Climatic variability in the northern sector of the American tropics since the latest MIS 3.

We inferred millennial-scale climate variations and paleohydrological conditions in the northern sector of the American tropics for 30.3–5.5 cal ka BP using geochemical characteristics of sediments from Lake Chalco in central Mexico. The sediment sequence is chronologically constrained with three tephra and nine radiocarbon dates. Temporal variations in titanium, total inorganic carbon, total organic carbon/titanium ratio, carbon/nitrogen ratio, and silica/titanium ratio indicate changes in runoff, salinity, productivity, and sources. Higher concentrations of Ti indicate more runoff during latest Marine Isotope Stage (MIS) 3 (30.3–28.6 cal ka BP). Runoff was lower during the last glacial maximum (LGM; 23–19 cal ka BP) than during the Heinrich 2 event (26–24 cal ka BP). The interval of reduced runoff continued up to 17.5 cal ka BP but increased during the Bølling/Allerød. Trends of decreasing runoff and increasing salinity are observed throughout MIS 1. Lake Chalco received less runoff during the LGM compared to deglaciation, opposite the trend of other North American tropical records. Different amounts of rainfall at different sites are possibly due to shifts in the position of the Intertropical Convergence Zone, changes in the size of the Altlantic warm pool, and varying sea-surface temperatures of the Atlantic and Pacific oceans. [ABSTRACT FROM AUTHOR]