Late-Glacial to Early Holocene Climate Changes from a Central Appalachian Pollen and Macrofossil Record

Abstract

A late-glacial to early Holocene record of pollen, plant macrofossils, and charcoal has been obtained from two cores from Browns Pond in the central Appalachians of Virginia. An AMS radiocarbon chronology defines the timing of moist and cold excursions, superimposed on the overall warming trend from 14,200 to 750014C yr B.P. This site had cold, moist conditions from ca. 14,200 to 12,70014C yr B.P., with warming at 12,730, 11,280, and 10,05014C yr B.P. A decrease in deciduous broad-leaved tree taxa andPinus strobus(haploxylon) pollen, simultaneous with a reexpansion ofAbies,denotes a brief, cold reversal from 12,260 to 12,20014C yr B.P. A second cold reversal, inferred from increases in montane conifers, is centered at 750014C yr B.P. The cold reversals at Browns Pond may be synchronous with climate change in Greenland and northwestern Europe. Warming at 11,28014C yr B.P. shows the complexity of regional climate responses during the Younger Dryas chronozone.

Ecosystem response to Lateglacial and early Holocene climate oscillations in the Great Lakes region of North America

“…The regional variations in evidence for the YD event as summarized above suggest that the YD likely has di!erent expressions in paleoecological records depending on geographic location and character of a particular site. In some regions, the YD event may not be expressed as a cold interval (see An et al, 1993;Roberts et al, 1993;Kneller and Peteet, 1999). The YD climatic reversal may also appear to be time-transgressive if su$cient sites are available with reliable dating control (Cwynar and Levesque, 1995).…”

Sensitivity and rapidity of vegetational response to abrupt climate change

“…The best examples of abrupt climate change recorded by vegetational records suggest that, where a sharp ecotone exists, the pollen͞macrofossil records provide a sensitive and rapid response to a climate change. This is true of records in southern New England and the southern Appalachians, where a mixture of boreal and deciduous species during the late-glacial provided the mixture of species for immediate response to a temperature changeeither a rapid decrease (YD, 8,200-yr event) or a rapid warming (Holocene change) that occurred within a century (6,(15)(16)(17)(18). This rapid response to the Holocene warming is also seen in coastal Alaska, where cold, windswept tundra is rapidly replaced by tundra species that favor moisture and warmth (24).…”

“…This same pattern of abrupt shifts in climate is seen in great detail in the Greenland oxygen isotope pattern (1). Some recent papers highlighting the pattern of abrupt late-glacial climatic shifts in sediment records as similar to this Greenland pattern include the European pollen, beetle, and isotopic lake records (2), midge (chironomid) larvae response to lake water temperatures estimates in maritime Canada (3), shifts in stable isotopes in central North America (4), antiphasing between rainfall in North America's Great Basin and Africa's Rift Valley (5), and patterns of vegetation response in the central Appalachians (6). These terrestrial patterns of shifts parallel marine records from the North Atlantic (7) and the tropical Atlantic (8).…”

Post-glacial evolution of Panicum virgatum: centers of diversity and gene pools revealed by SSR markers and cpDNA sequences

“…Although little is known about genetic diversity, spatial differentiation, genetic isolation, or post-glacial migratory patterns of switchgrass, a general pattern has emerged, particularly with reference to woody species. Fossil pollen records from lakebed sediments have revealed a pattern of post-glacial northward migrations for dominant species of boreal and temperate forest ecosystems as well as prairie and savanna ecosystems (Clark et al 2001;Kelley et al 2006;Kneller and Peteet 1999;Soltis et al 1997). Genetic diversity decreases markedly for both plant and animal species on a north-south axis in both North America and Europe, suggesting that post-glacial founder effects have significantly reduced genetic variation in northern populations of species that have a large latitudinal distribution (Hewitt 1996(Hewitt , 2000Soltis et al 1997).…”