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Lago de Patzcuaro lies at an elevation of 2035 m (19 degrees 36’ N 101 degrees 39’ W) on the west part of the volcanic Meseta Central of Mexico, about 50 km east-southeast of Morelia. Pollen, diatom, acid geochemical records from a 15 m core taken in 6 m of water continuously track vegetation and limnological changes in the Patzcuaro basin for the past 38 ky (calendar years). Pine, oak, and alder pollen dominate both the Wisconsin and Holocene vegetation record, and indicate that this region did not witness strongly arid climates during that time. Before the Holocene, Juniperus-type and Artemisia pollen document cooler climates of more effective moisture at least seasonally. Isoetes characterizes the full and late glacial interval (25-13 ka) and implies, along with the diatoms Aulacoseira and Stephanodiscus, cool, deep, freshwater conditions at Lago de Patzcuaro. The freshest and deepest lacustrine phase in the lake occurred 38 to 25 ka. During this time, Lago dr Patzcuaro may have drained into the Lerma River system. Between 30 and 10 ka, diatom species that bloom in the winter and early spring imply moisture during those seasons. Evaluation of contemporaneous marine acid terrestrial records west and east of Lago de Patzcuaro suggests that this moisture probably originated from westerly storm tracks shifted south by the Laurentide ice sheet. After 10 ka, Lago de Patzcuaro became shallower and more eutrophic. Rooted aquatic plants prospered under a climate regime of negative hydrologic budgets, increased seasonality, and moisture arriving during the summer as it does today. The lake became alkaline enough by the mid-Holocene to deposit ostracode-rich marls at the core site for the first time in the past 48 ky. Indigenous agriculture in the Patzcuaro drainage and around the lake appears about 4 ka, with the appearance of Zea and Chenopodiineae pollen. Iron and potassium track increased soil erosion, and planktic diatoms (Cyclostephanos) record nutrients flushed into the lake from the drainage basin. (C) 2000 Elsevier Science B.V. All rights reserved.