147 Climate, Ocean and Environmental Changes Through Earth History: From Marine and Terrestrial Proxies to Model Assessments (Posters)

This session brings together marine and terrestrial proxies and modelling to reconstruct rapid ocean, environment, and climate events, and shifts between long-term climate/ocean/environment states, within the context of normal variability throughout Earth history.

Monday, 20 October 2025
8:00 AM - 5:30 PM
HBGCC, Hall 1

Late Eocene-Oligocene Paleohydrology and Temperature Reconstructions from South China Sea

Paper number: 147-6
Program: Technical Sessions
Time: 8:30 AM – 8:45 AM

Authors

Abstract

The evolution of the East Asian Summer Monsoon (EASM) during the late Eocene–Oligocene transition (EOT) remains debated due to limited proxy records and contrasting regional interpretations. To address this gap, we generated high-resolution compound-specific carbon (δ¹³C) and hydrogen (δ²H) isotope records of leaf-wax n-alkanes from sediments of IODP Site U1501 in the northern South China Sea, spanning 35–20 Ma. These data, combined with sea-surface temperature (SST) estimates from TEX₈₆ and mean annual air temperature (MAAT) reconstructions from branched GDGTs, provide an integrated reconstruction of precipitation, temperature, and vegetation dynamics across this critical climatic interval.

Results reveal a significant enrichment of ~2.0‰ in δ¹³Cwax values across the EOT, suggesting reduced precipitation and increased plant water-use efficiency under drier conditions. TEX₈₆-derived SSTs show a ~5°C decline between 34.4 and 33 Ma, synchronous with global evidence for Antarctic glaciation. MAAT reconstructions indicate a ~4°C decrease in continental temperature, consistent with major climate reorganization during the EOT. The observed shifts in Paq index and n-alkane distribution further suggest changes in terrestrial versus aquatic vegetation inputs, likely linked to regional hydrological stress.

These findings demonstrate that the South China region experienced humid, monsoon-dominated conditions in the late Eocene, followed by marked aridification during the early Oligocene, concurrent with global ice growth. This integrated multi-proxy record provides the first direct isotopic evidence from the South China Sea of EASM weakening across the EOT and highlights the strong coupling between global climate forcing and Asian hydroclimate evolution.

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

doi: 10.1130/abs/2025AM-414740

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