Research ArticleCLIMATOLOGY

An early Cambrian greenhouse climate

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Science Advances  09 May 2018:
Vol. 4, no. 5, eaar5690
DOI: 10.1126/sciadv.aar5690
  • Fig. 1 Preservation of linguliformean brachiopods and Torellella from the Comley Limestones.

    (A) SEM and EDX analyses of pristine brachiopods preserve alternating compact and porous phosphatic laminae [(1) and (2)]; compact laminae comprise densely packed phosphatic spherules (3). Diagenetically sensitive elements, particularly Fe and Mg, are restricted to porous laminae (4). BSE, backscattered electron image. (B) SEM and EDX analyses of altered brachiopods may preserve laminar microstructure, but compact laminae phosphate has recrystallized to micrometer-scale prismatic crystals (3). Diagenetically sensitive elements indicative of alteration are found throughout altered specimens (4). (C) Pristine Torellella specimens comprise densely packed phosphatic spherules a few tens of nanometers in diameter (3).

  • Fig. 2 Early Cambrian δ18Ophos data from SSFs from the Comley Limestones.

    (A) In bulk analyses, altered subsets are isotopically lighter than the pristine counterparts from the same sample. Sample labels follow Table 1; error bars of 1 SD; δ18Ophos indicates trisilver phosphate analysis in which only phosphate oxygen isotopes were measured. (B) In situ (SIMS) data from linguliformean brachiopod specimens (sample Ad) show that porous laminae are consistently isotopically lighter than compact laminae. See data S1 and fig. S3. Box plots display the median and first and third quartiles, with the whiskers extending up to 1.5 times the interquartile range. All isotope data are reported relative to VSMOW.

  • Fig. 3 The Paleozoic phosphate δ18O record.

    Conodonts, blue squares; well-preserved linguliformean brachiopods, dark blue triangles; well-preserved Torellella samples, yellow circles; phosphate hardground data, purple hexagons). This trend is most pronounced in the earlier part of the Paleozoic. Data span a range of paleolatitudes and water depths. Our Cambrian data are essentially contemporaneous at approximately 513 Ma ago; for clarity, Torellella and phosphate hardground points have been shifted slightly on the age axis. All values are relative to VSMOW. See data S3.

  • Fig. 4 Cambrian isotopic SSTs in the context of Mesozoic and early Cenozoic greenhouse climate states.

    Cambrian data (black diamonds) from the δ18Ophos values of pristine SSF samples from the Comley Limestones. Data are plotted in 10° bins of the modulus of paleolatitude to illustrate latitudinal temperature variation irrespective of paleocontinental configuration. Plotted point data summarized in box plots displaying the median and first and third quartiles, with the whiskers extending up to 1.5 times the interquartile range. Cretaceous data, Cenomanian to Turonian; Paleogene data, Paleocene to Eocene. For references and literature data, see data S4. The modern latitudinal mean (black line) and range (gray envelope) data from the 2013 World Ocean Atlas 1° resolution data set (60).

  • Fig. 5 Early Cambrian mean annual SSTs, modeled by the FOAM GCM.

    The simulation was run under present-day orbital configurations with a CO2-equivalent greenhouse gas forcing of 32 PAL (see Materials and Methods and fig. S4). Black spot marks the position of our δ18Ophos data on Avalonia.

  • Table 1 Bulk (trisilver phosphate) δ18Ophos data from the Comley Limestones and SSTs exploring the influence of different values for δ18Osw.

    Temperatures calculated from Eq. 1 (22). T1 δ18Osw = −6.5‰, the most reasonable value; T2 δ18Osw = −6‰, assumes no latitudinal P-E effects; T3 δ18Osw = −1‰, the most commonly used Paleozoic value; T4 δ18Osw = −8‰, incorporating the maximum likely latitudinal P-E effect of −2‰. Temperature uncertainty (2 SD T1) calculated from δ18O measurement SDs, assuming that δ18Osw = −6.5‰. See data S1.

    SampleTriplicate mean δ18Ophos (‰ VSMOW)Triplicate 1 SD (‰ VSMOW)T1 (°C)T2 (°C)T3 (°C)T4 (°C)2 SD T1 (°C)
    Pristine brachiopods
    Aa-Br-L15.170.18202245131.6
    Ad-Br-L15.060.03202345140.3
    La2-Br-L13.930.22252850192.0
    Lb-Br-L14.630.14222547161.3
    Sa-Br-L14.620.15222547161.3
    Pristine Torellella
    Lb-To-To14.700.14222447151.3
    Sa-To-To14.590.07222547160.6
    Altered brachiopods
    La2-Br-D13.330.17283053211.5
    Lb-Br-D14.310.23242649172.1
    Sa-Br-D13.940.18252850191.7
    Sedimentary phosphate
    HG-A13.950.05252850190.5
    HG-A-DC14.070.21252750181.9
    HG-B12.770.09313355240.8
    HG-B-DC12.780.20313355241.8

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/4/5/eaar5690/DC1

    fig. S1. Paleogeographic and stratigraphic setting of the Comley Limestones (Avalonia, Cambrian Series 2).

    fig. S2. Examples of pristine and altered brachiopod and Torellella specimens.

    fig. S3. Box plots of ion microprobe (SIMS) data collected from pristine linguliformean brachiopods by tissue sampled.

    fig. S4. Global SST contour plots produced by early Cambrian FOAM GCM simulations for CO2-equivalent forcing of 32 PALs (see Materials and Methods).

    data S1. Triplicate trisilver phosphate isotope measurements.

    data S2. Processed ion microprobe (SIMS) data.

    data S3. Paleozoic phosphate δ18O data used to produce Fig. 3.

    data S4. Paleotemperature data used to produce Fig. 4.

    References (61124)

  • Supplementary Materials

    This PDF file includes:

    • fig. S1. Paleogeographic and stratigraphic setting of the Comley Limestones (Avalonia, Cambrian Series 2).
    • fig. S2. Examples of pristine and altered brachiopod and Torellella specimens.
    • fig. S3. Box plots of ion microprobe (SIMS) data collected from pristine linguliformean brachiopods by tissue sampled.
    • fig. S4. Global SST contour plots produced by early Cambrian FOAM GCM simulations for CO2-equivalent forcing of 32 PALs (see Materials and Methods).
    • References (61–124)

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    Other Supplementary Material for this manuscript includes the following:

    • data S1 (Microsoft Excel format). Triplicate trisilver phosphate isotope measurements.
    • data S2 (Microsoft Excel format). Processed ion microprobe (SIMS) data.
    • data S3 (Microsoft Excel format). Paleozoic phosphate δ18O data used to produce Fig. 3.
    • data S4 (Microsoft Excel format). Paleotemperature data used to produce Fig. 4.

    Files in this Data Supplement: