The drivers of the Middle Eocene Climatic Optimum (MECO) remain enigmatic. Here we report a high-resolution terrestrial MECO record from the Bohai Bay Basin, eastern China. The record shows episodic Hg enrichments and a volcanogenic Δ¹⁹⁹Hg signature during the MECO, and an abrupt chemical weathering enhancement and negative δ¹³C_org excursion (CIE) during the MECO peak warmth. A high-resolution age model constrains the MECO to ca. 40.59–40.18 Ma with the onset in the first ~320 k.y. Peak warmth and the CIE initiated at 40.27 Ma, corresponding to 405 k.y. and 100 k.y. eccentricity maxima, and lasted for ~90 k.y., reminiscent of the early Eocene hyperthermals. Our findings suggest that episodic volcanism contributed to gradual atmospheric pCO₂ rise, leading to the long duration of the MECO onset. Orbital forcing at 40.27 Ma, on top of CO₂ forcing, caused the peak warmth and a positive carbon cycle feedback. The regional increase in weathering is inconsistent with evidence for weakened global continental weathering, suggesting strong spatial heterogeneity in the weathering response to MECO warming.