Ozone perturbation from medium-size asteroid impacts in the ocean Authors: E. Pierazzo, R.R. Garcia, D.E. Kinnison, D.R. Marsh, J. Lee-Taylor, P.J. Crutzen Viktoriya Stoeva and Sara Cohen
Introduction • Evidence was presented which investigates the effects of possible oceanic impacts of 500 m and 1 km diameter asteroids on Earth’s atmosphere • Large impacts from these asteroids can lead to ozone depletion which may cause damaging effects due to an increase of Ultraviolet (UV) radiation at Earth’s surface. Impacts may lead to a disturbance of the chemical composition of the atmosphere which is life threatening to living organisms inhabiting Earth’s surface.
Near-Earth Objects • Currently over 817 Near-Earth Objects (NEOs) have been found larger than 1 kilometer (km) in diameter in close proximity to Earth. • Objects over 1 km in diameter are capable of causing destruction leading to a global climate disaster and demolishing human civilization.
Water on the Earth’s Surface • Over 70% of Earth’s surface is covered by water. • Two thirds is covered by oceans over 1 km deep.
Impact Plume • A water impact would eject water in the form of a vapor and liquid. For an object with a mass of 1 km, the impact would extend over 1,000 km into the atmosphere. The impact plume will then collapse back towards Earth’s atmosphere. This will cause large waves leading to hazardous tsunamis at the origin of the impact on Earth’s surface.
Time and Location • The time and location of the impact will determine the effects of the overall perturbation of the atmosphere. • Impacts at high latitudes in the Northern hemisphere cause atmospheric disturbances that may stay confined to the hemisphere the impact is located in; whereas atmospheric perturbations from tropical impacts have a greater possibility to spread to both hemispheres.
Chemicals of the Impact • The liquid water from a plume will precipitate and will not further affect the chemistry of the atmosphere. • Other gasses produced in the impact also have an effect on Earth’s atmosphere. • Halogens from sea salt contained in vaporized sea water and NO can produce significant ozone depletion in the stratosphere. • As the halogens and NO spread globally, the ozone depletion values can become greater than 70% for more than 2 years.
Ozone Depletion • UV radiation absorbed by the ozone is the main source of heat in the upper atmosphere and provides a natural sunblock to UV radiation reaching the Earth’s surface. • Ozone depletion will lead to significant cooling in the upper atmosphere, however it will not extend to the lower atmosphere. • The removal of significant amounts of ozone in the upper atmosphere will put life on Earth in danger.
UV Irradiance • UV irradiance can cause sunburns which are rated on a scale of a constant value to produce values on a nominal scale. • UVI values greater than ten are considered to be extreme and will severely burn unprotected skin in only minutes. • If an asteroid with a diameter of 1 km impacted water these values would exceed twenty for the first two years following the impact.
Plant Life • Plants account for most of the living mass in terrestrial ecosystems. • Plants have a dependence on sunlight for survival and an inability to move. These factors cause higher plants in particular to be susceptible to increases in UV-B irradiance. • Some effects may be decrease in plant height, decreased shoot mass, and a loss of foliage area.
Harmful Effects to Plant Life • Although plants may respond well to increases in UV-B radiation, during periods of prolonged exposure not all DNA damage may be repaired. • Damage can accumulate over time and carry over to succeeding plant generations, affecting each plants genetic stability due to the increase in frequency of mutations. • Indirect effects of increased UV-B exposure may decrease the productivity of agricultural regions worldwide and have remarkable consequences on human sustainability.
Aquaculture • Over 30% of animal protein consumed by humans comes from sea life, typically in the form of finfish, shellfish, and seaweed. • Higher UV-B levels caused by ozone depletion hinder phytoplankton activity in the ocean. • Predictions show that an estimated 16% ozone depletion would have an end result of a 5% decrease in phytoplankton. This could directly reduce fishery and yield aquaculture by nearly 7%. The result would also uphold a loss of about seven million tons of fish per year.
UV-B fluxes • Impacts from NEOs with a diameter of 1 km may create ecological changes in time as a result of enhanced UV-B fluxes at Earth’s surface.
Conclusion • Oceanic impacts from asteroids 1 km in diameter may cause a notable perturbation of the atmospheric chemical composition. • Several years of ozone depletion will occur on a global scale as a result of an impact of a medium (1 km) sized asteroid. • UV-B irradiance resulting from an impact can be hazardous for living organisms on Earth. • A medium sized impact would have a direct long lasting effect on global food production, which would have a negative effect on the sustainability of the human population. • Although an impact in water would not immediately lead to extinction, there would still be a dramatic effect on all living organisms.
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