Ocean Acidification

Highlights

• Multi-proxy reveals a sequence of ocean acidification, warming and anoxia across the PETM.
• We document pre-onset biotic stress, causing ecosystem to deteriorate before the PETM.
• Synergistic ocean warming, anoxia and acidification drove ecological reorganization.
• The study provides a geo-analogue for projecting future trajectory of ocean ecosystem.

Abstract

The Paleocene–Eocene Thermal Maximum (PETM) represents a pivotal geological analog for modern anthropogenic climate change, yet the precise temporal sequence of environmental stressors that drove severe biotic crisis remains elusive. Here, we present an integrated, multi-proxy record, including bulk carbonate and foraminiferal stable isotopes (δ¹³C, δ¹⁸O), and elemental ratios (Mg/Ca, B/Ca, U/Ca) from a Tethyan marine sequence (Tarfa section, Egypt), that captures the full PETM progression. Our data document four distinct phases of environmental and biotic changes. First, the pre-onset phase shows that initial foraminiferal decline is closely linked to precursor shifts in δ¹³C, δ¹⁸O, and early deoxygenation. This demonstrates that marine ecosystem stress began before the PETM carbon isotope excursion (CIE). Second, the PETM onset featured a severe carbonate dissolution (<1 wt%), forming a regional clay bed that caused benthic extinction and planktic decline. Third, the main body phase is characterized by a pronounced CIE (∼3.7‰), extreme warming (Mg/Ca-derived temperature increase of ∼5 °C, peaking at ∼35 °C), and pervasive deoxygenation (elevated U/Ca), which acted synergistically to drive ecological turnover and dwarfing. Lastly, the recovery phase is marked by a carbonate overshoot, gradual geochemical stabilization, and biotic rebound. Together, these findings reveal a phased cascade of stressors—initial carbon cycle instability, ocean acidification, and prolonged warming and deoxygenation—that reshaped marine ecosystems sequentially. This study therefore provides a template for understanding multi-stressor interactions and biotic resilience during rapid hyperthermal events, which has critical implications for predicting the future scenario of anthropogenic forcing.

Salman A. M., Chen Z., Wang X., Cui L., Li H. & Wang X., 2026. Multi-stressor-driven biotic upheaval across the PETM: a perspective from elemental and isotope ratios of foraminiferal and bulk carbonate in the southern Tethyan shelf. Global and Planetary Change 267: 105751. doi: 10.1016/j.gloplacha.2026.105751. Article (subscription required).