TY - JOUR
T1 - Perspectives on Proterozoic surface ocean redox from iodine contents in ancient and recent carbonate
AU - Hardisty, Dalton S.
AU - Lu, Zunli
AU - Bekker, Andrey
AU - Diamond, Charles W.
AU - Gill, Benjamin C.
AU - Jiang, Ganqing
AU - Kah, Linda C.
AU - Knoll, Andrew H.
AU - Loyd, Sean J.
AU - Osburn, Magdalena R.
AU - Planavsky, Noah J.
AU - Wang, Chunjiang
AU - Zhou, Xiaoli
AU - Lyons, Timothy W.
N1 - Funding Information:
TL, ZL, and DH thank NSF EAR-1349252. ZL further thanks OCE-1232620. DH, ZL, and TL acknowledge further funding from a NASA Early Career Collaboration Award. TL, AB, NP, DH, and AK thank the NASA Astrobiology Institute (under Cooperative Agreement No. NNA15BB03A issued through the Science Mission Directorate). TL and NP received support from the Earth-Life Transitions Program of the National Science Foundation (under Award No. EAR-1338299). AB acknowledges support from NSF grant EAR-05-45484 and an NSERC Discovery and Accelerator Grants. CW acknowledges support from NSFC grant 40972021. We also thank Peter Swart for providing the Unda and Clino drill cores, which was supported by NSF funding (OCE-8917295) to PS. We also thank Masha Prokopenko for contribution of carbon isotope values from some GBB short cores. The authors also thank two reviewers for insightful comments that greatly improved this work.
Publisher Copyright:
© 2017 Elsevier B.V.
PY - 2017/4/1
Y1 - 2017/4/1
N2 - The Proterozoic Eon hosted the emergence and initial recorded diversification of eukaryotes. Oxygen levels in the shallow marine settings critical to these events were lower than today's, although how much lower is debated. Here, we use concentrations of iodate (the oxidized iodine species) in shallow-marine limestones and dolostones to generate the first comprehensive record of Proterozoic near-surface marine redox conditions. The iodine proxy is sensitive to both local oxygen availability and the relative proximity to anoxic waters. To assess the validity of our approach, Neogene–Quaternary carbonates are used to demonstrate that diagenesis most often decreases and is unlikely to increase carbonate-iodine contents. Despite the potential for diagenetic loss, maximum Proterozoic carbonate iodine levels are elevated relative to those of the Archean, particularly during the Lomagundi and Shuram carbon isotope excursions of the Paleo- and Neoproterozoic, respectively. For the Shuram anomaly, comparisons to Neogene–Quaternary carbonates suggest that diagenesis is not responsible for the observed iodine trends. The baseline low iodine levels in Proterozoic carbonates, relative to the Phanerozoic, are linked to a shallow oxic–anoxic interface. Oxygen concentrations in surface waters would have at least intermittently been above the threshold required to support eukaryotes. However, the diagnostically low iodine data from mid-Proterozoic shallow-water carbonates, relative to those of the bracketing time intervals, are consistent with a dynamic chemocline and anoxic waters that would have episodically mixed upward and laterally into the shallow oceans. This redox instability may have challenged early eukaryotic diversification and expansion, creating an evolutionary landscape unfavorable for the emergence of animals.
AB - The Proterozoic Eon hosted the emergence and initial recorded diversification of eukaryotes. Oxygen levels in the shallow marine settings critical to these events were lower than today's, although how much lower is debated. Here, we use concentrations of iodate (the oxidized iodine species) in shallow-marine limestones and dolostones to generate the first comprehensive record of Proterozoic near-surface marine redox conditions. The iodine proxy is sensitive to both local oxygen availability and the relative proximity to anoxic waters. To assess the validity of our approach, Neogene–Quaternary carbonates are used to demonstrate that diagenesis most often decreases and is unlikely to increase carbonate-iodine contents. Despite the potential for diagenetic loss, maximum Proterozoic carbonate iodine levels are elevated relative to those of the Archean, particularly during the Lomagundi and Shuram carbon isotope excursions of the Paleo- and Neoproterozoic, respectively. For the Shuram anomaly, comparisons to Neogene–Quaternary carbonates suggest that diagenesis is not responsible for the observed iodine trends. The baseline low iodine levels in Proterozoic carbonates, relative to the Phanerozoic, are linked to a shallow oxic–anoxic interface. Oxygen concentrations in surface waters would have at least intermittently been above the threshold required to support eukaryotes. However, the diagnostically low iodine data from mid-Proterozoic shallow-water carbonates, relative to those of the bracketing time intervals, are consistent with a dynamic chemocline and anoxic waters that would have episodically mixed upward and laterally into the shallow oceans. This redox instability may have challenged early eukaryotic diversification and expansion, creating an evolutionary landscape unfavorable for the emergence of animals.
KW - Bahamas
KW - Proterozoic oxygen
KW - Shuram isotope anomaly
KW - carbonate diagenesis
KW - iodine
KW - metazoan evolution
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U2 - 10.1016/j.epsl.2017.01.032
DO - 10.1016/j.epsl.2017.01.032
M3 - Article
AN - SCOPUS:85012927399
SN - 0012-821X
VL - 463
SP - 159
EP - 170
JO - Earth and Planetary Science Letters
JF - Earth and Planetary Science Letters
ER -