HR: 08:30h
AN: PP21D-03    [Abstracts]
TI: Holocene climatic change in the northern Midwest: a comparison of updated paleoclimate reconstructions and new regional climate model experiments.
AU: * Shuman, B
EM: bshuman@umn.edu
AF: University of Minnesota, Department of Geography 414 Social Science Building, Minneapolis, MN 55455 United States
AU: Williams, J W
EM: jww@geography.wisc.edu
AF: University of Wisconsin, Department of Geography 550 North Park St., Madison, WI 53706 United States
AU: Diffenbaugh, N S
EM: diffenbaugh@purdue.edu
AF: Purdue University, Department of Earth and Atmospheric Sciences 550 Stadium Mall Drive, West Lafayette, IN 47907-2051 United States
AU: Bartlein, P J
EM: bartlein@uoregon.edu
AF: University of Oregon, Department of Geography, Eugene, OR 97403 United States
AB: The mid-continent of North America has long been recognized to have experienced a period of pronounced aridity during the mid-Holocene. A mechanistic explanation for these drier-than-modern conditions, however, has been elusive. Past GCM simulations of 6000 yrs B.P. have failed to produce the strong moisture anomalies inferred from pollen, lake level, diatom, and isotope data, perhaps because important ocean- and land-surface feedbacks were not incorporated into model experiments and because of the coarse resolution of GCMs. Here, we present an updated synthesis of paleoclimatic data from the upper Midwest for comparison with new regional climate model simulations of 6000 yrs B.P. using RegCM2. We focus our analysis on changes in the seasonality of precipitation that may inform our understanding of the climate processes underlying the arid conditions. We use the modern analog technique to infer seasonal moisture levels from fossil pollen data and a simple hydrologic box model to evaluate the seasonal inputs to past lake levels. Patterns in pollen, lake-level, and isotope data support the idea that the dry conditions arose from lower than modern winter precipitation at 6000 yrs B.P.; but existing hypotheses about the dry conditions have often emphasized the contribution of greater than modern summer insolation for producing either high summer evaporative losses or severely reduced summer precipitation as also occurred during the 1930s Dust Bowl drought. Our new RegCM2 simulations appear consistent with our data synthesis. They show widespread negative moisture-balance anomalies in winter and spring, as well as large positive moisture-balance anomalies in summer. The consistency between the data and model imply a need to develop a new framework for understanding the mid-Holocene in the upper Midwest.
DE: 0429 Climate dynamics (1620)
DE: 0473 Paleoclimatology and paleoceanography (3344, 4900)
DE: 1626 Global climate models (3337, 4928)
DE: 1637 Regional climate change
DE: 1812 Drought
SC: Paleoceanography and Paleoclimatology [PP]
MN: Fall Meeting 2005