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1. Subtropical sea-surface warming and increased salinity during Eocene Thermal Maximum 2

   https://doi.org/10.1130/G39658.1  

   Harper, Dustin T.; Zeebe, Richard; Hönisch, Bärbel; Schrader, Cindy D.; Lourens, Lucas J.; Zachos, James C. (December 2017, Geology)
2. Response of Coastal California Hydroclimate to the Paleocene-Eocene Thermal Maximum

   https://doi.org/10.5194/cp-2023-89  

   Zhang, Xiaodong; Tipple, Brett J; Zhu, Jiang; Rush, William D; Shields, Christian A; Novak, Joseph B; Zachos, James C (November 2023, European Geosciences Union)

   Abstract. The effects of anthropogenic warming on the hydroclimate of California are becoming more pronounced, with increased frequency of multi-year droughts and flooding. As a past analog for the future, the Paleocene-Eocene Thermal Maximum (PETM) is a unique natural experiment for assessing global and regional hydroclimate sensitivity to greenhouse gas warming. Globally, extensive evidence (i.e., observations, climate models with high pCO2) demonstrates hydrological intensification with significant variability from region to region (i.e., dryer or wetter, or greater frequency and/or intensity of extreme events). Central California (paleolatitude ~42° N), roughly at the boundary between dry subtropical highs and mid-latitude low pressure systems, would have been particularly susceptible to shifts in atmospheric circulation and precipitation patterns/intensity. Here, we present new observations and climate model output on regional/local hydroclimate responses in central California during PETM. Our findings based on multi-proxy evidence within the context of model output suggest a transition to an overall drier climate punctuated by increased precipitation during summer months along the central coastal California during the PETM. 

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3. Response of coastal California hydroclimate to the Paleocene–Eocene Thermal Maximum

   https://doi.org/10.5194/cp-20-1615-2024  

   Zhang, Xiaodong; Tipple, Brett J; Zhu, Jiang; Rush, William D; Shields, Christian A; Novak, Joseph B; Zachos, James C (January 2024, Climate of the Past)

   Abstract. The effects of anthropogenic warming on the hydroclimate of California are becoming more pronounced with the increased frequency of multi-year droughts and flooding. As a past analog for the future, the Paleocene–Eocene Thermal Maximum (PETM) is a unique natural experiment for assessing global and regional hydroclimate sensitivity to greenhouse gas warming. Globally, extensive evidence (i.e., observations and climate models with high pCO2) demonstrates hydrological intensification with significant variability from region to region (i.e., drier or wetter, greater frequency, and/or intensity of extreme events). Central California (paleolatitude ∼ 42° N), roughly at the boundary between dry subtropical highs and mid-latitude low-pressure systems, would have been particularly susceptible to shifts in atmospheric circulation and precipitation patterns/intensity. Here, we present new observations and climate model output on regional/local hydroclimate responses in central California during the PETM. Our findings, based on multi-proxy evidence within the context of model outputs, suggest a transition to an overall drier climate punctuated by increased precipitation during summer months along central coastal California during the PETM. 

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4. Millennial-timescale thermogenic CO2 release preceding the Paleocene-Eocene Thermal Maximum

   https://doi.org/10.1038/s41467-025-60939-3  

   Jiang, Shijun; Cui, Ying; Wang, Yasu; De_Palma, Maurizia; Naafs, B_David_A; Jiang, Jingxin; Hu, Xiumian; Wu, Huaichun; Chu, Runjian; Gu, Yangguang; et al (June 2025, Nature Communications)

   Abstract Geologic records support a short-lived carbon release, known as the pre-onset excursion (POE), shortly before the Paleocene-Eocene Thermal Maximum (PETM; ~ 56 Ma). However, the source and pace of the POE carbon release and its relationship to the PETM remain unresolved. Here we show a high-temporal-resolution stratigraphic record spanning the POE and PETM from the eastern Tethys Ocean that documents the evolution of surface ocean carbon cycle, redox and eutrophication, confirming the global nature of the POE. Biomarkers extracted from the sedimentary record indicate a smaller environmental perturbation during the POE than that during the PETM in the eastern Tethys Ocean. Earth system modeling constrained by observed δ¹³C and pH data indicates that the POE was driven by a largely thermogenic CO₂source, likely associated with sill intrusions prior to the main eruption phase of the North Atlantic Igneous Province and possibly biogeochemical feedbacks involving the release of biogenic methane. 

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5. Astrochronology of the Paleocene-Eocene thermal maximum on the Atlantic coastal plain

   Mingsong Li, Timothy J (September 2022, Nature communications)

   The chronology of the Paleocene-Eocene Thermal Maximum (PETM, ~56 Ma) remains disputed, hampering complete understanding of the possible trigger mechanisms of this event. Here we present an astrochronology for the PETM carbon isotope excursion from Howards Tract, Maryland a paleoshelf environment, on the mid-Atlantic Coastal Plain. Statistical evaluation of variations in calcium content and magnetic susceptibility indicates astronomical forcing was involved and the PETM onset lasted about 6 kyr. The astrochronology and Earth system modeling suggest that the PETM onset occurred at an extreme in precession during a maximum in eccentricity, thus favoring high temperatures, indicating that astronomical forcing could have played a role in triggering the event. Ca content data on the paleo-shelf, along with other marine records, support the notion that a carbonate saturation overshoot followed 

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