2006 Philadelphia Annual Meeting (22–25 October 2006)

Paper No. 6
Presentation Time: 9:25 AM


WILLARD, Debra A.1, BERNHARDT, Christopher E.1, BROOKS, Gregg R.2 and LARSON, Rebekka A.2, (1)US Geological Survey, 926A National Center, Reston, VA 20192, (2)Department of Marine Science, Eckerd College, St. Petersburg, FL 33711, dwillard@usgs.gov

We examine the timing and magnitude of floral change near Tampa Bay, Florida during the last deglaciation using radiocarbon-dated sediment core MD02-2579 that has decadal to sub-decadal temporal resolution between ~21 ka and ~11.4 ka. This core provides a record of subtropical ecosystem response to the Bölling/Allerød, Older Dryas, IntraAllerød Cold Period, and Younger Dryas climate events correlative with those from high- and low-latitude sites elsewhere in the Northern Hemisphere.

Between ~21 ka and ~17 ka, pollen assemblages indicate wetland habitats, primarily fed by groundwater, during an interval of reduced precipitation relative to today. Abundant Carya (hickory) pollen during this interval indicates persistence of winter temperatures 3˚ to 4˚ C cooler than today. The initial deglaciation began ~17.1 ka and is marked by increased abundance of Pinus (pine) pollen and a shift to lacustrine conditions. Throughout the Bölling/Allerød interstadials (14.7 – 12.9 ka), Pinus pollen reached nearly modern levels, but several centennial-scale peaks in abundance of Chenopodiaceae/Amaranthaceae (pigweeds, water hemp) pollen occur throughout the deglaciation: ~14.9 ka (Oldest Dryas), ~14.1 ka (Older Dryas), ~13.7 ka, and ~13.1 ka (IntraAllerød Cold Period). The Younger Dryas stadial (12.9 – 11.4 ka) also is characterized by high percentages of Chenopodiaceae/Amaranthaceae pollen and increased organic content of sediments consistent with expansion of wetland habitats.

Our results indicate: 1) the deglacial warming began ~17 ka, accompanied by increased precipitation; 2) further warming and increased precipitation occurred during the Bölling/Allerød interstadials; and 3) rapid shifts to drier conditions during the Younger Dryas and other stadials are in phase with other high- and low-latitude paleoclimate records from the Northern Hemisphere.