Jacob J., Huang Y. S., Disnar J. R., Sifeddine Abdelfettah, Boussafir M., Albuquerque A. L. S., Turcq Bruno. (2007). Paleohydrological changes during the last deglaciation in Northern Brazil. Quaternary Science Reviews, 26 (7-8), p. 1004-1015. ISSN 0277-3791.
Titre du document
Paleohydrological changes during the last deglaciation in Northern Brazil
Jacob J., Huang Y. S., Disnar J. R., Sifeddine Abdelfettah, Boussafir M., Albuquerque A. L. S., Turcq Bruno
Source
Quaternary Science Reviews, 2007,
26 (7-8), p. 1004-1015 ISSN 0277-3791
We here report a reconstruction of hydrological balance variations in Northern Brazil for the last 20 ka deduced from the delta D values of aquatic and land plant molecules extracted from the sediment infill of Lake Caco. Our reconstructed precipitation, lake water isotope ratio and evaporation-evapotranspiration isotope effect allows us to obtain an estimate of moisture balance, and, to a lesser extent, precipitation amount and seasonality changes. During the end of the Last Glacial Maximum (LGM, between ca 20 and 17.3 ka), high delta D values and smaller fractionation of leaf waxes indicate an and to semi-arid climate with a long lasting dry season. An abrupt change towards much wetter conditions occurred within ca 500 years from 17.3 to 16.8 ka, as shown by a 50 parts per thousand decrease in D/H ratios and a marked increase in H isotopic fractionation of leaf waxes. This abrupt isotopic change coincides with a major transformation from savanna-dominated vegetation to humid rain forest around the lake, based on pollen data. Comparisons with other paleo-precipitation records from South American sites indicate that Lateglacial humid conditions were controlled by intensification of the ITCZ and/or a southward shift of its mean position across our study site. Our isotope data show only a small rise in aridity during Younger Dryas event (13-11.5 ka). Although the Holocene was not screened in details, D/H ratios of terrestrial and aquatic compounds show near constant offsets, suggesting stable and relatively humid climate conditions during this period.
