Pollen and non-pollen palynomorphs of Lake Chalco as indicators of paleolimnological changes in high-elevation tropical central Mexico since MIS 5

Aquatic pollen and non-pollen palynomorphs (NPPs) from a 72-m-long sediment core from Lake Chalco in central Mexico document macrophyte vegetation and paleolimnological conditions during the last glacial (∼85–10.8 k cal a BP). We compared macrophyte vegetation and NPP records with data for authigenic carbonate deposition estimated from concentrations of total inorganic carbon. We estimated saline and variable trophic conditions during the last glacial. An association indicative of higher salinity conditions characterized by NPP and diatom assemblages characteristic of alkaline and saline environments is documented. Changes in hydrophyte taxa and microalgae assemblages were related to trophic level fluctuations. Higher salinity environments were contemporary with arid intervals reconstructed based on abundances of inorganic carbonate. Two main periods were evident in this record: (i) 85–29 k cal a BP [Marine Isotope Stage (MIS) 5b–MIS 3] characterized by saline conditions with high abundance of Type-TXA, and variable high carbonate content, and (ii) 29–10.8 k cal a BP (MIS 2–MIS 1) when conditions changed to higher trophic levels and lower salinities, characterized by extremely low values of Type-TXA and carbonate content. Spring and summer insolation and latitudinal position of the Intertropical Convergence Zone over the last glacial were considered as possible controllers of the recorded paleoenvironmental changes.