137 Joint SGD-SEPM-IAS Focus on the Sedimentary Record of Climate Change

Explore how sedimentary records reveal Earth's climatic history and processes driving environmental change. This session highlights proxies, stratigraphy, and emerging technologies, advancing understanding of past climates and informing predictions of future climate dynamics through interdisciplinary collaboration.

Monday, 20 October 2025
1:30 PM - 5:30 PM
HBGCC, 303C

Reconstructing Hydroclimate Variability in the Basin of Mexico Over the Past 400 ka Using Triple Oxygen Isotopes in Lake Chalco Carbonates

Paper number: 137-6
Program: Technical Sessions
Time: 2:55 PM – 3:10 PM

Authors

Abstract

Tropical paleoclimate records extending beyond the Last Glacial Maximum remain limited, constraining our ability to resolve long-term hydroclimate variability in low-latitude regions. To address this gap, we reconstruct the evaporation history of Lake Chalco in the Basin of Mexico using triple oxygen isotope (δ′18O, Δ′17O) measurements from authigenic carbonates preserved in a continuous sediment core spanning ~400 ka and ~300 meters in depth (Hodgetts et al., 2025).

Measured carbonate Δ′17O values range from –15 to –195 per meg (VSMOW), while δ′18O values range from ~24 to 33‰ (VSMOW). Despite modern precipitation in the region having δ′18O values as low as –7 to –10‰ (VSMOW), carbonate δ′18O values remain unexpectedly high (2–3‰ VPDB or ~33–34‰ VSMOW), indicating strong and persistent evaporative enrichment. These enrichments persist across multiple glacial–interglacial cycles (MIS 11 to MIS 2), underscoring the lake’s sensitivity to evaporation-driven isotope effects through time.

Using a Craig-Gordon–based lake evaporation model, we assessed the influence of initial meteoric water δ′18O, relative humidity, and the fraction of lake evaporation on the observed isotopic signals. We find that Δ′17O carbonate values for all glacial-interglacial MIS stages except MIS 7 are consistent with steady-state evaporation, assuming θdiff of 0.511 for diffusive fractionation (Angert et al., 2004), under moderate relative humidity (30-55%) and evaporation fractions of ~40-80%. The reconstructed meteoric water δ′18O values (–17‰ to –5.7‰) and Δ′17O values (20-35 per meg) help constrain past precipitation sources and atmospheric circulation patterns. 

MIS 7 interglacial stage stands out as a notable exception, with moderate δ′18O ~24 to 28‰ (VSMOW) and more positive Δ′17O values ranging from -56 to -100 per meg, indicate reduced evaporation and a greater contribution from summer precipitation. This suggests wetter conditions and potentially intensified monsoonal input during this period.

These findings demonstrate the utility of triple oxygen isotope measurements for disentangling evaporation dynamics in closed-basin lakes and provide new insights into tropical hydroclimate evolution in central Mexico over the past 400 ka.

Geological Society of America Abstracts with Programs. Vol. 57, No. 6

doi: 10.1130/abs/2025AM-413953

© Copyright 2025 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes. Permission is hereby granted to any individual scientist to download a single copy of this electronic file and reproduce up to 20 paper copies for noncommercial purposes advancing science and education, including classroom use, providing all reproductions include the complete content shown here, including the author information. All other forms of reproduction and/or transmittal are prohibited without written permission from GSA Copyright Permissions.