Midcontinental hydroclimate variability from a 1500-yr Wisconsin lake sediment record, USA

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 1500-year sediment record of effective moisture (precipitation/evaporation; P/E) from glacially-formed Pope Lake in central Wisconsin that spans much of the Common Era (CE; i.e., the last 2 kyr), including the Current Warm Period (CWP; last 150 years), Medieval Climate Anomaly (MCA; ca. 950–1250 CE), and Little Ice Age (LIA; ca. 1400–1700 CE). A suite of sediment proxies constrained by ¹⁴C and ²¹⁰Pb ages were analyzed at decadal resolution to investigate Common Era changes in Upper Midwest effective moisture in response to temperature and synoptic scale atmospheric variability. Lake water isotopes reconstructed using authigenic carbonate oxygen isotopes (δ¹⁸O_cal) from Pope Lake covary with results from other Midwestern closed-basin lakes, indicating that P/E was a significant control on the isotopic composition of lake water. Relatively lower δ¹⁸O_cal 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 were observed during the cooler LIA. Comparisons of the Pope Lake record to synoptic scale forcings, such as the Pacific North American (PNA) pattern, suggest that shifts in regional P/E were consistent with high amplitude PNA-like variability that likely affected the source and seasonality of precipitation. The general warm/wet and cool/dry relationships respectively noted during the MCA and LIA underscore 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 toward reconstructing the region's hydroclimatic history and may inform expectations of near-future climate variability in a region with few Late Holocene records of comparable length or resolution.