Download What is ozone?

Ozone Depletion:
Its Adverse Effects Upon Marine Life
“Human-induced global climate change also threatens marine biodiversity. There is little doubt
that global warming is taking place as a result of the accumulation of carbon dioxide, methane,
and other greenhouse gases. The breakdown of stratospheric ozone due to continued
accumulation in the upper atmosphere of certain widely used volatile chemicals, especially the
chlorofluorocarbons (CFCs) used as refrigerants, cleaning solvents, and aerosol propellants,
also threatens marine organisms living near the surface of the sea.”º¹
What is ozone?
The ozone layer is believed to
have formed nearly 2 billion years
ago as blue-green bacteria evolved
and began producing oxygen (O2).
The creation of ozone was initiated
when photons with wavelengths less
than 240 nanometers collided with O2
molecules in the stratospheric layer of
the atmosphere. This collision caused
the O2 atoms to break apart. The
newly separated odd O2 atoms were
highly reactive and thus combined
with normal O2 molecules to form
ozone (O3). Ozone is blue in color
and tends to have a strong odor.
According to the U.S. Environmental
Protection Agency, “out of each 10
million air molecules, about 2 million
are normal oxygen, but only 3 are
ozone.”º³
The two most important functions
of ozone are the absorption of UV- B
light and a decrease in penetration of
energetic radiation through the
atmosphere.
http://www.epa.gov/ozone/science/sc_fact
As shown in the graph above, variations in the
ozone layer occur at different altitudes in the
atmosphere. Variations also occur above different
latitudes across the globe. Most atmospheric
ozone is concentrated in a single layer throughout
the stratosphere. Tropospheric ozone, also
referred to as ‘photochemical smog’, is transported
downward by weather systems. UV radiation
interacts with nitrogen oxide and other pollutants.²
The diagram to the right graphically
details the natural formation and
destruction of ozone in the
atmosphere. The diagram also
explains how this process contributes
to global warming, a phenomenon
that shares a complex relationship
with ozone depletion.
www.epa.gov/ozone/science/process.html
What agents deplete the ozone layer?
*The ozone depletion process begins when CFCs and other ozone depleting substances (ODS) are emitted into the atmosphere.
www.epa.gov/ozone/science/process.html
Ozone is not a stable
molecule and can be
broken down through
various chemical
reactions which may
involve odd hydrogen
atoms, odd nitrogen
atoms, and/or chlorine
atoms. Various causes
disrupt the balance
between natural
creative and destructive
forces upon the ozone
layer. These include but
are not limited to natural
meteorological
phenomena, volcanic
eruptions, and manmade chemicals.
NATURAL METEOROLOGICAL PHENOMENA
Nitrogen oxides play a significant
role in the natural destruction of the
ozone layer. However, when only this
substance is involved in natural
destruction, a balance exists between
creative and destructive forces. “At
any given time, ozone molecules are
constantly formed and destroyed in the
stratosphere. The total amount,
however, remains relatively stable.”º³
This means that the reduction in ozone
levels is always counteracted by a
recovery and reformation of ozone.
Evidential research reveals that the
ozone layer is being depleted far
beyond changes due to such natural
processes. º³
VOLCANIC ERUPTIONS
Large volcanic eruptions indirectly
affect atmospheric ozone levels.
Volcanoes such as Mount Pinatubo in
the Philippines emit sulfur dioxide upon
eruption. This gas is quickly converted
into sulfuric acid aerosols which catalyze
the destructive chemical reactions
naturally occurring in the ozone layer.
Significant to note is that the destructive
effects of the aerosols produced from
sulfur dioxide only last about two years.
Man-made chlorine compounds on the
other hand can have effects upon ozone
depletion for 100 years or more.²
MAN-MADE CHEMICALS
Chlorofluorocarbons (CFCs) found in refrigerator coolants, insulating foam, and as
propellants in spray cans are stable, non-flammable, low in toxicity, cheap, and
relatively ‘safe’ products. However, these and other synthetic chemicals such as
HCFCs and bromine compounds used in fire-fighting account for nearly 84% of
chlorine in the stratosphere while natural sources contribute only about 16% of total
stratospheric chlorine. As demonstrated in the illustration above, once chlorine
atoms are released from these compounds, they significantly damage the protective
ozone layer. With large depletions of ozone, levels of UV-B radiation reaching
Earth’s surface increase exponentially. º³
How does ozone depletion affect marine life?
PHYTOPLANKTON
Not only does UV-B light
damage from ozone
depletion decrease the suncatching capacity of
phytoplankton, but also the
decrease in ozone allows
light of shorter, more
energy-rich wavelengths to
reach Earth’s surface and
have more devastating
effects upon even the
smallest of marine species.
“Ultraviolet radiation injures
living things by breaking
strands of DNA and
unfolding protein molecules.
Species normally exposed
to sunlight have evolved
defenses against aver
amounts of ultraviolet
radiation, but increased
amounts could overwhelm
those defenses.Ӽ This
damage to genetic material
affects survival of the cell.
UV radiation also bleaches
the sun-catching pigments,
affects photosynthetic
machinery that allows
phytoplankton to catch light
energy and transfer it to
chemical bonds, and also
impairs the ability to utilize
nitrogen for metabolic
processes.² In research
focused on aquatic
ecosystems, “one
experiment of enhanced UV
in estuarine
microecosystems found
large losses in productivity,
biomass, and diversity.³
Source: ²
As demonstrated in the illustration above, a decrease in
the phytoplankton population due to increased UV radiation
from ozone depletion would also impact animals higher up
in the food chain because species are interdependent upon
one another for food resources.
SENSITIVE FROG EGGS
While increased UV-B radiation has not conclusively
been identified as the sole cause for amphibian population
decline, there are certainly strong correlations. Amphibian
eggs lack a hard, outer shell thus heightening their
sensitivity to UV damage. Frogs eggs are affected more
than other amphibian species because they tend to lay their
eggs in shallow water. Unless frog species have adapted or
can adapt internal protective mechanisms against UV
radiation, their population could be in danger if ozone
depletion continues at current levels.²
EGGS & LARVAE
Since eggs and larvae of many fish and crustaceans
float at the ocean’s surface, they are highly sensitive to UVB radiation. While damage depends on the efficiency of
DNA repair and behavioral responses, even minor
alterations in amounts of UV-B at critical life stages might
be detrimental for some species.²
CYANOBACTERIA
“In cyanobacteria, growth, differentiation, photosynthesis,
and nitrogen incorporation have been found to be affected
by solar UV radiation.”º² Given that cyanobacteria constitute
nearly 40% of marine biomass and are capable of
converting atmospheric nitrogen into a useable form that
can be utilized by phytoplankton and more complex plant
species, their population decline will adversely affect other
marine organisms.º²
A brighter (or better yet a dimmer) future?
The image to the right displays
the latest global distribution of
ozone. Various trends in
depletion exist as it significantly
varies both geographically and
depending on the season. “Over
the populated mid-latitudes (3060°), the average rate of
depletion is 4-5 percent per
decade…Over the Arctic, the
cumulative ozone depletion is
about 20 percent, while there are
no significant trends in the
tropics.”² Ozone depletion can be
seen at its worst over Antarctica.
Every winter, a polar vortex
isolates much of the Antarctic
stratosphere. Since there is no
sun, the air becomes extremely
cold and stimulates the growth of
ice clouds. Ice crystals within the
clouds provide for the conversion
of chlorine into an active form
upon the return of light in the
spring. This extreme climate
primes the stratosphere for
destruction.¹
www.albany.edu/faculty/rgk/atm101/ozone
What can we do?
•
•
•
•
•
uphold the 1987 Montreal Protocol
• completely phase out CFCs
• regulate substances containing chlorine &
bromine
end production of CFCs and halons
encourage companies to convert to “ozonefriendly” technologies
eliminate smuggling of CFCs
actively participate in programs under Title VI of
the clean air act:
• refrigerant recycling
(end practice of venting refrigerants into the air)
• product labeling
(those either containing or made with ozonedepleting substances)
•banning nonessential uses of certain
compounds (i.e. CFCs & HCFCs)
• reviewing substitutes
(for ozone-depleting substances)
“Marine biodiversity is threatened just as terrestrial biodiversity is
threatened. Human excesses—the overwhelming growth of populations and the
unchecked wastefulness of “advanced” societies—are causing environmental
disturbances that cascade from land to sea at a perilous rate. Life in the sea is
vulnerable to the environmental consequences of the way we live.”º¹ We must be
ever aware of our impact upon the environment, in this case depletion of the
ozone layer, and how it is destroying the most amazing creatures on our
planet…those in the sea.
Sources
ºGarrison, Tom. Essentials of Oceanography. United States: Thomson Learning, Inc.,
2006.
¹Hoffman, Matthew J. Ozone Depletion and Climate Change: Constructing a Global
Response. Albany, New York: State University of New York Press, 2005.
²Nilsson, Annika. Ultraviolet Reflections: Life Under a Thinning Ozone Layer. New
York: John Wiley & Sons Ltd., 1996.
³Parson, Edward A. Protecting the Ozone Layer. New York: Oxford University Press,
Inc., 2003.
º¹Thorne-Miller. The Living Ocean: Understanding and Protecting Marine Biodiversity.
2nd ed. Washington, DC: Island Press, 1999.
º²United Nations Environment Programme. Environmental Effects of Ozone Depletion.
Sept. 1999. 7 March 2007 <http://www.gcrio.org/ozone/unep1999summary.html>
º³United States Environmental Protection Agency. Ozone Depletion: The Facts Behind
the Phaseout. March 1994. 7 March 2007 <http://www.epa.gov/ttn/oarpg/
t6/reports/862.txt>.