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Limited oxygen production in the Mesoarchean ocean.


ABSTRACT: The Archean Eon was a time of predominantly anoxic Earth surface conditions, where anaerobic processes controlled bioessential element cycles. In contrast to "oxygen oases" well documented for the Neoarchean [2.8 to 2.5 billion years ago (Ga)], the magnitude, spatial extent, and underlying causes of possible Mesoarchean (3.2 to 2.8 Ga) surface-ocean oxygenation remain controversial. Here, we report ?15N and ?13C values coupled with local seawater redox data for Mesoarchean shales of the Mozaan Group (Pongola Supergroup, South Africa) that were deposited during an episode of enhanced Mn (oxyhydr)oxide precipitation between ?2.95 and 2.85 Ga. Iron and Mn redox systematics are consistent with an oxygen oasis in the Mesoarchean anoxic ocean, but ?15N data indicate a Mo-based diazotrophic biosphere with no compelling evidence for a significant aerobic nitrogen cycle. We propose that in contrast to the Neoarchean, dissolved O2 levels were either too low or too limited in extent to develop a large and stable nitrate reservoir in the Mesoarchean ocean. Since biological N2 fixation was evidently active in this environment, the growth and proliferation of O2-producing organisms were likely suppressed by nutrients other than nitrogen (e.g., phosphorus), which would have limited the expansion of oxygenated conditions during the Mesoarchean.

SUBMITTER: Ossa Ossa F 

PROVIDER: S-EPMC6452703 | biostudies-literature | 2019 Apr

REPOSITORIES: biostudies-literature

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Limited oxygen production in the Mesoarchean ocean.

Ossa Ossa Frantz F   Hofmann Axel A   Spangenberg Jorge E JE   Poulton Simon W SW   Stüeken Eva E EE   Schoenberg Ronny R   Eickmann Benjamin B   Wille Martin M   Butler Mike M   Bekker Andrey A  

Proceedings of the National Academy of Sciences of the United States of America 20190320 14


The Archean Eon was a time of predominantly anoxic Earth surface conditions, where anaerobic processes controlled bioessential element cycles. In contrast to "oxygen oases" well documented for the Neoarchean [2.8 to 2.5 billion years ago (Ga)], the magnitude, spatial extent, and underlying causes of possible Mesoarchean (3.2 to 2.8 Ga) surface-ocean oxygenation remain controversial. Here, we report δ<sup>15</sup>N and δ<sup>13</sup>C values coupled with local seawater redox data for Mesoarchean  ...[more]

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