve continuous records of changes in basin- to regional-scale processes that reflect broader variability in climatic conditions. Here, we present a 1,500-yr sediment record of inferred effective moisture (P/E) that spans the Current Warm Period (CWP; last 150 years), Medieval Climate Anomaly (MCA; ca. 950–1250 CE), and Little Ice Age (LIA; ca. 1300–1800 CE) from glacially-formed Pope Lake in central Wisconsin. A suite of sediment proxies constrained by 14C and 210Pb ages was developed at decadal resolution to investigate Common Era changes in Upper Midwest effective moisture in response to temperature and synoptic scale atmospheric variability, such as the Pacific North American (PNA) pattern. Lake water isotopes reconstructed with authigenic carbonate oxygen isotopes (d18Ocal) from Pope Lake compare favorably with other Midwestern closed-basin lakes, indicating that evaporation was a significant control on the isotopic composition of lake water. Relatively lower d18Ocal values during the MCA suggest that the moisture availability was greater during the MCA than LIA, despite increased air temperatures. This is supported by low carbon/nitrogen (C/N) ratios and low terrestrial lithic contributions that reflect increased lake levels during the MCA. Reversals of these trends during the cooler LIA were observed. Comparisons of the Pope Lake record to synoptic scale forcings suggest that shifts in regional P/E were consistent with high amplitude PNA variability that likely affected the source and seasonality of precipitation. The general warm/wet and cool/dry relationship noted during the MCA and LIA underscores how global temperature anomalies may alter the balance of effective moisture in the Upper Midwest in relatively short succession. The Pope Lake sediment record presented here is an important step in establishing hydroclimatic history that may inform expectations of future climate for a region sparsely populated with similar high resolution late Holocene records.