Biogeochemical Cycles & Geobiology

Three-stage Formation of Cap Carbonates after Marinoan Snowball Glaciation Consistent with Depositional Timescales and Geochemistry

By Keith Cowing

Status Report

astro-ph.EP

August 20, 2024

Filed under astro-ph.EP, atmosphere, biogeochemical cycles, cap carbonation, climate, galcier, geochemistry, icy world, Marinoan Snowball Glaciation, snowball earth

Three-stage Formation of Cap Carbonates after Marinoan Snowball Glaciation Consistent with Depositional Timescales and Geochemistry — Model benchmark against the modern climate system. Histograms show the results for observable variables from 1000 model runs where uncertain parameters are sampled. The vertical shaded regions are the measured or assumed modern values. (a, b, c) We assume the pre-industrial modern climate had 280 ppm atmospheric CO2, 285 K surface temperature, and 8.2 ocean pH. (d) The calcite and aragonite saturation states of the modern ocean vary from over 5 at the surface to below 0.5 in the deep ocean (Pilson 2012). (e) Estimates of continental carbonate weathering are from Hartmann et al. (2009), continental silicate weathering are from Moon et al. (2014), and seafloor weathering are from Coogan & Gillis (2013) and Krissansen-Totton et al. (2018). (f) Estimates of neritic carbonate deposition are from Iglesias-Rodriguez et al. (2002) and pore-space deposition are from Gillis & Coogan (2011) and Krissansen-Totton et al. (2018). — astro-ph.EP

At least two global “Snowball Earth” glaciations occurred during the Neoproterozoic Era (1000-538.8 million years ago). Post-glacial surface environments during this time are recorded in cap carbonates: layers of limestone or dolostone that directly overlie glacial deposits.

Postulated environmental conditions that created the cap carbonates lack consensus largely because single hypotheses fail to explain the cap carbonates’ global mass, depositional timescales, and geochemistry of parent waters.

Here, we present a global geologic carbon cycle model before, during, and after the second glaciation (i.e. the Marinoan) that explains cap carbonate characteristics.

We find a three-stage process for cap carbonate formation: (1) low-temperature seafloor weathering during glaciation generates deep-sea alkalinity; (2) vigorous post-glacial continental weathering supplies alkalinity to a carbonate-saturated freshwater layer, rapidly precipitating cap carbonates; (3) mixing of post-glacial meltwater with deep-sea alkalinity prolongs cap carbonate deposition. We suggest how future geochemical data and modeling refinements could further assess our hypothesis.

Trent B. Thomas, David C. Catling

Comments: Main text is 30 pages double spaced. 8 figures, 1 table. Supplementary Material included at end of file. Published in Nature Communications
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Atmospheric and Oceanic Physics (physics.ao-ph); Geophysics (physics.geo-ph)
Cite as: arXiv:2408.10179 [astro-ph.EP] (or arXiv:2408.10179v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2408.10179
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Journal reference: Nat Commun 15, 7055 (2024)
Related DOI:
https://doi.org/10.1038/s41467-024-51412-8
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Submission history
From: Trent Thomas
[v1] Mon, 19 Aug 2024 17:39:18 UTC (7,865 KB)
https://arxiv.org/abs/2408.10179
Astrobiology,

Keith Cowing

Explorers Club Fellow, ex-NASA Space Station Payload manager/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Na’Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp veteran, (he/him) 🖖🏻

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