CFCS IN THE OCEAN
R. A. Fine, University of Miami, Miami, FL, USA
Copyright & 2001 Elsevier Ltd.
Introduction
The oceans, atmosphere, continents, and cryosphere
are part of the tightly connected climate system.
The ocean’s role in the climate system involves the
transport, sequestration, and exchange of heat,
fresh water, and carbon dioxide (CO 2 ) between the
other components of the climate system. When
waters descend below the ocean surface they carry
with them atmospheric constituents. Some of these
are gases such as carbon dioxide and chlorofluorocarbons (CFCs). The CFCs can serve as a physical
analog for CO 2 because they are biologically and
chemically inert in oceans. In the oceans the distribution of CFCs provides information on which
waters have been in contact with the atmosphere in
the past few decades. The CFCs also give information on the ocean’s circulation and its variability
on timescales of months to decades. The timescale
information is needed to understand and to assess
the ocean’s role in climate change, and its capacity
to take up anthropogenic constituents from the atmosphere. Thus, the advantage of using tracers like
CFCs for ocean circulation studies is the added dimension of time; their time history is fairly well
known, they are an integrating quantity and an
analog for oceanic anthropogenic CO 2 uptake, and
they provide an independent test for time integration of models.
Tracers serve as a ‘dye’ with which to follow the
circulation of ocean waters. There are conventional ocean tracers such as temperature, salinity,
oxygen, and nutrients. There are stable isotope
tracers such as oxygen-18, carbon-13, and there are
radioactive tracers both naturally occurring (such
as the uranium/thorium series, and radium), and
those produced both naturally and by the bomb
tests (such as tritium and carbon-14). The bomb
contributions from the latter two are called transient tracers, as are the CFCs, because they have
been in the atmosphere for a short time. This implies an anthropogenic source and a nonsteady
input function.
Atmospheric Source
The chlorofluorocarbons, CFCs, are synthetic halogenated methanes. Their chemical structures are as
follows: CFC-11 is CCl 3 F, CFC-12 is CCl 2 F 2 , and
CFC-113 is CCl 2 FCClF 2 . For completeness the
compound carbon tetrachloride, CCl 4 , is also included in this article as its atmospheric source,
measurement, and oceanic distribution are similar to
those of the CFCs. The CFCs have received considerable attention because they are a double-edged
environmental sword. They are a threat to the ozone
layer, and a greenhouse gas. The CFCs are used as
coolants in refrigerators and air conditioners, as
propellants in aerosol spray cans, and as foaming
agents. These chemicals were developed over 50
years ago when no one realized that they might cause
environmental problems. When released CFCs are
gases that have two sinks, the predominant one being
the atmosphere, and to a lesser extent the oceans.
Most of the CFCs go up into the troposphere, where
they remain for decades. In the oceans and in the
troposphere the CFCs pose no problem. However,
some escape into the stratosphere where they are a
threat to the ozone layer. Due to their role in UV
absorption they have been correlated with the increased incidence of skin cancers. Since the recognition of the CFCs as an environmental problem in
the 1970s and the signing of the Montreal Protocol
in 1987, the use of CFCs has been phased out. The
atmospheric concentrations have just started to decrease. This is an important international step
toward correcting the dangerous trend of stratospheric ozone depletion.
The atmospheric CFC concentrations became significant after the 1940s. The concentrations increased exponentially until the mid-1970s, and then
increased linearly until the 1990s at a rate of about
5% per year. The production and release data for
CFCs tabulated by the Chemical Manufacturers Association (CMA) were used (Figure 1) to reconstruct
the atmospheric time histories for the Northern and
Southern Hemispheres. Since 1979 the atmospheric
concentrations have been based on actual measurements at various sampling stations around the globe,
and these are checked against the CMA production
and release estimates. The curves in Figure 1 show all
CFCs including CCl 4 increasing with time, with
CFC-11 leveling off and actually decreasing in the
late 1990s. The atmospheric increase of all the CFCs
slowed markedly after the Montreal Protocol. The
155
R. A. Fine, University of Miami, Miami, FL, USA
Copyright & 2001 Elsevier Ltd.
Introduction
The oceans, atmosphere, continents, and cryosphere
are part of the tightly connected climate system.
The ocean’s role in the climate system involves the
transport, sequestration, and exchange of heat,
fresh water, and carbon dioxide (CO 2 ) between the
other components of the climate system. When
waters descend below the ocean surface they carry
with them atmospheric constituents. Some of these
are gases such as carbon dioxide and chlorofluorocarbons (CFCs). The CFCs can serve as a physical
analog for CO 2 because they are biologically and
chemically inert in oceans. In the oceans the distribution of CFCs provides information on which
waters have been in contact with the atmosphere in
the past few decades. The CFCs also give information on the ocean’s circulation and its variability
on timescales of months to decades. The timescale
information is needed to understand and to assess
the ocean’s role in climate change, and its capacity
to take up anthropogenic constituents from the atmosphere. Thus, the advantage of using tracers like
CFCs for ocean circulation studies is the added dimension of time; their time history is fairly well
known, they are an integrating quantity and an
analog for oceanic anthropogenic CO 2 uptake, and
they provide an independent test for time integration of models.
Tracers serve as a ‘dye’ with which to follow the
circulation of ocean waters. There are conventional ocean tracers such as temperature, salinity,
oxygen, and nutrients. There are stable isotope
tracers such as oxygen-18, carbon-13, and there are
radioactive tracers both naturally occurring (such
as the uranium/thorium series, and radium), and
those produced both naturally and by the bomb
tests (such as tritium and carbon-14). The bomb
contributions from the latter two are called transient tracers, as are the CFCs, because they have
been in the atmosphere for a short time. This implies an anthropogenic source and a nonsteady
input function.
Atmospheric Source
The chlorofluorocarbons, CFCs, are synthetic halogenated methanes. Their chemical structures are as
follows: CFC-11 is CCl 3 F, CFC-12 is CCl 2 F 2 , and
CFC-113 is CCl 2 FCClF 2 . For completeness the
compound carbon tetrachloride, CCl 4 , is also included in this article as its atmospheric source,
measurement, and oceanic distribution are similar to
those of the CFCs. The CFCs have received considerable attention because they are a double-edged
environmental sword. They are a threat to the ozone
layer, and a greenhouse gas. The CFCs are used as
coolants in refrigerators and air conditioners, as
propellants in aerosol spray cans, and as foaming
agents. These chemicals were developed over 50
years ago when no one realized that they might cause
environmental problems. When released CFCs are
gases that have two sinks, the predominant one being
the atmosphere, and to a lesser extent the oceans.
Most of the CFCs go up into the troposphere, where
they remain for decades. In the oceans and in the
troposphere the CFCs pose no problem. However,
some escape into the stratosphere where they are a
threat to the ozone layer. Due to their role in UV
absorption they have been correlated with the increased incidence of skin cancers. Since the recognition of the CFCs as an environmental problem in
the 1970s and the signing of the Montreal Protocol
in 1987, the use of CFCs has been phased out. The
atmospheric concentrations have just started to decrease. This is an important international step
toward correcting the dangerous trend of stratospheric ozone depletion.
The atmospheric CFC concentrations became significant after the 1940s. The concentrations increased exponentially until the mid-1970s, and then
increased linearly until the 1990s at a rate of about
5% per year. The production and release data for
CFCs tabulated by the Chemical Manufacturers Association (CMA) were used (Figure 1) to reconstruct
the atmospheric time histories for the Northern and
Southern Hemispheres. Since 1979 the atmospheric
concentrations have been based on actual measurements at various sampling stations around the globe,
and these are checked against the CMA production
and release estimates. The curves in Figure 1 show all
CFCs including CCl 4 increasing with time, with
CFC-11 leveling off and actually decreasing in the
late 1990s. The atmospheric increase of all the CFCs
slowed markedly after the Montreal Protocol. The
155