ENVIRONMENTAL SYSTEM TRANSITION AT THE MID-HOLOCENE HYPSITHERMAL: EVIDENCE FROM THE SEDIMENT OF SENECA LAKE, NY

The Finger Lakes region of the northeastern United States experienced a dynamic climatic transition near the mid-Holocene hypsithermal. Erosional truncation of early Holocene strata within Seneca Lake, as indicated by high-resolution (2-12 kHz) seismic profiling and stratigraphic correlation of magnetic susceptibility, carbonate, water content, and total organic carbon analyses of six 2 to 3-m piston cores supports such an environmental transition.

A seismic profile delineated map of Holocene sediment thickness aided in the selection of sites for recovery of piston cores. To assess the relative truncation of early and late Holocene sections, these cores were described and analyzed along the length of the Holocene section. Magnetic susceptibility measurements were taken every 2 to 3-cm downcore, and samples for water content, bulk calcite content, and total organic carbon (TOC) analyses were obtained at approximately the same sampling interval.

Results indicate that early Holocene sedimentary sections are truncated predominantly more than late Holocene sedimentary sections. Such selective truncation of early Holocene sediment suggests that atmospheric circulation, as well as the greater environmental system, became more dynamic in the Finger Lakes region of the northeastern United States at the mid-Holocene, possibly in relation to cooler surface air temperatures and an associated southward shift in the jet stream.

Stratigraphic correlation of calcite profiles to three established and dated intervals of the early Holocene, suggests that climate abruptly changed after or near the hypsithermal and effectively created a gap in the sedimentary column representing ~7-8.5 ky in the shallowest cores.