THE NEW NORTH AMERICAN VARVE CHRONOLOGY: A RECORD OF SOUTHEASTERN LAURENTIDE DEGLACIATION AND CLIMATE: 18.2-12.5 KYR BP

Long cores of glacial varves combined with records from surface exposures, and 43 radiocarbon ages, have allowed the correction, closure of a major gap, expansion, and calibration of Ernst Antevs’ (1922) original New England Varve Chronology in the Connecticut Valley of western New England. The varves were reformulated, with corrections and a new numbering system, as the North American Varve Chronology, a continuous 5659-yr sequence linked to and spanning most (18.2-12.5 kyr BP) of the last deglaciation in the northeastern US. A chronology of ice recession rates for separate intervals terminated by four stillstands and readvances of 1-2 century durations have been determined for the Connecticut Valley (from S to N): 50-100 m/yr in northern Connecticut; Chicopee Readvance; 30-40 m/yr in central Massachusetts; Hatfield event; 80-90 m/yr from Massachusetts to central NH; North Charlestown moraines; 300 m/yr to northern NH; Littleton Readvance; >100 m/yr to Canadian border. Ice recession is coupled to varve thickness that depicts changes in meltwater production and shows the relationship of changes in ablation rate (summer climate) to ice sheet activity and recession. Comparison of varve thickness records to the highest-resolution Greenland ice core climate records available (GISP2 δ¹⁸O original measurements) shows that from 15.0-12.5 kyr BP climate changes of decadal and longer scale recorded in both records appear identical in spacing and magnitude. Independent time scales for both records (varve ¹⁴C calibration and ice core layer counts) are different by 15 yr when similar features are matched between the two records. Varves and the Greenland ice cores appear to have synchronously recorded the same regional climate changes. After 15.0 yr BP, therefore, there was a link between North Atlantic climate and ice-marginal processes. Prior to 15.0 kyr BP, varve thickness varies with ice recession events but only very weak relationships between varve thickness and Greenland climate are evident. It appears that ice sheet changes during this time period were more subtle with the ice sheet in a state closer to equilibrium, and deglaciation may not have been dominated by a regional North Atlantic climate, perhaps responding more to ice dynamics or regional climate patterns centered elsewhere.