Triple oxygen isotope evidence for limited mid-Proterozoic primary productivity

• Published in: Nature (London) 2018-07, Vol.559 (7715), p.613-616
• Main Authors: Crockford, Peter W., Hayles, Justin A., Bao, Huiming, Planavsky, Noah J., Bekker, Andrey, Fralick, Philip W., Halverson, Galen P., Bui, Thi Hao, Peng, Yongbo, Wing, Boswell A.
• Format: Article
• Language: English
• Subjects: 704/47; 704/47/4112; 704/47/4113; Anthropogenic factors; Atmosphere; Atmosphere - chemistry; Atmospheric models; Basins (Geology); Biological research; Biosphere; Carbon dioxide; Carbon Dioxide - analysis; Carbon dioxide atmospheric concentrations; Chemical properties; Earth; Ecosystem; Ecosystems; Fractionation; Geologic Sediments - chemistry; Geologic Sediments - microbiology; Geology; History, Ancient; Humanities and Social Sciences; Ice ages; Isotopes; Letter; Measurement; multidisciplinary; Ontario; Oxidation; Oxygen; Oxygen - analysis; Oxygen - metabolism; Oxygen isotopes; Oxygen Isotopes - analysis; Oxygen Isotopes - metabolism; Partial Pressure; Period 2 protein; Phanerozoic Eon; Photosynthesis; Primary productivity (Biology); Probability; Production management; Productivity; Science; Science (multidisciplinary); Sediments; Stratosphere; Sulfates; Sulfates - analysis; Sulfates - metabolism; Sulfides - analysis; Sulfides - metabolism; Sulfur; Sulfur - analysis; Sulfur - metabolism; Sulfur compounds; Sulfur Isotopes - analysis; Sulfur Isotopes - metabolism
• ISSN: 0028-0836; 1476-4687
• DOI: 10.1038/s41586-018-0349-y

The global biosphere is commonly assumed to have been less productive before the rise of complex eukaryotic ecosystems than it is today 1 . However, direct evidence for this assertion is lacking. Here we present triple oxygen isotope measurements (∆ 17 O) from sedimentary sulfates from the Sibley basin (Ontario, Canada) dated to about 1.4 billion years ago, which provide evidence for a less productive biosphere in the middle of the Proterozoic eon. We report what are, to our knowledge, the most-negative ∆ 17 O values (down to −0.88‰) observed in sulfates, except for those from the terminal Cryogenian period 2 . This observation demonstrates that the mid-Proterozoic atmosphere was distinct from what persisted over approximately the past 0.5 billion years, directly reflecting a unique interplay among the atmospheric partial pressures of CO 2 and O 2 and the photosynthetic O 2 flux at this time 3 . Oxygenic gross primary productivity is stoichiometrically related to the photosynthetic O 2 flux to the atmosphere. Under current estimates of mid-Proterozoic atmospheric partial pressure of CO 2 (2–30 times that of pre-anthropogenic levels), our modelling indicates that gross primary productivity was between about 6% and 41% of pre-anthropogenic levels if atmospheric O 2 was between 0.1–1% or 1–10% of pre-anthropogenic levels, respectively. When compared to estimates of Archaean 4 – 6 and Phanerozoic primary production 7 , these model solutions show that an increasingly more productive biosphere accompanied the broad secular pattern of increasing atmospheric O 2 over geologic time 8 . Triple oxygen isotope measurements of 1.4-billion-year-old sedimentary sulfates reveal a unique mid-Proterozoic atmosphere and demonstrate that gross primary productivity in the mid-Proterozoic was between 6% and 41% of pre-anthropogenic levels.