centuries of the industrial age have affected the
processes of transport from land, deposition of terrigenous materials, and in situ production of organic
matter in coastal zone environments. In addition,
potential future changes in oceanic circulation may
have significant effects on the biogeochemistry and
CO 2 exchange in the coastal zone.
The coastal zone is that environment of continental shelves, including bays, lagoons, estuaries,
and near-shore banks that occupy 7% of the surface
area of the ocean (36 Â 10
12 m
2
) or c. 9% of the
volume of the surface mixed layer of the ocean
(3 Â 10
15 m
3 ). The continental shelves average 75 km
in width, with a bottom slope of 1.7 m km
À 1 . They
are generally viewed as divisible into the interior or
proximal shelf, and the exterior or distal shelf.
The mean depth of the global continental shelf is
usually taken as the depth of the break between the
continental shelf and slope at c. 200 m, although this
depth varies considerably throughout the world’s
oceans. In the Atlantic, the median depth of the
shelf-slope break is at 120 m, with a range from
80 to 180 m. The depths of the continental shelf
are near 200 m in the European section of the
Atlantic, but they are close to 100 m on the African
and North American coasts. Coastal zone environments that have high sedimentation rates, as great as
30–60 cm ky
–1 in active depositional areas, act as
traps and filters of natural and human-generated
materials transported from continents to the oceans
via river and groundwater flows and through the
atmosphere. At present a large fraction (B80%) of
the land-derived organic and inorganic materials that
are transported to the oceans is trapped on the
proximal continental shelves. The coastal zone also
accounts for 30–50% of total carbonate and 80% of
organic carbon accumulation in the ocean. Coastal
zone environments are also regions of higher biological production relative to that of average oceanic
surface waters, making them an important factor in
the global carbon cycle. The higher primary production is variably attributable to the nutrient inflows from land as well as from coastal upwelling of
deeper ocean waters.
Fluvial and atmospheric transport links the coastal
zone to the land; gas exchange and deposition are its
links with the atmosphere; net advective transport of
water, dissolved solids and particles, and coastal
upwelling connect it with the open ocean. In addition, coastal marine sediments are repositories for
much of the material delivered to the coastal zone. In
the last several centuries, human activities on land
have become a geologically important agent affecting
the land–sea exchange of materials. In particular,
river and groundwater flows and atmospheric
transport of materials to the coastal zone have been
substantially altered.
Bioessential Elements
Continuous increase in the global population and its
industrial and agricultural activities have created
four major perturbations on the coupled system of
the biogeochemical cycles of the bioessential elements C, N, P, and S. These changes have led to
major alterations in the exchanges of these elements
between the land and sea. The perturbations are:
(1) emissions of C, N, and S to the atmosphere from
fossil-fuel burning and subsequent partitioning of
anthropogenic C and deposition of N and S;
(2) changes in land-use practices that affect the recycling of C, N, P, and S on land, their uptake by
plants and release from decaying organic matter, and
the rates of land surface denudation; (3) additions of N
and P in chemical fertilizers to cultivated land area;
and (4) releases of organic wastes containing highly
reactive C, N, and P that ultimately enter the coastal
zone. A fifth major perturbation is a climatic one: (5)
the rise in mean global temperature of the lower atmosphere of about 1 1C in the past 300 years, with a
projected increase of about 1.4–5.8 1C relative to 1990
by the year 2100. Figure 1 shows how the fluxes associated with these activities have changed during the
past three centuries with projections to the year 2040.
Partially as a result of these activities on land, the
fluxes of materials to the coastal zone have changed
historically. Figure 2 shows the historical and projected future changes in the river fluxes of dissolved
inorganic and organic carbon (DIC, DOC), nitrogen
(DIN, DON), and phosphorus (DIP, DOP), and
fluxes associated with the atmospheric deposition
and denitrification of N, and accumulation of C in
organic matter in coastal marine sediments. It can be
seen in Figure 2 that the riverine fluxes of C, N, and P
all increase in the dissolved inorganic and organic
phases from about 1850 projected to 2040. For example, for carbon, the total flux (organic þ inorganic) increases by about 35% during this period.
These increased fluxes are mainly due to changes in
land-use practices, including deforestation, conversion of forest to grassland, pastureland, and
urban centers, and regrowth of forests, and application of fertilizers to croplands and the subsequent
leaching of N and P into aquatic systems.
Inputs of nutrient N and P to the coastal zone
which support new primary production are from the
land by riverine and groundwater flows, from the
open ocean by coastal upwelling and onwelling, and
to a lesser extent by atmospheric deposition of nitrogen. New primary production depends on the
488 LAND–SEA GLOBAL TRANSFERS
processes of transport from land, deposition of terrigenous materials, and in situ production of organic
matter in coastal zone environments. In addition,
potential future changes in oceanic circulation may
have significant effects on the biogeochemistry and
CO 2 exchange in the coastal zone.
The coastal zone is that environment of continental shelves, including bays, lagoons, estuaries,
and near-shore banks that occupy 7% of the surface
area of the ocean (36 Â 10
12 m
2
) or c. 9% of the
volume of the surface mixed layer of the ocean
(3 Â 10
15 m
3 ). The continental shelves average 75 km
in width, with a bottom slope of 1.7 m km
À 1 . They
are generally viewed as divisible into the interior or
proximal shelf, and the exterior or distal shelf.
The mean depth of the global continental shelf is
usually taken as the depth of the break between the
continental shelf and slope at c. 200 m, although this
depth varies considerably throughout the world’s
oceans. In the Atlantic, the median depth of the
shelf-slope break is at 120 m, with a range from
80 to 180 m. The depths of the continental shelf
are near 200 m in the European section of the
Atlantic, but they are close to 100 m on the African
and North American coasts. Coastal zone environments that have high sedimentation rates, as great as
30–60 cm ky
–1 in active depositional areas, act as
traps and filters of natural and human-generated
materials transported from continents to the oceans
via river and groundwater flows and through the
atmosphere. At present a large fraction (B80%) of
the land-derived organic and inorganic materials that
are transported to the oceans is trapped on the
proximal continental shelves. The coastal zone also
accounts for 30–50% of total carbonate and 80% of
organic carbon accumulation in the ocean. Coastal
zone environments are also regions of higher biological production relative to that of average oceanic
surface waters, making them an important factor in
the global carbon cycle. The higher primary production is variably attributable to the nutrient inflows from land as well as from coastal upwelling of
deeper ocean waters.
Fluvial and atmospheric transport links the coastal
zone to the land; gas exchange and deposition are its
links with the atmosphere; net advective transport of
water, dissolved solids and particles, and coastal
upwelling connect it with the open ocean. In addition, coastal marine sediments are repositories for
much of the material delivered to the coastal zone. In
the last several centuries, human activities on land
have become a geologically important agent affecting
the land–sea exchange of materials. In particular,
river and groundwater flows and atmospheric
transport of materials to the coastal zone have been
substantially altered.
Bioessential Elements
Continuous increase in the global population and its
industrial and agricultural activities have created
four major perturbations on the coupled system of
the biogeochemical cycles of the bioessential elements C, N, P, and S. These changes have led to
major alterations in the exchanges of these elements
between the land and sea. The perturbations are:
(1) emissions of C, N, and S to the atmosphere from
fossil-fuel burning and subsequent partitioning of
anthropogenic C and deposition of N and S;
(2) changes in land-use practices that affect the recycling of C, N, P, and S on land, their uptake by
plants and release from decaying organic matter, and
the rates of land surface denudation; (3) additions of N
and P in chemical fertilizers to cultivated land area;
and (4) releases of organic wastes containing highly
reactive C, N, and P that ultimately enter the coastal
zone. A fifth major perturbation is a climatic one: (5)
the rise in mean global temperature of the lower atmosphere of about 1 1C in the past 300 years, with a
projected increase of about 1.4–5.8 1C relative to 1990
by the year 2100. Figure 1 shows how the fluxes associated with these activities have changed during the
past three centuries with projections to the year 2040.
Partially as a result of these activities on land, the
fluxes of materials to the coastal zone have changed
historically. Figure 2 shows the historical and projected future changes in the river fluxes of dissolved
inorganic and organic carbon (DIC, DOC), nitrogen
(DIN, DON), and phosphorus (DIP, DOP), and
fluxes associated with the atmospheric deposition
and denitrification of N, and accumulation of C in
organic matter in coastal marine sediments. It can be
seen in Figure 2 that the riverine fluxes of C, N, and P
all increase in the dissolved inorganic and organic
phases from about 1850 projected to 2040. For example, for carbon, the total flux (organic þ inorganic) increases by about 35% during this period.
These increased fluxes are mainly due to changes in
land-use practices, including deforestation, conversion of forest to grassland, pastureland, and
urban centers, and regrowth of forests, and application of fertilizers to croplands and the subsequent
leaching of N and P into aquatic systems.
Inputs of nutrient N and P to the coastal zone
which support new primary production are from the
land by riverine and groundwater flows, from the
open ocean by coastal upwelling and onwelling, and
to a lesser extent by atmospheric deposition of nitrogen. New primary production depends on the
488 LAND–SEA GLOBAL TRANSFERS