Cold seeps
Besides the transport of dissolved substances by rivers and
through the atmosphere, an important transport of
dissolved components and gases takes place on vents
and seeps, as well as diffusive transport between the seafloor and water column. This also includes submarine
releases of groundwater. Seeps are characterized by a special community of benthic organisms, the formation of
massive authigenic carbonates, gas releases, and occurrence of gas hydrates. Chemosynthetic communities are
common, dominated by giant tube worms and large bacterial mats (see “Cold Seeps”).
The return of materials from the sediments into the
water is not limited to the microbiological and diagenetic
processes in the uppermost sediment layers. Similar to
the hydrothermal (“hot”) vents at the mid-oceanic ridges,
recent discoveries of cold seeps along the ocean margins
have revealed ascending fluids flowing into the seawater,
in part originating at great depths in the sediments. These
fluids, often enriched in methane, sporadically maintain
self-sufficient ecosystems based on chemosynthesis such
as those known from the hydrothermal vents.
Recently discovered numerous large carbonate mounds
(see “Carbonate Factories”) located on the continental
slope are associated with the discharge openings of such
fluids. These carbonate deposits are often occupied by a
fascinating ecosystem.
Biology
At ocean margins a large variety of habitats and biological
communities are present, e.g., coral mounds, sediment
slopes and gravel banks, canyons, and mud volcanoes.
With new technology, especially using remotely operated
vehicles (ROVs), new habitats have been discovered in
recent decades. One example is illustrated by deepwater
corals providing a habitat for a great number of other
organisms. These communities are in danger as a result
of increased commercial use of living and nonliving
deepwater resources on the ocean margins, particularly
deep-sea fishing and oil and gas production. Recently discussions have begun regarding the exploration of metals
from the deep sea. This planned exploration must be combined with careful monitoring of the deep-sea environment.
Cold-water corals
Over the past several decades, reef-forming cold-water
corals have been intensively studied (see “Reefs
(Biogenic)”). They are comparable in extent and diversity
to tropical coral reefs. Together with the two dominant
species, Lophelia pertusa and Madrepora oculata, more
than 1,000 other species were identified living in the
cold-water coral environments (Freiwald and Roberts,
2005). Ocean margins contain a large number of different
habitats and biological environments. Because ocean margins are increasingly being used for fisheries, as a biological resource, and for the exploitation of oil, gas, and
minerals, management of the environment and
establishment of conservation areas are under discussion
(e.g., coral reefs off Norway).
Deep biosphere
In addition to these previously unknown ecosystems, significantly more important systems, quantitatively, have
been discovered within the depths of the sediments (see
“Deep Biosphere”). The presence of a rich bacterial life
below the seafloor has been identified, reaching a sediment depth of more than 1,000 m and penetrating even
into the volcanic rocks below the sediment cover. It is estimated that this newly discovered ecosystem accounts for
up to 10 % of the active global biomass.
Human usage
The most obvious impacts of human usage on the oceans
are naturally seen in the coastal regions. As the transition
area between land and sea, the coastal zones are becoming
more and more threatened by increasing intensive use as
residential or industrial areas and as agri- and aquacultural
areas. Added to this are the pressures of harbor sites and
tourism. Already today, 60 % of the world’s population
lives in this zone, and 75 % of all cities with populations
over 2.5 million are located in estuarine regions (see “Integrated Coastal Zone Management”).
In addition to the input of pollutants and nutrients to the
coastal waters, they are increasingly being directly used
for human activities in which clear traces of the use
remain. The shore, banks and shallow-water areas are
being altered by construction (e.g., dikes, harbors, and
pipelines, as well as river-bottom deepening and river correction and gravel and sand removal), which has a lasting
effect on the current conditions, sea-level change
(absolute level and storm-flood frequency), and rates of
erosion and deposition (see “Coastal Engineering” and
“Engineered Coasts”).
On the seaside of the coastal zone, the wide continental
shelf is exploited by fisheries and marine mining (see
“Marine Mineral Resources”). The shelf regions represent
high-productivity regions for fisheries, with 95 % of the
total global catch coming from this zone. They are also
easily accessible for marine mining, especially for the production of oil and gas, as well as gravel and other building
materials. Oil exploration and especially the fisheries have
also begun to advance out onto the continental slope. Fishery activity particularly contributes to large-scale changes
on the seafloor through intensive bottom trawling. This
leads, e.g., to the endangerment of unique ecosystems
such as the cold-water coral reefs that occur on the continental slopes in water depths up to 1,000 m.
Conclusions
Ocean margins are extremely important for mankind due
to their great commercial potential for hydrocarbon exploration and fisheries. On the other hand, these areas possess
a high risk of hazards in the form of earthquakes and
tsunamis. Increasing human activities, including
OCEAN MARGIN SYSTEMS
557
Besides the transport of dissolved substances by rivers and
through the atmosphere, an important transport of
dissolved components and gases takes place on vents
and seeps, as well as diffusive transport between the seafloor and water column. This also includes submarine
releases of groundwater. Seeps are characterized by a special community of benthic organisms, the formation of
massive authigenic carbonates, gas releases, and occurrence of gas hydrates. Chemosynthetic communities are
common, dominated by giant tube worms and large bacterial mats (see “Cold Seeps”).
The return of materials from the sediments into the
water is not limited to the microbiological and diagenetic
processes in the uppermost sediment layers. Similar to
the hydrothermal (“hot”) vents at the mid-oceanic ridges,
recent discoveries of cold seeps along the ocean margins
have revealed ascending fluids flowing into the seawater,
in part originating at great depths in the sediments. These
fluids, often enriched in methane, sporadically maintain
self-sufficient ecosystems based on chemosynthesis such
as those known from the hydrothermal vents.
Recently discovered numerous large carbonate mounds
(see “Carbonate Factories”) located on the continental
slope are associated with the discharge openings of such
fluids. These carbonate deposits are often occupied by a
fascinating ecosystem.
Biology
At ocean margins a large variety of habitats and biological
communities are present, e.g., coral mounds, sediment
slopes and gravel banks, canyons, and mud volcanoes.
With new technology, especially using remotely operated
vehicles (ROVs), new habitats have been discovered in
recent decades. One example is illustrated by deepwater
corals providing a habitat for a great number of other
organisms. These communities are in danger as a result
of increased commercial use of living and nonliving
deepwater resources on the ocean margins, particularly
deep-sea fishing and oil and gas production. Recently discussions have begun regarding the exploration of metals
from the deep sea. This planned exploration must be combined with careful monitoring of the deep-sea environment.
Cold-water corals
Over the past several decades, reef-forming cold-water
corals have been intensively studied (see “Reefs
(Biogenic)”). They are comparable in extent and diversity
to tropical coral reefs. Together with the two dominant
species, Lophelia pertusa and Madrepora oculata, more
than 1,000 other species were identified living in the
cold-water coral environments (Freiwald and Roberts,
2005). Ocean margins contain a large number of different
habitats and biological environments. Because ocean margins are increasingly being used for fisheries, as a biological resource, and for the exploitation of oil, gas, and
minerals, management of the environment and
establishment of conservation areas are under discussion
(e.g., coral reefs off Norway).
Deep biosphere
In addition to these previously unknown ecosystems, significantly more important systems, quantitatively, have
been discovered within the depths of the sediments (see
“Deep Biosphere”). The presence of a rich bacterial life
below the seafloor has been identified, reaching a sediment depth of more than 1,000 m and penetrating even
into the volcanic rocks below the sediment cover. It is estimated that this newly discovered ecosystem accounts for
up to 10 % of the active global biomass.
Human usage
The most obvious impacts of human usage on the oceans
are naturally seen in the coastal regions. As the transition
area between land and sea, the coastal zones are becoming
more and more threatened by increasing intensive use as
residential or industrial areas and as agri- and aquacultural
areas. Added to this are the pressures of harbor sites and
tourism. Already today, 60 % of the world’s population
lives in this zone, and 75 % of all cities with populations
over 2.5 million are located in estuarine regions (see “Integrated Coastal Zone Management”).
In addition to the input of pollutants and nutrients to the
coastal waters, they are increasingly being directly used
for human activities in which clear traces of the use
remain. The shore, banks and shallow-water areas are
being altered by construction (e.g., dikes, harbors, and
pipelines, as well as river-bottom deepening and river correction and gravel and sand removal), which has a lasting
effect on the current conditions, sea-level change
(absolute level and storm-flood frequency), and rates of
erosion and deposition (see “Coastal Engineering” and
“Engineered Coasts”).
On the seaside of the coastal zone, the wide continental
shelf is exploited by fisheries and marine mining (see
“Marine Mineral Resources”). The shelf regions represent
high-productivity regions for fisheries, with 95 % of the
total global catch coming from this zone. They are also
easily accessible for marine mining, especially for the production of oil and gas, as well as gravel and other building
materials. Oil exploration and especially the fisheries have
also begun to advance out onto the continental slope. Fishery activity particularly contributes to large-scale changes
on the seafloor through intensive bottom trawling. This
leads, e.g., to the endangerment of unique ecosystems
such as the cold-water coral reefs that occur on the continental slopes in water depths up to 1,000 m.
Conclusions
Ocean margins are extremely important for mankind due
to their great commercial potential for hydrocarbon exploration and fisheries. On the other hand, these areas possess
a high risk of hazards in the form of earthquakes and
tsunamis. Increasing human activities, including
OCEAN MARGIN SYSTEMS
557