Environmental and Hydrological Changes of Lake Coatetelco in Central Mesoamerica (Southwest Mexico) Over the Holocene and Comparison With Climatic Forcing

Elemental composition of the inorganic fraction, carbon isotopes, and C/N of organic matter from a new radiocarbon-dated sedimentary sequence collected from Lake Coatetelco (960 m asl) extend information about the environmental and hydrological conditions of central Mesoamerica from the earliest Holocene to the interval of first human settlements in the lake vicinity and nearby streams. Proxy-based reconstructions of erosion/runoff (Ti), water column salinity (CaCO3), sediment-water interactions (PIA), and provenance of organics (delta C-13(org) and C/N) showed similarities with the summer insolation modulated ITCZ position between similar to 11.5 and 4.2 cal ka BP, and more frequent ENSO between similar to 4.2 and 2.1 cal ka BP. After a possible depositional hiatus between similar to 11.2 and 10.2 cal ka BP, the moderate-to-extremely altered sediments were deposited with enhanced erosion/runoff during the wetter similar to 10.2-6 cal ka BP and the organic matter was dominantly autochthonous. Comparison of delta C-13(org) and C/N suggested that the contribution of C-4 plants to organic matter increased over the drier similar to 6-4.2 cal ka BP. Sediments representing this middle- Holocene drought-like condition showed geochemical similarity with sediments of the Post-Classic drought (similar to 1-0.4 cal ka BP), coeval with abandonment of the Xochicalco culture. Variation in seasonal insolation at orbital scales might have forced frequent droughts between similar to 6 and 4.2 cal ka BP and the ENSO related short-lived storms possibly led to an unstable hydroclimate after similar to 4.2 cal ka BP when the first Olmec settlements commenced in the region. Dissimilarity between this lacustrine archive and speleothems from southwest Mexico for the later part of the Holocene reflected different sensitivities of the geological records to seasonal and-annual precipitation.