The Permian-Triassic hyperthermal event is characterized by extreme temperature rises and global carbon cycle perturbations. However, the ultimate drivers of the temperature rise remain poorly understood, leaving a key question surrounding the trigger for the Permian-Triassic mass extinction. Here, we evaluate the volcanic carbon emissions and carbon sequestration from the oceanic biological carbon pump (BCP) using Earth system model and proxy data. We infer a transition from a CO₂ source with a thermogenic carbon isotopic signature associated with a slower emission rate to a heavier, more mantle-dominated volcanic source with an increased rate of emissions. This implies that the CO₂ degassing style changed as the Siberian Traps emplacement evolved, consistent with geochemical proxy records. Meanwhile, carbon cycle positive feedbacks from ocean BCP may have further amplified the warming. We observe a three-fold increase in the vertical carbon isotope (δ¹³C) gradient between dissolved inorganic carbon (DIC) of the surface water and mid-water during the Permian-Triassic hyperthermal events. Earth system modeling suggests that higher rates of organic matter remineralization, driven by increased microbial respiration during warming intervals, are the main trigger for increased vertical δ¹³C_DIC gradients. Our results show that warming-induced increases in microbial metabolism cause a remarkable six-fold drop in POC transfer efficiency, leading to reduced organic carbon sequestration within the ocean interior. This implies that warming-induced increases in microbial metabolism act as positive feedback, exacerbating the Permian-Triassic hyperthermal event.

global warming, end-Permian, Earth system modeling, carbon cycling