Affiliation:
1. Department of Animal and Plant Sciences, University of SheffieldSheffield S10 2TN, UK
2. Centre for Atmospheric Science, Department of Chemistry, University of CambridgeCambridge CB2 1EW, UK
3. National Centre of Atmospheric Science (NCAS), Atmospheric Chemistry Modelling Support Unit, University of CambridgeCambridge CB2 1EW, UK
Abstract
The discovery of mutated palynomorphs in end-Permian rocks led to the hypothesis that the eruption of the Siberian Traps through older organic-rich sediments synthesized and released massive quantities of organohalogens, which caused widespread O
3
depletion and allowed increased terrestrial incidence of harmful ultraviolet-B radiation (UV-B, 280–315 nm; Visscher
et al
. 2004
Proc. Natl Acad. Sci. USA
101
, 12 952–12 956). Here, we use an extended version of the Cambridge two-dimensional chemistry–transport model to evaluate quantitatively this possibility along with two other potential causes of O
3
loss at this time: (i) direct effects of HCl release by the Siberian Traps and (ii) the indirect release of organohalogens from dispersed organic matter. According to our simulations, CH
3
Cl released from the heating of coals alone caused comparatively minor O
3
depletion (5–20% maximum) because this mechanism fails to deliver sufficiently large amounts of Cl into the stratosphere. The unusual explosive nature of the Siberian Traps, combined with the direct release of large quantities of HCl, depleted the model O
3
layer in the high northern latitudes by 33–55%, given a main eruptive phase of less than or equal to 200 kyr. Nevertheless, O
3
depletion was most extensive when HCl release from the Siberian Traps was combined with massive CH
3
Cl release synthesized from a large reservoir of dispersed organic matter in Siberian rocks. This suite of model experiments produced column O
3
depletion of 70–85% and 55–80% in the high northern and southern latitudes, respectively, given eruption durations of 100–200 kyr. On longer eruption time scales of 400–600 kyr, corresponding O
3
depletion was 30–40% and 20–30%, respectively. Calculated year-round increases in total near-surface biologically effective (BE) UV-B radiation following these reductions in O
3
layer range from 30–60 (kJ m
−2
d
−1
)
BE
up to 50–100 (kJ m
−2
d
−1
)
BE
. These ranges of daily UV-B doses appear sufficient to exert mutagenic effects on plants, especially if sustained over tens of thousands of years, unlike either rising temperatures or SO
2
concentrations.
Subject
General Physics and Astronomy,General Engineering,General Mathematics
Cited by
104 articles.
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