Flavio Anselmetti, Swiss Federal Institute of Aquatic Science & Technology (Eawag) (Switzerland)
David Hodell, University of Florida (United States)
Daniel Ariztegui, University of Geneva (Switzerland)
Mark Brenner, University of Florida (United States)
Jason Curtis, University of Florida (United States)
Jaime Escobar, University of Florida (United States)
Adrian Gilli, ETH Zürich (Switzerland)
Dustin Grzesik, University of Florida (United States)
Steffen Kutterolf, IFM-GEOMAR (Germany)
Andreas Mueller, ETH Zürich (Switzerland)
As part of an ICDP drilling campaign, 1327 m of lake sediment were recovered in early 2006 at seven sites in Lake Petén Itzá, a closed basin lake in northern Guatemala. The completely recovered sediments provide a record of terrestrial climate change from lowland Central America extending back to 200 ka. Research has focused thus far on Site PI-6 at a water depth of 71 m where three holes were drilled to a maximum depth of 75.9 mblf (85 ka).
Due the lake's closed hydrology, water level fluctuates strongly controlled by past evaporation/precipitation patterns. As a consequence, Lake Petén Itzá's sediments respond accordingly and vary between gypsum-rich lithologies (lowstand) and clay-rich units (highstands). Interpreting this climate-sensitive sedimentologic succession, we found that Petén climate varied between wetter conditions during interstadials and a drier state during stadials of Marine Isotope Stage (MIS) 3. The most arid periods coincided with Heinrich Events in the North Atlantic and reductions in the strength of meridional overturning circulation. The pattern of clay-gypsum (wet-dry) oscillations during MIS 3 closely resembles the temperature record from Greenland ice cores and North Atlantic marine sediment cores and precipitation proxies from the Cariaco Basin.
Contrary to previous findings, the Last Glacial Maximum (LGM) from ∼23 to 18 ka was moist in the Petén lowlands and vegetation consisted of a temperate pine-oak forest. Greater moisture availability was likely related to increased winter precipitation associated with frequent polar outbreaks (i.e., cold fronts) or "Nortes" (northerly winds), which occasionally bring rain to northern Guatemala today during the dry season. At the end of the LGM, Petén climate switched from moist to arid conditions from 18 to 14.7 ka. Moister conditions prevailed during the warmer Bolling-Allerod (14.7 to 12.8 ka), with the exception of a brief return to dry conditions at 13.8 ka. The onset of the Younger Dryas at 12.8 ka marked the return of dry conditions. Pollen assemblages indicate that a mesic forest had been largely established by 11.3 ka, but sediment properties suggest that the lake continued to precipitate gypsum until 10.35 ka. Our results support the hypothesis that summer precipitation was controlled by migrations in the meridional position of the Atlantic ITCZ during the MIS 3 and the last deglaciation. The ITCZ was located farther south during cold periods, especially during Heinrich Events, and arid conditions prevailed in the northern hemisphere Neotropics.
The deepest section of hole PI-7, reaching a maximum subsurface depth of 133 m, recovered below an unconformity an older sedimentary section that, according to a first tephrachronlogy, dates back to ∼200 ka, providing a so far unmatched archive of terrestrial climate change in the Central Americas.