Reduction of photosynthetically active radiation under extreme stratospheric aerosol loads
The recently published hypothesis that the Cretaceous-Tertiary extinctions might be caused by an obstruction of sunlight is tested by model calculations. First we compute the total mass of stratospheric aerosols under normal atmospheric conditions for four different (measured) aerosol size distributions and vertical profiles. For comparison, the stratospheric dust masses after four volcanic eruptions are also evaluated. Detailed solar radiative transfer calculations are then performed for artificially increased aerosol amounts until the postulated darkness scenario is obtained. Thus we find that a total stratospheric aerosol mass between 1 and 4 times 10/sup 1/ g is sufficient to reduce photosynthesis to 10/sup -3/ of normal. We also infer from this result tha the impact of a 0.4- to 3-km-diameter asteroid or a close encounter with a Halley-size comet may deposit that amount of particulates into the stratosphere. The darkness scenario of Alvarez et al. is thus shown to be a possible extinction mechanism, even with smaller size asteroids of comets than previously estimated.
- Research Organization:
- Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
- DOE Contract Number:
- W-7405-ENG-36
- OSTI ID:
- 6253858
- Report Number(s):
- LA-8938-MS; ON: DE81030506; TRN: 81-016889
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ASTEROIDS
ENVIRONMENTAL IMPACTS
COMETS
PHOTOSYNTHESIS
GLOBAL ASPECTS
AEROSOLS
COLLISIONS
MASS
MATHEMATICAL MODELS
SOLAR RADIATION
STRATOSPHERE
CHEMICAL REACTIONS
COLLOIDS
DISPERSIONS
EARTH ATMOSPHERE
PHOTOCHEMICAL REACTIONS
RADIATIONS
SOLS
STELLAR RADIATION
SYNTHESIS
500200* - Environment
Atmospheric- Chemicals Monitoring & Transport- (-1989)