Description: Long sediment cores were collected in spring 2006 from Lake Petén Itzá, northern Guatemala, in water depths ranging from 30 to 150 m, as part of an International Continental Scientific Drilling Program project. The sediment records from deep water consist mainly of alternating clay, gypsum and carbonate units and, in at least two drill sites, extend back 〉200 kyr. Most of the lithostratigraphic units are traceable throughout the basin along seismic reflections that serve as seismic stratigraphic boundaries and suggest that the lithostratigraphy can be used to infer regional palaeoenvironmental changes. A revised seismic stratigraphy was established on the basis of integrated lithological and seismic reflection data from the basin. From ca 200 to ca 85 ka, sediments are dominated by carbonate-clay silt, often interbedded with sandy turbidites, indicating a sediment regime dominated by detrital sedimentation in a relatively humid climate. At ca 85 ka, an exposure horizon consisting of gravels, coarse sand and terrestrial gastropods marks a lake lowstand or partial basin desiccation, indicating dry climate conditions. From ca 85 to ca 48 ka, transgressive carbonate-clay sediments, overlain by deep-water clays, suggest a lake level rise and subsequent stabilization at high stage. From ca 48 ka to present, the lithology is characterized by alternating clay and gypsum units. Gypsum deposition correlates with Heinrich Events (i.e. dry climate), whereas clay units coincide with more humid interstadials.

Description: Drill cores obtained from Lake Petén Itzá, Petén, Guatemala, contain a ∼85-kyr record of terrestrial climate from lowland Central America that was used to reconstruct hydrologic changes in the northern Neotropics during the last glaciation. Sediments are composed of alternating clay and gypsum reflecting relatively wet and dry climate conditions, respectively. From ∼85 to 48 ka, sediments were dominated by carbonate clay indicating moist conditions during Marine Isotope Stages (MIS) 5a, 4, and early 3. The first gypsum layer was deposited at ∼48 ka, signifying a shift toward drier hydrologic conditions and the onset of wet–dry oscillations. During the latter part of MIS 3, Petén climate varied between wetter conditions during interstadials and drier states during stadials. The pattern of clay–gypsum (wet–dry) oscillations during the latter part of MIS 3 (∼48–23 ka) closely resembles the temperature records from Greenland ice cores and North Atlantic marine sediment cores and precipitation proxies from the Cariaco Basin. The most arid periods coincided with Heinrich Events when cold sea surface temperatures prevailed in the North Atlantic, meridional overturning circulation was reduced, and the Intertropical Convergence Zone (ITCZ) was displaced southward. A thick clay unit was deposited from 23 to 18 ka suggesting deposition in a deep lake, and pollen accumulated during the same period indicates vegetation consisted of a temperate pine-oak forest. This finding contradicts previous inferences that climate was arid during the Last Glacial Maximum (LGM) chronozone (21±2 ka). At ∼18 ka, Petén climate switched from moist to arid conditions and remained dry from 18 to 14.7 ka during the early deglaciation. Moister conditions prevailed during the warmer Bolling–Allerod (14.7–12.8 ka) with the exception of a brief return to dry conditions at ∼13.8 ka that coincides with the Older Dryas and meltwater pulse 1A. The onset of the Younger Dryas at 12.8 ka marked the return of gypsum and hence dry conditions. The lake continued to precipitate gypsum until ∼10.3 ka when rainfall increased markedly in the early Holocene.