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 degrees 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.

Automated summary

The study found that the Basin of Mexico responded differently to orbital changes from late MIS 6 to MIS 3, including lake productivity, vegetation, and fire events. The paleoenvironmental reconstruction showed that in the past, wetter periods were often accompanied by dry conditions, low forest cover, and low fire activity; while under high spring insolation, the environment suddenly shifted from wet to dry, leading to increased forest cover and fire activity.