Explosive volcanism as a key driver of the late Paleozoic ice age

Abstract

Atmospheric CO 2 exerts a robust and well-documented control on Earth's climate, but the timing of glaciation during the late Paleozoic Ice Age (LPIA; ca. 360-260 Ma) is inconsistent with pCO 2 reconstructions, hinting at another factor. Stratospheric volcanic aerosols produce a large but temporary negative radiative forcing under modern conditions. Here we examine explosive volcanism over 200 m.y. of Earth history to show that the LPIA corresponded with a sustained increase in volcanism in both tropical and extratropical latitudes. A major peak in explosive volcanism at ca. 300 Ma likely corresponded to stratospheric sulfur-injecting eruptions at least three to eight times more frequent than at present. This level of volcanism created a steady, negative radiative forcing potentially sufficient to initiate and, most critically, sustain icehouse conditions, even under increasing levels of pCO 2 , and helps resolve discrepancies between glacial timing and CO 2 records. Accounting for the radiative forcing effects of CO 2 and sulfate indicates that both are required to explain the LPIA, with sulfate producing an especially strong effect at peak icehouse ca. 298-295 Ma. Frequent explosive volcanism would have increased atmospheric acidity, enhancing the reactivity of iron in abundant volcanic ash and glacially generated mineral dust, thus strengthening the climate impact of volcanism through a marine biological pump further primed by feedback with glaciation.

Influence of temporally varying weatherability on CO<sub>2</sub>-climate coupling and ecosystem change in the late Paleozoic

“…Declining pCO 2 toward a nadir in the earliest Permian is also consistent with a renewed increase in the geographic distribution of glacial deposits in Gondwana beginning in the late Pennsylvanian and peaking in the earliest Permian ( Fig. 2b; Soreghan et al, 2019).…”

“…S1 for error bars on individual CO 2 estimates and the 95 % CI, and see Richey et al (2020) (http://doi.org/10.25338/B8S90Q) for the full dataset. (b) Multiproxy CO 2 record and individual estimates (this study and agerecalibrated values by Montañez et al, 2016; n = 165), documented glacial deposits (Soreghan et al, 2019), occurrence of peats (coal), and best estimate of timing (and uncertainties) of magmatic episodes: 1a = Tarim 1, China (∼ 300 Ma); 1b = Tarim 2 (292-287, peak ∼ 290 Ma); 1c = Tarim 3 (284-272, peak ∼ 280 Ma; Chen and Xu, 2019); 2 = Skagerrak-centered, NW Europe (297.5 ± 3.8 Ma; Torsvik et al, 2008); 3a = Panjal Traps, NW India (289 ± 3 Ma; Shellnutt, 2018); 3b = Qiangtang Traps, Tibet (283 ± 2 Ma; Zhai et al, 2013); 4 = Choiyoi, W Argentina (beginning 286.5 ± 2.3 Ma, continuing for up to 39 Myr; Sato et al, 2015). Trend lines are as in (a); dashed intervals across the Carboniferous-Permian boundary (298.9 Ma) indicate overlap of the two LOESS trend lines.…”

“…A 10 Myr CO 2 nadir (∼ 180 to < 400 ppm) characterizes the first two stages (Asselian and Sakmarian; 298.9 to 290.1 Ma) of the early Permian, overlaps with the peak occurrence of glacial deposits in the LPIA (gray boxes in Fig. 2b; Soreghan et al, 2019), and defines a second interval of anomalously high O 2 /CO 2 ratios (up to 970 ppm; Fig. 3a).…”

“…Additionally, the burial of substantial organic matter as peat in swamp environments prone to preservation (ultimately as coal) during the Pennsylvanian would have partitioned global CO 2 consumption between silicate weathering and organic carbon burial, further driving steady-state pCO 2 lower (D'Antonio et al, 2019;Ibarra et al, 2019). Our modeling, however, assumes a constant pre-Hercynian solid Earth degassing through the study interval, and it does not account for increased magmatic CO 2 during Hercynian arc-continent collision and potential widespread eruptive volcanism in the late Carboniferous (Soreghan et al, 2019), both of which could have increased steady-state CO 2 .…”

AGU Centennial Grand Challenge: Volcanoes and Deep Carbon Global CO2 Emissions From Subaerial Volcanism—Recent Progress and Future Challenges

“…Whether increased volcanism drives long‐term global cooling or warming continues to be debated, not surprising because increased arc magmatism will cause outpour of CO 2 but then weathering of arc rocks sequesters atmospheric CO 2 (Lee & Dee, ). Recently, Soreghan et al () proposed that the late Paleozoic Ice Age (360–260 Ma) correlates with an episode of increased explosive volcanism that injected sulfate aerosol into the stratosphere at rates at least 8 times higher than today and also caused additional CO 2 drawdown due to fertilization of the oceans resulting in increased biological productivity. While volcanic sulfate aerosol forcing is an important impact of explosive volcanism, an aspect usually ignored in the connections between volcanism and climate is the fact that volcanoes degas CO 2 without eruptions and that in fact only about 1–2% of CO 2 is released during eruptions globally compared to the amount released during passive degassing (Fischer et al, ; Werner et al, ).…”