Research ArticleGEOCHEMISTRY

Oceanic crustal carbon cycle drives 26-million-year atmospheric carbon dioxide periodicities

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Science Advances  14 Feb 2018:
Vol. 4, no. 2, eaaq0500
DOI: 10.1126/sciadv.aaq0500
  • Fig. 1 Schematic diagram showing oceanic crustal carbon cycle.

    Values indicate maximum and minimum carbon fluxes for the oceanic crustal carbon reservoir since 230 Ma. Downward-pointing arrows indicate that the carbon is sequestered into the crust or mantle. Upward-pointing arrows indicate carbon flux into the atmosphere. The ocean crust acts as either a sink or source of atmospheric carbon depending on its changing capacity to hold CO2 through time, subject to fluctuations in the age-area distribution of ocean crust and changes in bottom water temperature. The percentage of subducted carbon degassing into the atmosphere is not well known, and we show end-member fluxes based on 35 and 65% of subducted carbon escaping into the atmosphere.

  • Fig. 2 Atmospheric CO2 and tectonic model components.

    (A) Atmospheric CO2 through time with 68% confidence intervals (4). (B) Mid-ocean ridge length (orange) and subduction zone length (light blue) through time based on the study of Müller et al. (19). (C) Seafloor spreading rates (red) and convergence rates (dark blue) from the study of Müller et al. (19). (D) Power spectra with SEs of the data shown in (A) to (C), following the same color scheme.

  • Fig. 3 Oceanic crustal CO2 dependence on crustal age and bottom water temperature.

    (A) Oceanic crustal CO2 dependence on crustal age and oceanic bottom water temperature (20). (B) Estimated oceanic bottom water temperature through time and geological periods (see Materials and Methods), categorized into five temperature regimes. (C) Relationship between oceanic crustal CO2, crustal age, and bottom water temperature, based on best-fit log-linear relationships (see Materials and Methods).

  • Fig. 4 Global model grids.

    Modeled oceanic crustal CO2 content through time (left), bottom water temperature at the time of crustal accretion for any given parcel of ocean crust through time (middle), and paleo-age of the ocean crust (right) (19). Note that the increased crustal CO2 content at 50 and 100 Ma, relative to today, is driven mainly by increased ocean bottom water temperatures during crustal formation. Crustal CO2 content decreases from 100 to 200 Ma because of the presence of large areas of crust formed during the Late Carboniferous–Early Permian ice age associated with cool ocean bottom water temperatures (Fig. 3B) in the Panthalassic Ocean.

  • Fig. 5 Model outputs.

    (A) Oceanic crustal carbon content through time (blue) with SD (gray). (B) Carbon flux through time showing change in oceanic crustal carbon storage (blue), mid-ocean ridge degassing (purple), subduction flux into the atmosphere (red), and downgoing subduction carbon destined either for the deep mantle or the lithosphere (cyan) (12) assuming a simple 50-50 split. This ratio is not well known and may be anywhere between 1:3 and 3:1. Oceanic mantle carbon subduction flux is based on scaling today’s flux (12) with subduction zone length (Fig. 2B) through time (orange). (C) High-pass–filtered (cosine arch filter with 60-My width) atmospheric CO2 (black curve with gray error envelope) and modeled total carbon flux (green) including the relevant components shown in (B) (that is, all but the subducted carbon flux partitioned between the lithosphere and the convecting mantle); light red bars indicate bandwidths of the main periods of correlation between ~26-My period peaks in atmospheric CO2 and modeled carbon flux. (D) Spectral coherence of unfiltered atmospheric CO2 and modeled carbon flux time series (black, with 1 SD error bars; see text for discussion) peaks at 26 and 16 My. The three curves illustrate the coherence based on assuming that 35% (red), 50% (black), or 65% (blue) of subducted carbon degasses into the atmosphere. Note that the coherence at the 26-My period increases with decreasing subducted atmospheric carbon flux, whereas the remainder of the coherence plot is largely unaffected. (E) Power spectra of globally averaged trench migration speeds faster than 30 mm/year of eight global plate models with alternative reference frames [no net rotation model in light blue; models based on paleomagnetic data in dark blue, green, and dark yellow; and all other models based on hotspot tracks—see figure 4 in the study of Williams et al. (28) for details], revealing a dominant 26-My periodicity in trench migration.

Supplementary Materials

  • Supplementary Materials

    This PDF file includes:

    • fig. S1. Modeled oceanic crustal CO2 content through time.
    • fig. S2. Paleo-age of the ocean crust.
    • fig. S3. Modeled paleo-ocean bottom water temperature.

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