A diurnal carbon engine explains 13C-enriched carbonates without increasing the global production of oxygen

Emily C. Geyman, Adam C. Maloof

Research output: Contribution to journalArticlepeer-review

47 Scopus citations


In the past 3 billion years, significant volumes of carbonate with high carbon-isotopic ([Formula: see text]C) values accumulated on shallow continental shelves. These deposits frequently are interpreted as records of elevated global organic carbon burial. However, through the stoichiometry of primary production, organic carbon burial releases a proportional amount of [Formula: see text], predicting unrealistic rises in atmospheric [Formula: see text] during the 1 to 100 million year-long positive [Formula: see text]C excursions that punctuate the geological record. This carbon-oxygen paradox assumes that the [Formula: see text]C of shallow water carbonates reflects the [Formula: see text]C of global seawater-dissolved inorganic carbon (DIC). However, the [Formula: see text]C of modern shallow-water carbonate sediment is higher than expected for calcite or aragonite precipitating from seawater. We explain elevated [Formula: see text]C in shallow carbonates with a diurnal carbon cycle engine, where daily transfer of carbon between organic and inorganic reservoirs forces coupled changes in carbonate saturation ([Formula: see text]) and [Formula: see text]C of DIC. This engine maintains a carbon-cycle hysteresis that is most amplified in shallow, sluggishly mixed waters with high rates of photosynthesis, and provides a simple mechanism for the observed [Formula: see text]C-decoupling between global seawater DIC and shallow carbonate, without burying organic matter or generating O2.

Original languageEnglish (US)
Pages (from-to)24433-24439
Number of pages7
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number49
StatePublished - Dec 3 2019

All Science Journal Classification (ASJC) codes

  • General


  • carbon isotopes
  • carbonates
  • chemostratigraphy
  • paleoclimate


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