Holocene water levels at Rice Lake, Ontario, Canada: sediment, pollen and plant-macrofossil evidence

Abstract

Four cores taken along a transect from the western basin and four cores from the middle basin of Rice Lake, Ontario, provide evidence for shoreline transgression during the early Holocene, for low water levels during the mid-Holocene, and for abrupt rise of the lake levels due to dam building in AD 1838. The transition from detritus mud to the overlying marl, spanning from ca. 10000 to 8600 BP, indicates flooding of a wetland by a lake; this flooding is supported by plant-macrofossil succession from Larix, Scirpus, and Carex to Najas flexilis. The transgression was due to isostatic tilt after deglaciation, which raised the eastern outlet sill of the lake and caused the lake water to rise and flood westward. A sediment hiatus between the marl and the overlying gyttja (between 6000 and 4000-3000 BP) across the lake basin, supported by the bracketing radiocarbon dates and missing regional pollen zones, indicates low water level caused by a dry/warm climate. Regional palaeoclimatic estimates from pollen-climate transfer functions indicate that the mid-Holocene mean July temperatures were about 1°C higher and annual precipitations about 10% less than before or after. Subsequent rise of the lake level after the hiatus was a combination of cooling climate and continued isostatic tilt.