THE NEW NORTH AMERICAN VARVE CHRONOLOGY: A PRECISE RECORD OF SOUTHEASTERN LAURENTIDE ICE SHEET DEGLACIATION AND CLIMATE, 18.2-12.5 KYR BP, ANDCORRELATIONS WITH GREENLAND ICE CORE RECORDS

摘要

New glacial varve records from long cores combined with records from key surface exposures and new radiocarbon ages have allowed the correction, consolidation, expansion, and calibration of Ernst Antevs' original New England Varve Chronology (NEVC) in the Connecticut Valley of New England, U.S.A. The varve records have been reformulated, with corrections and a new numbering system, as the new North American Varve Chronology (NAVC), which is a continuous 5659-yr varve sequence that spans most of the last deglaciation (18,200-12,500 yr BP) in the northeastern United States. Rates of ice recession for separate intervals terminated by abrupt glacial stillstands and readvances have been determined for western New England. Ice recession history is coupled to varve thickness changes that depict changes in meltwater production in the Connecticut Valley and show the relationship of changes in ablation rate (summer climate variation) to glacial readvances and periods of halted and rapid ice recession (up to 300 m/yr). Comparison of varve thickness records to Greenland ice-core climate records show that after 15,000 yr BP, climate changes of sub-century and longer scales recorded in both records appear identical and synchronous. After 15,000 yr BP, therefore, there was a link between North Adantic climate and marginal processes of the southeastern sector of the Laurentide Ice Sheet (LIS). Prior to 15,000 yr BP, when the LIS was closer to an equilibrium condition, retreat rates were generally lower and changes in varve thickness and ablation were more subtle, but can still be linked to ice sheet activity. Only weak relationships between varve thickness changes and Greenland climate are evident suggesting that changes in the southeastern LIS during this time may have been significantly influenced by climate patterns unique to the North American continent or ice dynamics.