Low-phosphorus concentrations and important ferric hydroxide scavenging in Archean seawater

Author(s)

Rego, Eric Siciliano ; Busigny, Vincent ; Lalonde, Stefan V. ; Rossignol, Camille ; Babinski, Marly ; Philippot, Pascal

• Document type: Journal article
• Source: PNAS NEXUS; v. 2, n. 3, p. 7-pg., 2023-03-01.

Abstract

The availability of nutrients in seawater, such as dissolved phosphorus (P), is thought to have regulated the evolution and activity of microbial life in Earth's early oceans. Marine concentrations of bioavailable phosphorus spanning the Archean Eon remain a topic of debate, with variable estimates indicating either low (0.04 to 0.13 mu M P) or high (10 to 100 mu M P) dissolved P in seawater. The large uncertainty on these estimates reflects in part a lack of clear proxy signals recorded in sedimentary rocks. Contrary to some recent views, we show here that iron formations (IFs) are reliable recorders of past phosphorus concentrations and preserved a primary seawater signature. Using measured P and iron (Fe) contents in Neoarchean IF from Carajas (Brazil), we demonstrate for the first time a clear partitioning coefficient relationship in the P-Fe systematics of this IF, which, in combination with experimental and Archean literature data, permits us to constrain Archean seawater to a mean value of 0.063 +/- 0.05 mu M dissolved phosphorus. Our data set suggests that low-phosphorus conditions prevailed throughout the first half of Earth's history, likely as the result of limited continental emergence and marine P removal by iron oxyhydroxide precipitation, supporting prior suggestions that changes in ancient marine P availability at the end of the Archean modulated marine productivity, and ultimately, the redox state of Earth's early oceans and atmosphere. (AU)

• FAPESP's process: 15/16235-2 - The co-evolution of life and oxygen on early Earth: a South American perspective
• Grantee: Pascal Andre Marie Philippot
• Support Opportunities: Research Projects - SPEC Program
• FAPESP's process: 19/16271-0 - Element and isotope geochemistry from iron formations, carbonates and black shales: new insights into paleoredox conditions during the Neoarchean, Paleo- and Neoproterozoic in Brazil
• Grantee: Eric Siciliano Rego
• Support Opportunities: Scholarships abroad - Research Internship - Doctorate
• FAPESP's process: 19/16066-7 - Multiple isotope (O, S, Sr) constraints on the early Paleoproterozoic Great Oxidation Event from barite-bearing deposits of the Minas Supergroup, Minas Basin, Brazil
• Grantee: Camille Yann Rossignol
• Support Opportunities: Scholarships abroad - Research Internship - Post-doctor
• FAPESP's process: 18/05892-0 - Element and isotope geochemistry from iron formations and black shales: new insights into paleoredox conditions during the Paleo- and Neoproterozoic in North and Midwestern Brazil
• Grantee: Eric Siciliano Rego
• Support Opportunities: Scholarships in Brazil - Doctorate
• FAPESP's process: 18/02645-2 - Chronostratigraphy and isotopic tracing of the Paleoproterozoic Minas Supergroup
• Grantee: Camille Yann Rossignol
• Support Opportunities: Scholarships in Brazil - Post-Doctoral