Ocean circulation changes rather than global warming drove temperature trends across the Miocene Climatic Optimum.

Authors

Evi Wubben, Xiaoqing Liu, Tjerk J T Veenstra, R Paul Acosta, Joyce den Hollander, Chris Overduin, Matthew Huber, Francesca Sangiorgi, Francien Peterse, Appy Sluijs

Published in

Science advances. Volume 12. Issue 41. Pages eadz2555. Oct 09, 2026. Epub Oct 09, 2026.

Abstract

Early-to-Middle Miocene [23 to 13.8 million years ago (Ma)] climates were ∼6° to 9°C warmer than today. Around 16.9 Ma, benthic foraminiferal oxygen isotope (δ¹⁸O) records suggest pronounced warming, known as the Miocene Climatic Optimum (MCO) onset. However, explaining this putative global warming with carbon dioxide (CO₂) forcing faces challenges in terms of timing and forcing magnitude. Our new biomarker-based ocean temperature records, combined with published data, reveal no substantial mean global upper ocean warming across the MCO. Instead, temperature changes differ considerably between sites, with some regions showing cooling. Climate model sensitivity tests indicate that these patterns are best explained by ocean circulation changes, likely due to gateway changes and Antarctic ice sheet variations. This suggests that the MCO signature is better attributed to ocean circulation changes rather than a CO₂-driven global warming event. The δ¹⁸O signal therefore represents warmer deepwater sourcing and/or reduced Antarctic glacial volume, resolving the longstanding challenge of explaining MCO warming without a pronounced CO₂ rise.

PMID:
42853949
Bibliographic data and abstract were imported from PubMed on 10 Oct 2026.

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