Coupled Nitrate and Phosphate Availability Facilitated the Expansion of Eukaryotic Life at Circa 1.56 Ga,Journal of Geophysical Research: Biogeosciences

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Coupled Nitrate and Phosphate Availability Facilitated the Expansion of Eukaryotic Life at Circa 1.56 Ga
Journal of Geophysical Research: Biogeosciences ( IF 3.7 ) Pub Date : 2020-04-07 , DOI: 10.1029/2019jg005487
Zhipeng Wang ₁ , Xinqiang Wang _{1,

2} , Xiaoying Shi _{1,

2} , Dongjie Tang _{2,

3} , Eva E. Stüeken _{4,

5} , Huyue Song ₆

Affiliation

Recent geochemical and paleontological studies have revealed a significant ocean oxygenation episode and an evolutionary leap of eukaryotes at the onset of the Mesoproterozoic. However, the potential role of nitrogen availability and its interaction with other nutrients in these environmental and biological events have not been investigated. Here we present an integrated study of nitrogen isotopes (δ¹⁵N), organic carbon isotopes (δ¹³C_org), and major and trace element concentrations from Member III of the Gaoyuzhuang Formation in the central North China Craton where the earliest macroscopic multicellular eukaryotic fossils were reported. The enrichments of redox‐sensitive elements (Mo, U, and V), coupled with Mo‐U covariations, δ¹³C_org, and I/(Ca + Mg), indicate that the Gaoyuzhuang Member III in the study area was deposited in largely suboxic‐anoxic environments with ephemeral occurrences of euxinia. These data reinforce previous inferences of a strongly redox stratified ocean during the early Mesoproterozoic, but a pulsed oxygenation event may have resulted in deepening of the chemocline. The high δ¹⁵N values from the study section are interpreted as a result of aerobic N cycling and the presence of a fairly stable nitrate pool in the surface oxic layer, possibly due to the combined effects of oxygenation and low primary productivity. Increased availability of nitrate could have contributed to the expansion of eukaryotic life at this time. However, our data also suggest that nitrate alone was not the only trigger. Instead, this evolutionary leap was likely facilitated by multiple environmental factors, including a rise in O₂ levels and increasing supplies of phosphorus and other bio‐essential trace elements.

更新日期：2020-04-22

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