Dynamic redox-promoted iron and nutrient cycling drove graptolite evolution across the Ordovician-Silurian transition.

ABSTRACT: Graptolites were abundant and cosmopolitan zooplankton in Early Paleozoic oceans, but a prominent change in species occurred across the Late Ordovician mass extinction. We use ocean redox, iron isotope (δ⁵⁶Fe), and phosphorus phase partitioning records from shelf and deep-ocean settings to evaluate the drivers behind this major reshaping of the pelagic marine ecosystem. A marked decrease in mesopelagic graptolites coincided with a stepwise negative δ⁵⁶Fe shift on the shelf, driven by partial seawater Fe drawdown resulting from episodic intensification of mid-depth euxinia. Subsequently, a positive δ⁵⁶Fe shift in both deep-ocean and shelf sediments reflects extensive seawater Fe removal during the development of more widespread euxinia. This led to enhanced

SUBMITTER: Qiu Z 

PROVIDER: S-EPMC12822635 | biostudies-literature | 2026 Jan

REPOSITORIES: biostudies-literature