Subaerial volcanic trigger of ocean productivity recovery after the Toarcian Oceanic Anoxic Event

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Abstract
During the Toarcian Oceanic Anoxic Event (T-OAE, ~ 183 Ma), marine primary productivity (MPP) exhibited pronounced spatial heterogeneity, with limited organic carbon burial in many regions and unclear mechanisms for its subsequent recovery. Here, we present high resolution mercury isotopes, nitrogen and sulfur isotopes, iron speciation, and redox data from a marine sedimentary succession in the Neuquén Basin, Argentina, to investigate post T-OAE MPP recovery in a back-arc setting. Our results demonstrate that subaerial arc volcanism significantly intensified terrestrial chemical weathering (CIA from ~ 46 to ~ 70), enhancing terrestrial phosphorus input to the ocean. The resulting phosphorus supply exceeded nitrogen availability, triggering nitrogen fixation (δ¹⁵N bulk from + 13.81‰ to + 2.81‰), which effectively alleviated nitrogen limitation and sustained elevated MPP (TOC from < 1 wt% to 3.75 wt%). The increased organic carbon burial further promoted the upward migration of the sulfate reduction zone toward the sediment–water interface, enhancing sulfate supply and sulfur isotopic fractionation (as recorded by strongly negative δ³⁴S py values). This study demonstrates that regional arc volcanism acted as a key driver of post T-OAE marine productivity recovery by modulating weathering and nutrient cycling, providing new insights into the recovery of marine ecosystems after a major oceanic anoxic event.

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