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Basin-scale sulfur cycling driven by volcanism in Southern high latitudes during the Oceanic Anoxic Event 2.

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Title: Basin-scale sulfur cycling driven by volcanism in Southern high latitudes during the Oceanic Anoxic Event 2.
Authors: Zeng, Zhiyu1 (AUTHOR), Xu, Yilun1 (AUTHOR), Yao, Weiqi1 (AUTHOR) yaowq@sustech.edu.cn
Source: Geochimica et Cosmochimica Acta. Jun2026, Vol. 423, p396-406. 11p.
Subjects: Sulfur cycle, Volcanism, Cretaceous Period, Igneous provinces, Sulfur isotopes, Ocean temperature, Iron sulfides, Anoxic waters
Geographic Terms: Southern Hemisphere
Abstract: The Oceanic Anoxic Event 2 (OAE2) represents the episode of large-scale ocean oxygen loss under extreme warmth in the late Cretaceous. The initiation of the OAE2 has been attributed to massive volcanic carbon emissions related to the emplacement of Large Igneous Provinces (LIPs), accompanied by significant perturbations in biogeochemical cycles of carbon, oxygen, and sulfur. Given the lower sulfate concentration in the Cretaceous ocean than it is today, its residence time was shorter under comparable fluxes, increasing the likelihood of spatial heterogeneity in the marine sulfur cycle. Since most existing data of seawater sulfate S-isotope ratio (δ34S) for the OAE2 are reported from localities distant from LIPs, our understanding of the effects of volcanism on regional sulfur cycling and climate warming remains poorly constrained. In this study, we present marine barite δ34S and TEX 86 -derived sea-surface temperature (SST) records across the OAE2 from the Mentelle Basin, which was proximal to the active Kerguelen LIP (KLIP) in Southern high latitudes. Our result shows a basin-scale ∼5‰ decrease in seawater sulfate δ34S during the OAE2, followed by a recovery to the higher-than-pre-excursion value in the post-OAE2. The simple box model attributes the δ34S decline to a volcanic pulse of 6.96 × 1012 mol isotopically light sulfur released into the ocean within 50 thousand years, which is approximately threefold of the background flux. The subsequent δ34S overshoot requires a coeval increase in pyrite burial flux by 10%, indicating a modest expansion of anoxia in the Mentelle Basin. Meanwhile, the TEX 86 -derived SST documents prolonged warmth persisting into the post-OAE2, providing an independent constraint on thermal forcing during the recovery phase. Sustained elevated SST in the high-latitude Southern Hemisphere would not only have promoted basin-scale deoxygenation and pyrite burial beyond the initial volcanic perturbation, but also reduced the meridional SST gradient and efficiency of poleward heat redistribution, thereby acting as positive feedback that helped sustain global warming. These findings reveal the response of basin-scale sulfur cycling and persistent warmth to volcanic activities in the high-latitude ocean across the OAE2. [ABSTRACT FROM AUTHOR]
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Abstract:The Oceanic Anoxic Event 2 (OAE2) represents the episode of large-scale ocean oxygen loss under extreme warmth in the late Cretaceous. The initiation of the OAE2 has been attributed to massive volcanic carbon emissions related to the emplacement of Large Igneous Provinces (LIPs), accompanied by significant perturbations in biogeochemical cycles of carbon, oxygen, and sulfur. Given the lower sulfate concentration in the Cretaceous ocean than it is today, its residence time was shorter under comparable fluxes, increasing the likelihood of spatial heterogeneity in the marine sulfur cycle. Since most existing data of seawater sulfate S-isotope ratio (δ34S) for the OAE2 are reported from localities distant from LIPs, our understanding of the effects of volcanism on regional sulfur cycling and climate warming remains poorly constrained. In this study, we present marine barite δ34S and TEX 86 -derived sea-surface temperature (SST) records across the OAE2 from the Mentelle Basin, which was proximal to the active Kerguelen LIP (KLIP) in Southern high latitudes. Our result shows a basin-scale ∼5‰ decrease in seawater sulfate δ34S during the OAE2, followed by a recovery to the higher-than-pre-excursion value in the post-OAE2. The simple box model attributes the δ34S decline to a volcanic pulse of 6.96 × 1012 mol isotopically light sulfur released into the ocean within 50 thousand years, which is approximately threefold of the background flux. The subsequent δ34S overshoot requires a coeval increase in pyrite burial flux by 10%, indicating a modest expansion of anoxia in the Mentelle Basin. Meanwhile, the TEX 86 -derived SST documents prolonged warmth persisting into the post-OAE2, providing an independent constraint on thermal forcing during the recovery phase. Sustained elevated SST in the high-latitude Southern Hemisphere would not only have promoted basin-scale deoxygenation and pyrite burial beyond the initial volcanic perturbation, but also reduced the meridional SST gradient and efficiency of poleward heat redistribution, thereby acting as positive feedback that helped sustain global warming. These findings reveal the response of basin-scale sulfur cycling and persistent warmth to volcanic activities in the high-latitude ocean across the OAE2. [ABSTRACT FROM AUTHOR]
ISSN:00167037
DOI:10.1016/j.gca.2026.03.023