Carbon pump dynamics and limited organic carbon burial during <scp>OAE1a</scp>

Bauer, Kohen W.; McKenzie, N. Ryan; Bottini, Cinzia; Erba, Elisabetta; Crowe, Sean A.

doi:10.1111/gbi.12538

Cited by 2 publications

(1 citation statement)

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“…A limited impact of oxygen on OC burial efficiency provides support for the hypothesis that aerobic respiration drove Earth's oxygenation [64]. Additionally, our results question the assumption of enhanced OC burial efficiency in a seafloor underlying anoxic bottom waters, which is used in recent reconstructions of marine primary productivity during periods of extensive ocean anoxia in the Cretaceous, the Proterozoic and Archean Eon [65,66]. These studies suggest marine primary productivities that were 100 times (for the Proterozoic) to 1000 times (for the Archean) lower than today, mainly because of the assumption of enhanced OC burial efficiencies in anoxic oceans [66].…”

Section: Discussionsupporting

confidence: 63%

Exceptionally high respiration rates in the reactive surface layer of sediments underlying oxygen-deficient bottom waters

et al. 2023

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Organic carbon (OC) burial efficiency, which relates the OC burial rate to respiration in the seafloor, is a critical parameter in the reconstruction of past marine primary productivities. The current accepted theory is that sediments underlying oxygen-deficient (anoxic) bottom waters have low respiration rates and high OC burial efficiencies. By combining novel in situ measurements in anoxic basins with reaction-transport modelling, we demonstrate that sediments underlying anoxic bottom waters have much higher respiration rates than commonly assumed. A major proportion of the carbon respiration is concentrated in the top millimeter—the so-called ‘reactive surface layer’—which is likely a feature in approximately 15% of the coastal seafloor. When re-evaluating previously published data in light of our results, we conclude that the impact of bottom-water anoxia on OC burial efficiencies in marine sediments is small. Consequently, reconstructions of past marine primary productivity in a predominantly anoxic ocean based on OC burial rates might be underestimated by up to an order of magnitude.

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Section: Discussionsupporting

confidence: 63%

Exceptionally high respiration rates in the reactive surface layer of sediments underlying oxygen-deficient bottom waters

et al. 2023

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Siderite from the Tibetan Himalaya: Evidence for a low sulphate ocean during Oceanic Anoxic Event 1a (Early Aptian)

Meng,

Han,

et al. 2024

Sedimentology

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Mesozoic oceanic anoxic events were characterized by relatively low seawater sulphate concentrations ([]), which likely regulated the development and evolution of these major palaeoceanographic phenomena. However, there is little reliable sedimentary evidence for low [] in ancient marine waters and understanding of how such a seawater chemistry potentially impacted oceanic anoxic events is limited. This study presents an integrated sedimentological, mineralogical and geochemical investigation of the mineral siderite hosted in dark grey shale and sideritic concretions of Early Aptian (coeval with Oceanic Anoxic Event 1a) from the Tibetan Himalaya. Siderite is present throughout the section and possesses similar morphological characteristics whether in dark grey shale or concretions. Siderite can be present as disseminated and rhombic crystals formed during early diagenesis, or minor spherical crystals formed during late diagenesis. The evidence from redox elements, middle rare‐earth element bulge patterns and extremely low carbon‐isotope values of the sideritic concretions indicates that the iron carbonate was formed in the Fe‐reduction zones by the process of dissimilatory iron reduction. This process would have required conditions of low [], reducing environment, abundant iron and high alkalinity. Additionally, the coexistence of siderite and pyrite may indicate that dissimilatory iron reduction occurred close to the microbial sulphate reduction zone, with seawater [] hovering around the tipping point at which pyrite could form once seawater sulphate increased. Such an increase during Oceanic Anoxic Event 1a could have resulted from basalt–seawater interaction and associated enhanced continental weathering, and/or hydrothermal activity. This study's observations support the previous hypothesis that low [] for Oceanic Anoxic Event 1a was probably caused by massive gypsum burial in the proto‐South Atlantic. Subsequently, enhanced sulphate input could have promoted microbial sulphate reduction and accompanying oxidation of organic matter, which likely further enhanced nutrient recycling, increased primary productivity and organic‐carbon burial, leading to more oxygen consumption and expansion of oxygen minimum zones, as reconstructed for many oceanic anoxic events.

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Carbon pump dynamics and limited organic carbon burial during OAE1a

Cited by 2 publications

References 82 publications

Exceptionally high respiration rates in the reactive surface layer of sediments underlying oxygen-deficient bottom waters

Exceptionally high respiration rates in the reactive surface layer of sediments underlying oxygen-deficient bottom waters

Siderite from the Tibetan Himalaya: Evidence for a low sulphate ocean during Oceanic Anoxic Event 1a (Early Aptian)

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