THE POTENTIAL BIOLOGICAL IMPACT OF EOLIAN DELIVERY OF REACTIVE IRON TO LATE PALEOZOIC ICEHOUSE SEAS

The biogeochemical impacts of dust-delivered iron to the open oceans are well recognized for Earth’s recent record but unexplored in deep time, despite recognition of large ancient dust fluxes, particularly during the late Paleozoic. Here, we report a unique Fe relationship for Upper Pennsylvanian mudrock of eolian origin that records lowstand (glacial) conditions within a carbonate buildup of western equatorial Pangaea (western US) well removed from other detrital inputs. During Pennsylvanian-Permian time, highlands and basins formed in western tropical Pangaea associated with Pangaean assembly. Strata within this region include thick dust (<10 µm) and loess (<63 µm) deposits in continental systems and marine carbonate in epeiric systems. One such system, the Midland basin, contains “Horseshoe Atoll,” an isolated carbonate buildup. This edifice consists of a series of Upper Pennsylvanian-Lower Permian reefal buildups devoid of siliciclastic material excepting that delivered via eolian input. In this system, reactive iron oxide phases were enriched without a corresponding increase in total Fe content. This association, which is atypical compared to modern marine sediments, riverine deposits, and soil-derived dust, suggests an enhancement of the reactivity of the internal Fe pool. Comparisons of our data with vast continental Pennsylvanian-Permian loess deposits reveal the same anomalous and enigmatic signal of enhanced iron reactivity. Regardless of the origin for the enhancement, our data in combination with independent evidence for high dust fluxes (glacial-stage dust fluxes ~400-4000 times those of interglacials) imply delivery of extraordinarily large amounts of biogeochemically reactive Fe to glacial-stage late Paleozoic seas. Integrating these results with aerosol modeling simulations for Early Permian paleogeography results in an estimated 14-110 Pg/yr of carbon fixation attributable to dust fertilization, ~2-20 times that of modern carbon fixation due to dust fertilization and ~0.2-2 times all modern marine carbon fixation. This result has major importance for the cycling of carbon and potential impacts on the Earth system for both the deep-time and modern worlds.