USING MACROFOSSILS TO RECONSTRUCT PRECIPITATION PATTERNS IN THE LATE PLEISTOCENE/EARLY HOLOCENE

Two of the biggest threats of rapid climate change facing society today are accelerated sea level rise and changes in precipitation patterns that will result in alterations to global water distribution. Proxy data have been used to reconstruct rates of sea level rise and ecosystem changes related to climate change. Macrofossil plant assemblages allow not only comparison of the vegetation response to temperature but also have potential to be used to characterize precipitation patterns within a local or regional area.

The late Pleistocene was a period punctuated by rapid climate fluctuations in both the Polar Regions and to a lesser extent in the temperate regions. Macrofossil assemblages extracted from vibracores taken from the Great Swamp in South Kingstown, RI as well as other regional proxy data were compared with δ¹⁸O record from the GISP2 ice core to correlate temperature changes in the polar region with landscape wide changes in southern New England. One vibracore was located at the wetland/upland transition and likely to be more sensitive to precipitation changes than cores within the central swamp. The macrofossil record from this location indicated that the environment transitioned from shallow open water to emergent wetland coincident with a rapid temperature rise in Greenland (~14700 calendar years BP). As the climate cooled, the area reverted back to shallow open water, followed by a widely fluctuating water table prior to the Younger Dryas. Water levels stabilized in the Younger Dryas when a scrub/shrub swamp or fen developed at this location as a result of more consistent precipitation combined with other factors such as decreased evapotranspiration rates. Extensive fluctuation in the water table predominated at the Holocene transition.

Ecosystem changes at the Great Swamp caused by changes in the water regime point to reduced precipitation in southern New England during warmer polar temperature oscillations and more consistent rainfall patterns during cold polar temperature oscillations in the late Pleistocene. Periods of flux between warm to cold and cold to warm were also times when precipitation patterns alternated between flooding and drought. These late Pleistocene environmental changes may offer a glimpse into impacts from weather extremes that are occurring now and will continue into the future.