Past climate change - Climate Change: Biological and Human Aspects - page 83

If the Siberian Traps volcanic activity were not enough, it has been suggested that
the resulting global warming from volcanic carbon dioxide may have been enhanced
by large releases of methane from the oceans. Methane hydrates (or clathrates) exist
in considerable quantities off the continental shelf (see section 6.6.4 on methane
hydrates, and the Toarcian and Eocene warming events below). Methane hydrate
stability depends on pressure and temperature: reduce the former or increase the latter
and they quickly dissociate, releasing methane gas, which (as noted in Chapter 1)
is a powerful greenhouse gas. At the end of the Permian if volcanic carbon dioxide
(or carbon dioxide or methane from magma-warmed, organic-rich sediments) had
warmed the planet then some of this heat would have been conveyed to oceanic deep
waters and possibly destabilised methane hydrates. The methane would have further
enhanced any global warming, so further stressing ecosystems globally.
As if this methane enhancement were not enough there is (somewhat speculative)
evidence to suggest that much of the extinction 'could have occurred in a single
bad day' (Ward et al., 2000). Geological strata, where the Karoo Basin subsequently
formed in South Africa, imply that a forest was literally stripped away in a very short
time (Ward et al., 2000). Could it be, in addition to the Siberian Traps vulcanism
generating global cooling and then warming, and the consequential oceanic methane
release, that there was an asteroidal or cometary impact (Becker et al., 2001; Jin et al.,
2000)? In 2004 an Australian/US team of researchers reported their discovery of an
impact crater that they say may have been responsible for the end-Permian extinction.
Located off the north-west Australian coast (due west of Roebuck Bay and north of
De Grey) the crater may be about 100 km in diameter but this estimate is tentative
due to erosion (Becker et al., 2004). Even so, it is the same order of magnitude as the
Chicxulub crater in Yucatan, Mexico, which is thought to have played a part in the
Cretaceous-Tertiary dinosaur extinction (see section 3.3.8).
Of course, even without evoking climate change, there were other, minor (non-
global) effects of the Siberian Traps vulcanism. Being in or around Siberia at the
time would not have been healthy simply because of the widespread volcanic activity.
Another minor effect (comparatively speaking) would have been the destruction of
the ozone layer, caused by gas emissions. Chlorine and fluorine gases are released
by almost all volcanic eruptions and they destroy the ozone layer. Without the ozone
layer, harmful ultraviolet rays can kill exposed terrestrial organisms, so contributing
to the mass extinction.
For many years the cause of the end-Permian mass extinction appeared to involve
'a tangled web rather than a single mechanism' (Erwin, 1994). Yet we know that
much of life was simply wiped out, but not all life. Indeed, for a brief time it appears
that fungi flourished. There is a fungal spike in the geological record around the onset
of the Siberian Traps eruption, supposedly due to fungi living on dead and rotting
vegetation. (A somewhat similar fungal spike has been identified in strata associated
with the Cretaceous-Tertiary extinction: see below; only 'somewhat' because that
fungal spike did not take place at the onset of the vulcanism that led up to that
extinction, but is associated with an asteroid strike.)
Three papers published in 2011 provide some clues for a single principal cause.
The first was in Nature Geoscience and written by Stephen Grasby, Hamed Sanei and
Benoit Beauchamp. They discovered that many end-Permian strata contained char