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Mercury isotope signatures record photic zone euxinia in the Mesoproterozoic ocean
- Source :
- Proceedings of the National Academy of Sciences of the United States of America. 115(42)
- Publication Year :
- 2018
-
Abstract
- Photic zone euxinia (PZE) is a condition where anoxic, H(2)S-rich waters occur in the photic zone (PZ). PZE has been invoked as an impediment to the evolution of complex life on early Earth and as a kill mechanism for Phanerozoic mass extinctions. Here, we investigate the potential application of mercury (Hg) stable isotopes in marine sedimentary rocks as a proxy for PZE by measuring Hg isotope compositions in late Mesoproterozoic (∼1.1 Ga) shales that have independent evidence of PZE during discrete intervals. Strikingly, a significantly negative shift of Hg mass-independent isotope fractionation (MIF) was observed during euxinic intervals, suggesting changes in Hg sources or transformations in oceans coincident with the development of PZE. We propose that the negative shift of Hg MIF was most likely caused by (i) photoreduction of Hg(II) complexed by reduced sulfur ligands in a sulfide-rich PZ, and (ii) enhanced sequestration of atmospheric Hg(0) to the sediments by thiols and sulfide that were enriched in the surface ocean as a result of PZE. This study thus demonstrates that Hg isotope compositions in ancient marine sedimentary rocks can be a promising proxy for PZE and therefore may provide valuable insights into changes in ocean chemistry and its impact on the evolution of life.
- Subjects :
- Extinction event
Multidisciplinary
Stable isotope ratio
Chemistry
010501 environmental sciences
010502 geochemistry & geophysics
Early Earth
Mass-independent fractionation
01 natural sciences
Anoxic waters
Isotope fractionation
Environmental chemistry
Physical Sciences
Photic zone
Sedimentary rock
0105 earth and related environmental sciences
Subjects
Details
- ISSN :
- 10916490
- Volume :
- 115
- Issue :
- 42
- Database :
- OpenAIRE
- Journal :
- Proceedings of the National Academy of Sciences of the United States of America
- Accession number :
- edsair.doi.dedup.....5ea239c78ea2a489e91a27ea9a73f693