New ages for shoreline stumps along Lake Winnipeg, Canada, and their implications for paleo-lake level estimates

As the largest body of water on the northern Great Plains of North America, Lake Winnipeg in central Manitoba, Canada, is crucial to the region’s hydrology, economy, and society. Previous research identified exposed subfossil stumps at several locations along the shore in both the lake’s north and south basins, and interpreted them as evidence of low lake levels c. ad 1650 caused in part by reduced inflows. Here, we report new radiocarbon dates for submerged stumps rooted in the foreshore of Lake Winnipeg near the Spider Islands, which are located in the lake’s northeastern sector close to its outlet. The 11 stumps had calibrated ages ranging between 2880 and 4150 cal. yr BP, which implies the establishment and mortality of these trees had no connection to Lake Winnipeg and instead that they grew, died, and were preserved within a forest located several hundreds of meters inland. If these new dates are correct, they argue against a simple hydrological explanation for these submerged trees. Instead, our results suggest these trees died 3–4 kyr ago and are now exposed because of gradual, isostatically driven changes in the basin configuration and shoreline position of Lake Winnipeg. Because they date to the mid- or late Holocene, we conclude these subfossil stumps do not constitute clear evidence of hydrologically caused low lake stands in Lake Winnipeg or widespread drought on the northern Great Plains.