From Lake to Fen: A Record of Holocene Climate Change at Kampoosa Bog, Stockbridge, Massachusetts

Sediment from Kampoosa Bog records 13,000 years of climate history as it evolved from a glacial lake to calcareous fen. The lower 1.55 m of an 8.84 m core contain varved clays from a large glacial lake that occupied the Housatonic River Valley near Stockbridge MA. Radiocarbon (AMS) dates and Loss on Ignition (LOI) data from the 8.84 m core show that sedimentation rates were initially high from 13,000-11,000 ybp during the glacial lake phase (16.25 mm/y) as clastic varves accumulated, then decreased as the glacial lake drained leaving a small residual lake in the area of Kampoosa Bog. After 11,000 ybp the residual lake was slowly filled (0.40 mm/y) by mainly organic material during a warm period during which organic carbon concentrations increased from less than 10% to 82%. The region experienced a cool, dry period with low lake levels from 10,000 ybp to 6,000 ybp, as organic carbon concentrations decreased to less than 30% and inorganic carbon concentrations increased from 5% to 30%. At this time there is a strong linear correlation between organic and inorganic carbon concentrations that may reflect the metabolic conversion of organic carbon to inorganic carbon by fossil organisms. Within this section of the core, there was an abundance of fossils of gastropods and bivalves. After 7,500 ybp, the sedimentation rate increased from 0.40 mm/y to 0.71 mm/y and by 6,000 ybp, gastropods and bivalves were no longer present, marking an abrupt end to the cool, dry period. After 6,000 ybp, lake level rose and temperatures warmed until the Holocene Thermal Maximum at about 2,000 ybp when the lake transitioned to a calcareous fen and sedimentation rates increased to 0.95 mm/y.