Diatom-based transfer functions for salinity, precipitation and temperature were developed using a training set that included data from 40 sites along central Mexico. These transfer functions showed good performance parameters and were subsequently applied to the previously published diatom record from lake Chalco, southern Basin of Mexico. Heinrich stadials (HS-3 to HS-0) were reconstructed as cold and dry events, with HS-2 representing the coldest and driest conditions, while HS-1 shows a complex bimodal cooling pattern. Orbital scale variability is also recorded. High and variable lake salinities from ∼34 to 29 ka BP (marine isotope stage 3, MIS-3) corresponded with times of maximum summer insolation and evidences of frequent fires. MIS-2 was identified as a cold period, with low lake salinity associated with low evaporation, with two cold intervals during the minima in spring (∼25.5 ka BP) and summer (∼20 ka BP) insolation. The ∼20 ka BP cold event together with HS-2 (24-23 ka BP), defined a bimodal maximum cooling during the last glacial maximum (LGM: 24.5–19.5 ka BP) within the range of pollen-based estimates, further supporting a maximum tropical cooling of 4–5 °C for the LGM. The deglacial (19.5–11.5 ka BP) showed the highest precipitation anomalies with three peaks that closely correlated with glacier advances in the nearby mountains (Iztaccihuatl). The early Holocene marked a change towards high lake salinities and the highest positive temperature anomalies (+3.5 °C) during a peak in summer insolation. Even though at orbital scale Chalco showed a nearly opposite trend to the record from the more southerly lake Peten-Itza (Guatemala), at millennial scale it showed a common pattern of cold and dry conditions during HSs, comparable to other tropical latitude sites in the northern hemisphere and further supporting the idea that there is a strong coupling between tropical and higher latitudes climates, in particular with the North Atlantic.
Bibliographical noteFunding Information:
The authors would like to thank Dr. Ma. Aurora Armienta and the staff in the Analytical Chemistry Laboratory at the Institute of Geophysics, National University of Mexico, for major ions analysis of the BM and the TMVB lakes and to Dra. Gabriela Vázquez and Ariadna Martínez, Instituto de Ecología AC, for major ions analysis of the “Los Tuxtlas” samples. We also thank Dr. Susana Sosa, Dr. Ana María Soler and Dr. Cecilia Caballero for technical support during field and laboratory work. This research was supported by grants DGAPA-PAPIIT - IV100215 , CONACyT C0005-190519 and CONACyT 167621 .
© 2018 Elsevier Ltd
Copyright 2019 Elsevier B.V., All rights reserved.
- Late Pleistocene
- North America
- Transfer functions
Continental Scientific Drilling Facility tags