dissolved and particulate river fluxes of three of the
major bioessential elements found in organic matter,
C, N, and P (the other three are S, hydrogen (H), and
oxygen (O)). Although these elements are considered
minor constituents of river water, their fluxes may
have doubled over their pristine values on a global
scale because of human activities. Excessive riverborne nutrients and the cultural eutrophication of
freshwater and coastal marine ecosystems go hand in
hand. In turn, these fluxes have become sensitive
indicators of the broader global change issues of
population growth and land-use change (including
water resources engineering works) in the coastal
zone and upland drainage basins, climatic change,
and sea level rise.
In contrast to the situation for the major elements,
delivery of some trace elements from land to
the oceans via the atmosphere can rival riverine inputs. The strength of the atmospheric sources
strongly depends on geography and meteorology.
Hence the North Atlantic, western North Pacific,
and Indian Oceans, and their inland seas, are subjected to large atmospheric inputs because of their
proximity to both deserts and industrial sources.
Crustal dust is the primary terrestrial source of these
atmospheric inputs to the ocean. Because of the low
solubility of dust in both atmospheric precipitation
and seawater and the overwhelming inputs from
river sources, dissolved sources of the elements are
generally less important. However, because the
oceans contain only trace amounts of iron (Fe),
aluminum (Al), and manganese (Mn) (concentrations
are in the ppb level), even the small amount of dissolution in seawater (B10% of the element in the
solid phase) results in eolian dust being the primary
source for the dissolved transport of these elements
toremote areas of the ocean. Atmospheric transport
of the major nutrients N, silicon (Si), and Fe to the
ocean has been hypothesized to affect and perhaps
limit primary productivity in certain regions of the
ocean at certain times. Modern processes of fossil
fuel combustion and biomass burning have significantly modified the atmospheric transport from land
to the ocean of trace metals like Pb, copper (Cu), and
zinc (Zn), C in elemental and organic forms, and
nutrient N.
As an example of global land–sea transfers involving gases and the effect of human activities on
the exchange, consider the behavior of CO 2 gas.
Prior to human influence on the system, there was a
net flux of CO 2 out of the ocean owing to organic
metabolism (net heterotrophy). This flux was mainly
supported by the decay of organic matter produced
by phytoplankton in the oceans and part of that
transported by rivers to the oceans. An example
overall reaction is:
C 106 H 263 O 110 N 16 S 2 P þ 141O 2 ) 106CO 2
þ 6HNO 3 þ 2H 2 SO 4 þ H 3 PO 4 þ 120H 2 O
½1
Carbon dioxide was also released to the atmosphere
due to the precipitation of carbonate minerals in the
oceans. The reaction is:
Ca
2þ þ 2HCO
À
3 ) CaCO 3 þ CO 2 þH 2 O ½2
The CO 2 in both reactions initially entered the dissolved inorganic carbon (DIC) pool of seawater and
was subsequently released to the atmosphere at an
annual rate of about 0.2 Â 10
9 t of carbon as CO 2
gas. It should be recognized that this is a small
number compared with the 200 Â 10
9 t of carbon
that exchanges between the ocean and atmosphere
each year because of primary production of organic
matter and its subsequent respiration.
Despite the maintenance of the net heterotrophic
status of the ocean and the continued release of CO 2
to the ocean–atmosphere owing to the formation of
calcium carbonate in the ocean, the modern ocean
and the atmosphere have become net sinks of anthropogenic CO 2 from the burning of fossil fuels and
the practice of deforestation. Over the past 200
years, as CO 2 has accumulated in the atmosphere,
the gradient of CO 2 concentration across the atmosphere–ocean interface has changed, favoring
uptake of anthropogenic CO 2 into the ocean. The
average oceanic carbon uptake for the decade of
the 1990s was c. 2 Â 10
9 t annually. The waters
of the ocean have accumulated about 130 Â 10
9 t of
anthropogenic CO 2 over the past 300 years.
The Coastal Zone and Land–Sea
Exchange Fluxes
The global coastal zone environment is an important
depositional and recycling site for terrigenous and
oceanic biogenic materials. The past three centuries
have been the time of well-documented human activities that have become an important geological
factor affecting the continental and oceanic surface
environment. In particular, historical increases in the
global population in the areas of the major river
drainage basins and close to oceanic coastlines have
been responsible for increasing changes in land-use
practices and discharges of various substances into
oceanic coastal waters. As a consequence, the global
C cycle and the cycles of N and P that closely interact
with the carbon cycle have been greatly affected.
Several major perturbations of the past three
LAND–SEA GLOBAL TRANSFERS 487
major bioessential elements found in organic matter,
C, N, and P (the other three are S, hydrogen (H), and
oxygen (O)). Although these elements are considered
minor constituents of river water, their fluxes may
have doubled over their pristine values on a global
scale because of human activities. Excessive riverborne nutrients and the cultural eutrophication of
freshwater and coastal marine ecosystems go hand in
hand. In turn, these fluxes have become sensitive
indicators of the broader global change issues of
population growth and land-use change (including
water resources engineering works) in the coastal
zone and upland drainage basins, climatic change,
and sea level rise.
In contrast to the situation for the major elements,
delivery of some trace elements from land to
the oceans via the atmosphere can rival riverine inputs. The strength of the atmospheric sources
strongly depends on geography and meteorology.
Hence the North Atlantic, western North Pacific,
and Indian Oceans, and their inland seas, are subjected to large atmospheric inputs because of their
proximity to both deserts and industrial sources.
Crustal dust is the primary terrestrial source of these
atmospheric inputs to the ocean. Because of the low
solubility of dust in both atmospheric precipitation
and seawater and the overwhelming inputs from
river sources, dissolved sources of the elements are
generally less important. However, because the
oceans contain only trace amounts of iron (Fe),
aluminum (Al), and manganese (Mn) (concentrations
are in the ppb level), even the small amount of dissolution in seawater (B10% of the element in the
solid phase) results in eolian dust being the primary
source for the dissolved transport of these elements
toremote areas of the ocean. Atmospheric transport
of the major nutrients N, silicon (Si), and Fe to the
ocean has been hypothesized to affect and perhaps
limit primary productivity in certain regions of the
ocean at certain times. Modern processes of fossil
fuel combustion and biomass burning have significantly modified the atmospheric transport from land
to the ocean of trace metals like Pb, copper (Cu), and
zinc (Zn), C in elemental and organic forms, and
nutrient N.
As an example of global land–sea transfers involving gases and the effect of human activities on
the exchange, consider the behavior of CO 2 gas.
Prior to human influence on the system, there was a
net flux of CO 2 out of the ocean owing to organic
metabolism (net heterotrophy). This flux was mainly
supported by the decay of organic matter produced
by phytoplankton in the oceans and part of that
transported by rivers to the oceans. An example
overall reaction is:
C 106 H 263 O 110 N 16 S 2 P þ 141O 2 ) 106CO 2
þ 6HNO 3 þ 2H 2 SO 4 þ H 3 PO 4 þ 120H 2 O
½1
Carbon dioxide was also released to the atmosphere
due to the precipitation of carbonate minerals in the
oceans. The reaction is:
Ca
2þ þ 2HCO
À
3 ) CaCO 3 þ CO 2 þH 2 O ½2
The CO 2 in both reactions initially entered the dissolved inorganic carbon (DIC) pool of seawater and
was subsequently released to the atmosphere at an
annual rate of about 0.2 Â 10
9 t of carbon as CO 2
gas. It should be recognized that this is a small
number compared with the 200 Â 10
9 t of carbon
that exchanges between the ocean and atmosphere
each year because of primary production of organic
matter and its subsequent respiration.
Despite the maintenance of the net heterotrophic
status of the ocean and the continued release of CO 2
to the ocean–atmosphere owing to the formation of
calcium carbonate in the ocean, the modern ocean
and the atmosphere have become net sinks of anthropogenic CO 2 from the burning of fossil fuels and
the practice of deforestation. Over the past 200
years, as CO 2 has accumulated in the atmosphere,
the gradient of CO 2 concentration across the atmosphere–ocean interface has changed, favoring
uptake of anthropogenic CO 2 into the ocean. The
average oceanic carbon uptake for the decade of
the 1990s was c. 2 Â 10
9 t annually. The waters
of the ocean have accumulated about 130 Â 10
9 t of
anthropogenic CO 2 over the past 300 years.
The Coastal Zone and Land–Sea
Exchange Fluxes
The global coastal zone environment is an important
depositional and recycling site for terrigenous and
oceanic biogenic materials. The past three centuries
have been the time of well-documented human activities that have become an important geological
factor affecting the continental and oceanic surface
environment. In particular, historical increases in the
global population in the areas of the major river
drainage basins and close to oceanic coastlines have
been responsible for increasing changes in land-use
practices and discharges of various substances into
oceanic coastal waters. As a consequence, the global
C cycle and the cycles of N and P that closely interact
with the carbon cycle have been greatly affected.
Several major perturbations of the past three
LAND–SEA GLOBAL TRANSFERS 487