Environmental changes during MIS6-3 in the Basin of Mexico: A record of fire, lake productivity history and vegetation

The responses of lake productivity, vegetation, and fire events in the Basin of Mexico to orbital changes from late MIS 6 to MIS 3 (146–35 ka) have been studied based on geochemical (Ti, TIC, TOC, C/N), charcoal (CHAR) and pollen data of the sediment core CHA08 from Lake Chalco. The paleoenvironmental reconstruction identifies the MIS 6 as a wetter period with episodes of dry conditions, low forest cover and low fire activity. A sudden change from wetter to dry environments with low to high forest cover and fire activity episodes characterized the end of the MIS 6 (132–130 ka) coincident with high spring insolation. Variations in vegetation composition, with a tendency towards higher forest cover, fire-activity, runoff, and organic matter availability, are recorded during the MIS 5, MIS 4, and MIS 3. However, a reduction in the fire-activity was recorded for the cold and dry MIS 4. Spectral analysis based on the titanium concentration record of Lake Chalco suggests a precessional forcing on runoff variations. We explored the impact of the Intertropical Convergence Zone latitudinal migrations which have been related to the summer insolation at 65° N by comparing runoff data with other sedimentary records from North and Central America. Our results highlight the sensitivity of the high altitude tropical basin to climate variations.