Abrupt Younger Dryas cooling in the northern tropics recorded in lake sediments from the Venezuelan Andes

摘要

A radiocarbon dated sediment record from Laguna de Los Anteojos, a cirque lake in the Merida Andes of Venezuela, indicates that warmer and wetter atmospheric conditions occurred in the northern tropics at the onset of the Belling (similar to 14,600 cal yr BP), and abruptly colder and drier conditions around the time of the Younger Dryas (YD). Geochemical and clastic sediment analyses from Los Anteojos show that glaciers advanced at similar to 12,850 cal yr BP, reached their YD maximum extent at similar to 12,650 cal yr BP, and then retreated until complete deglaciation of the watershed at similar to 11,750 cal yr BP. The onset of warmer conditions that ended the coldest phase of the YD occurred several hundred years earlier at Los Anteojos than in the high latitudes of the Northern Hemisphere. During the peak YD glacial advance, glacier equilibrium-line altitudes in the region were similar to 360 to 480 m lower, and temperature was similar to 2.2 to 2.9 degrees C colder than modern. Independent palynological evidence from the Los Anteojos sediment core indicates that the northern Andes were more arid and at least 2.3 degrees C colder during the YD. The direction and timing of glacial fluctuations in Venezuela are consistent with observations of marine sediment records from the Cariaco Basin that suggest abrupt cooling occurred at similar to 12,850 cal yr BP, followed by a shift to higher temperature after similar to 12,300 cal yr BP. The timing and pattern of climatic changes in northern South America are also consistent with paleoclimate records from the southern Tropical Andes that suggest a southward shift in the position of the Intertropical Convergence Zone occurred at the start of the cooling event, followed by a return to wetter conditions in northern South America during the late stages of the YD. The early warming of the tropical atmosphere and invigoration of the hydrologic cycle likely contributed to the shift to increased temperature in the higher latitudes of the Northern Hemisphere at the end of the late Glacial stage.