Paleolimnological records of climatic change in North America

Lacustrine fossil records provide long time series of data on limnological and climatic conditions; these data are useful for establishing natural patterns of climate variability and for generating testable hypotheses about atmospheric circulation and climate-ecosystem linkages. Shoreline features can indicate past lake-level fluctuations that may reflect changes in moisture balance, but often these records are discontinuous and are evidence of only extreme conditions. The organisms, geochemistry, and sedimentology of lake sediments may provide a more continuous sequence of direct and indirect lake-climate interactions in the past. The most clearly interpretable paleolirnnological records of climatic change are those that use several lines of evidence to corroborate a climatic hypothesis and are from sites near an ecotone or in regions of extreme climate. In all cases, hydrologic setting mediates a lake's response to climate and must be considered in interpreting sedimentary sequences. Discussion of the impact of recent and future climatic changes necessitates a baseline against which the mag-nitude of observed or predicted changes can be measured