Postglacial development of a Maine bog and paleoenvironmental implications

Abstract

Stratigraphic data on gross peat components, plant macrofossils, pollen, ash after ignition, and radiocarbon ages are used to reconstruct the developmental history of the north unit of Caribou Bog in central Maine, which presently consists of a sparsely wooded, ombrotrophic (raised), center surrounded by extensive wooded fen. A lake existed from 12 500 to 8500 BP, when terrestrialization led to peatland initiation throughout the basin within ~500 years. Near the center of the present peatland, limnic sedge fen developed to sedge fen at 8000 BP, and to Larix laricina wooded fen at 7000 BP. At 5500 BP the wooded fen became Sphagnum dominated and sparsely wooded, a condition that has persisted at the peatland center. Only two early transitions are clearly related to climate forcing. An abrupt shift from silt–clay to organic lake sediment ~10 400 BP is typical of basins throughout the region. This shift correlates with rapid changes in local and regional vegetation, and likely reflects increased biological productivity caused by a rapid warming of climate. Peatland initiation 8500–8000 BP coincides with a drop of water level, probably associated with a rapid shift to drier climate. We estimate that the water level around the peatland was at least 0.4 m above the present level at and before 8500 BP, dropped at least 1.7 m (min. 1.4 m with correction for peat compaction) in the next 500 years, and rose to the present level around 7000 BP or later. Major hydroseral changes after 8000 BP are asynchronous at several coring sites and are not consistently correlated with regional paleoclimatic events. These changes were probably induced by autogenic hydrological processes associated with peat accumulation. Key words: wetland history, paleoclimate and paleohydrology, pollen, plant macrofossils, peat stratigraphy, Maine.