Climatic and Biogeochemical Effects of a Galactic Gamma-Ray Burst

Astrophysics, abstract
astro-ph/0503625

From: Adrian Melott [view email]

Date: Tue, 29 Mar 2005 16:18:37 GMT   (226kb)

It is likely that one or more gamma-ray bursts within our galaxy have
strongly irradiated the Earth with X-ray and gamma-ray photons in the last Gy.
This produces significant atmospheric constituent ionization and dissociation,
resulting in ozone depletion and DNA-damaging ultraviolet solar flux reaching
the surface for up to a decade. Here we show the first detailed computation of
two other significant effects. Visible opacity of NO2 is sufficient to reduce
solar energy at the surface up to a few percent, with the greatest effect at
the poles. This may be a sufficient climate perturbation to initiate
glaciation. Rainout of dilute nitric acid is a primary atmospheric removal
mechanism for odd nitrogen compounds, which can temporarily boost fertility in
terrestrial and shallow water ecosystems. These results support the hypothesis
that the late Ordovician mass extinction may have been initiated by a gamma-ray
burst, in that it was accompanied by glaciation, 13C isotope abundance
excursions, and followed by significantly expanded terrestrial flora.

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