QUATERNARY RESEARCH 33, 219-230 (19%) Younger Dryas Climatic Reversal in Northeastern USA? AMS Ages for an Old Problem D. M. PETEET,* J. S. VOGEL,? D. E. NELSON,? J. R. SouTHoN,? R. J. NICKMANN,$ AND L. E. HEUSSERO *NASAlGoddard Space Flight Center, Institute for Space Studies, 2880 Broadway, New York, New York 10025; fDepartment of Archaeology, Simon Fraser University, Burnaby, British Columbia, Canada V5A lS6; SCarnegie Museum of Natural History, 44W Forbes Ave, Pittsburgh, Pennsylvania 15213; and OLamont-Doherty Geological Observatory, Palisades, New York 10964 Received November 28, 1988 Late-glacial macrofossils from a 10-m core from Alpine Swamp, New Jersey, were radiocarbon dated using accelerator mass spectrometry (AMS). The arrival of the first trees to the area fohow- ing deglaciation is indicated by maximum percentages of spruce pollen and a date of 12,290 2 440 yr B.P. on a single spruce needle. Subsequent spread of deciduous hardwoods was followed by the expansion of boreal taxa, including spruce (Picea), fir (Abies), larch (Larix laricina), paper birch (Betula papyrtfera), and alder (Alnus). Three AMS dates on paper birch seeds and a spruce needle during this boreal expansion indicate that it took place between 11,000 and 10,000 yr B.P. The timing of this vegetational shift and its correlation with late-glacial pollen stratigraphy from many sites in southern New England indicate that a climatic reversal correlative with the Younger Dryas characterized the North Atlantic seaboard of the United States. o 1990 Utiversity 0t wastington. INTRODUCTION Establishing the geographic distribution of specific climatic events is essential for understanding the mechanisms and causes of climatic change. The transition from the last glaciation to the present interglaciation is particularly intriguing because of an un- expected and dramatic return to cold con- ditions, which occurred even as Northern Hemisphere summer insolation increased (Berger, 1978). This Younger Dryas stade, approx ll,OOO-10,000 yr B.P., is clearly documented in data from Europe (Lowe et al., 1980; Watts, 1980), Greenland (Dans- gaard et al., 1982), eastern Canada (Mott et al., 1986a, b) and the North Atlantic (Rud- diman and McIntyre, 1981; Broecker et al., 1988). Correlations with cooling events in the mid-continental United States (Shane, 1987), southern South America (Heusser and Rabassa, 1987), the Antarctic (Jouzel et al., 1985), and the North Pacific (Mathewes, 1987; Keigwin and Jones, 1988) suggest a possible worldwide climatic event. Whether or not this climatic reversal is reflected by the pollen stratigraphy of southern New England has been debated for almost half a century. We discuss the reasons for this controversy concerning northeastern North America, including the following questions: (1) Is there a consis- tent pollen stratigraphy present in southern New England? (2) Does this pollen stratig- raphy indicate that a climatic reversal took place? (3) Is this reversal correlative with the Younger Dryas? We present new pol- len, macrofossil, and radiocarbon evidence from Alpine Swamp, New Jersey, that in- dicates that such a cooling indeed was ex- perienced in the northeastern United States. BACKGROUND Indications of a late-glacial climatic re- versal in the United States were first de- scribed about 50 years ago and reinforced by subsequent investigations (Deevey, 1939; Leopold, 1956; Deevey, 1958; Ogden, 1959). The typical southern New England 219 0033-5894&O $3.00 Copyrisbt 0 1990 by the University of Washington. Au rights of reproduction in any form reserved.