PARENT SESSION
Poster Session #22: Paleoecology.
Wednesday, August 8, 2001. Presentation from 10:30 AM to 12:00 PM. Exhibition Hall
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Mid-Holocene northern Minnesota lake sediment record suggests global warming induced landscape changes.
SANFORD, PATRICIA1, WINKLER, MARJORIE1, 1
ABSTRACT- The middle Holocene record of Cayou Lake (Voyageurs National Park) in northern Minnesota was examined for changes that might be relevant for predicting landscape changes from greenhouse gas-induced global warming. A sediment core was analyzed for pollen, diatoms, cladocera, charcoal, sediment chemistry, and sediment carbon isotopes. The middle Holocene appeared to be divided into two periods: 8000-6000 yr B. P. which was warm and dry and 6000-4000 yr B. P. which was warm and wet. From 8000-6000 yr B. P. grass, ragweed and other composites, and other herb pollen, non-siliceous algae, and carbonate increased. An increase in littoral diatoms indicated a slight shallowing of the lake. New limnetic cladoceran species entered the lake, but were not able to maintain continuous populations. White pine pollen appeared at about 6200 yr B. P. accompanied by increased oak and alder pollen and decreased herbaceous pollen. If modern greenhouse gas-influenced climate becomes warm and dry, we deduce from the middle Holocene pollen results that the forest should become more open and eventaully prairie vegetation would expand into the area. If the climate becomes warm and wet, increased growth of oak on the upland and alder in low-lying wetter areas is expected. Expansion of alder will change the chemistry of lake waters by increasing nitrogen inputs stimulating growth of aquatic weeds and algae and resulting in increased sedimentation rates of lakes.
KEY WORDS: mid-holocene climate, landscape change, global warming