Vegetation south of the ice margin in eastern North America during the last glacial maximum and deglaciation

Background/Question/Methods

Knowledge of late Quaternary vegetation dynamics of the unglaciated southeastern United States remains murky, owing to paucity of paleoecological sites and uncertainties in age-estimation for sites that have been studied.   Inadequate knowledge of this period hampers understanding of the ecological and biogeographic consequences of climatic changes of the past 25,000 years, and of the nature and mechanisms underlying the “no-analog” vegetation that occupied much of this region during the late-glacial.  To address these uncertainties, we obtained new cores from three previously studied sites in the region:  Anderson Pond (central Tennessee), Jackson Pond (central Kentucky), and Cupola Pond (south-central Missouri).  We report new pollen and plant macrofossil sequences tied to AMS-dated sediment chronologies from these sites.

Results/Conclusions

All three sites have basal sediments dating 22,000 to ca. 30,000 cal-yr BP, and all have continuous records spanning the last glacial maximum (LGM; ca. 21,000 yr BP) and initial post-glacial warming.  The Jackson Pond record is truncated by a depositional hiatus ca. 16,000 yr BP, and the Anderson Pond record has a hiatus ca. 13,000 yr BP.  Deposition at Cupola Pond continued until at least 11,000 yr BP.  The late-glacial to Holocene transition is missing from all the sites, as is most of the Holocene.  Pollen assemblages before and during LGM at all three sites are overwhelmingly dominated by Pinus and Picea; macrofossils confirm local occurrence of Picea and Pinus banksiana at all three sites.  All three sites show evidence of warming commencing shortly after LGM, marked by modest increases in Quercus pollen commencing between 20,000 and 18,000 yr BP.  “No-analog” pollen assemblages, characterized by Picea, Quercus, Fraxinus, Ostrya-type, Ulmus, and Carya, commence at Anderson Pond ca. 16,000 yr BP, and continue until the hiatus at ca. 13,000 yr BP.  They are absent from our Jackson Pond record, evidently postdating the hiatus in our core.  No-analog assemblages characterized by Picea, Quercus, and Fraxinus develop at Cupola Pond by 16,000 yr BP.  They are rapidly replaced by a new no-analog assemblage, dominated by Picea, Quercus, Ostrya-type, Carya, and Ambrosia ca. 14,500 yr BP.  Sporormiella spores are rare throughout the record at all our sites, in contrast to sites in glaciated terrain to the north (e.g., Appleman Lake, IN; Silver Lake, OH).  This contrast may indicate differences in depositional setting, in megafaunal populations, or megafaunal activity on the regional landscape.