Holocene paleostorms identified by particle size signatures in lake sediments from the northeastern United States

摘要

The frequency and timing of Holocene paleofloods in the hilly terrain of New Hampshire and Maine are identified using C-14 and high-resolution (cm-by-cm) particle size analysis of sediment cores taken from six post-glacial lakes (similar to 0.1-1.4 km(2)). A total of nine sediment cores (4.5-6 m long) were taken near the base of stream delta foreslopes. End-member modeling of the particle-size frequency distributions from each core produces 3-5 representative end member distributions, or end members (EMs). Concurrent increases in mean and median particle size, and in the relative abundance of the coarsest EM(s), indicate increased transport capacity of inflowing tributaries, resulting from rainstorms. In all 9 cores, particle size data show clear signs of episodic, high-energy sediment transport events where proxy measurements such as loss-on-ignition and magnetic susceptibility do not, demonstrating the sensitivity of particle size analysis in paleostorm investigations made using lake sediment cores. Floods caused by storms in this region peaked around 1.4, 2.1, 3.0, 3.9, 6.8, 8.2, and 11.5 ka cal BP, and presently appear to be increasing in frequency. Periods of storminess in New Hampshire and Maine correlate well with other records of precipitation and climate in the northeastern United States during the Holocene, further supporting modern records which show tropical air masses as a primary driver of extreme precipitation events in New England (Ludlum 1996; Konrad 2001; Sisson and Gyakum 2004).