Abstract:
Following the 1997 Red River flood, a program of research was initiated to determine how large the floods can be, how often large floods have occurred in recent centuries, and whether natural factors may be changing the flood risk. As part of this program, 15 cores were collected from the south basin of Lake Winnipeg. Paleomagnetic profiles were used to select three apparently undisturbed, high-sedimentation rate cores for detailed chemical, physical, and biological
analyses, to assess whether Red River floods are recognizable in the lake. A thousand-year paleomagnetic chronology was confirmed and augmented by Cs-137, Pb-210, palynology, radiocarbon dating, and inorganic geochemical relative age markers. While some parameters exhibit multi-century fluctuations, varying excursions, and 20th century shifts, grain-size results show the clearest signal of recurring events. Several layers of enhanced silt, 1-4 cm thick, with 6-15 % more silt than background are present, in several cases correlating core to core. A Red River flood origin for these silt excursions is plausible. The results also provide indications of increased contamination, nutrient influx, and more rapid sedimentation in the 20th century.
