Enhanced Dissolved Iron Promoted Microbial Blooms in the Aftermath of the End-Permian Mass Extinction

The ecological dominance of cyanobacteria following mass extinctions represents a pivotal yet enigmatic phase in Earth’s biotic recovery. While these blooms are well-documented, the driving mechanisms and the interplay between microbial biogeochemistry and environmental perturbations remain poorly constrained. This study presents high-resolution carbonate iron isotope (δ56Fe) data from a Permian-Triassic boundary section in South China to reveal the critical role of microbial iron cycling in controlling the dynamics of cyanobacterial proliferation. Our record reveals distinct negative δ56Fe excursions during the extinction horizon, clearly linking these shifts to microbial iron reduction. We propose that iron-reducing bacteria, fueled by enhanced terrestrial input, liberated substantial dissolved Fe(II) reservoirs, creating a positive feedback loop that catalyzed cyanobacterial expansion. Our findings establish carbonate δ56Fe as a promising proxy for microbial iron cycling during paleoenvironmental crises and provide a mechanistic framework for understanding microbial resilience and biogeochemical cycling during the most severe extinction event in Earth’s history.