A LAST GLACIAL MILLENNIAL SCALE RECORD FROM LAKE CHALCO, BASIN OF MEXICO

The last Glacial interval was characterized by millennial-scale climate oscillations named Dansgaard-Oeschger (D/O) events consisting of an abrupt warming followed by a gradual cooling. These events, first documented in the Greenland ice cores, have also been found in tropical locations. The basin of Mexico (20ºN, 99ºW; 2240 m.a.s.l.) is a tropical, high altitude, closed basin. It is surrounded by mountains up to 5400 m located at the northern limit of the American tropics. Lake Chalco is situated in the southern sub-basin with an area of 120 km². Previous studies in Lake Chalco have shown a continuous sedimentary record that provides information about Quaternary climate variability. A series of five cores were drilled reaching up to 122.5 m depth. The age of the upper part of the core has been established with several AMS 14C dates and by the presence previously dated tephra layers. Preliminary paleomagnetic analyses in the sequence indicate the presence of the Blake event (120,000 years) at ~72 m depth. Here we discuss the D/O events based on geochemical data, including total organic carbon (TOC), total inorganic carbon (TIC) and concentration of charcoal particles in the sedimentary register of Lake Chalco. A temporal correlation with D/O events reported for the Greenland icecap (GIPS2) is also presented. This preliminary data suggest that the slowing down of the thermohaline circulation affected the climate of central Mexico.