ANTHROPOGENIC IMPACTS ON THE DEEP SEA
445
– solid and liquid: >~400 m, <11ºC.
The solid/liquid state occurs in the form of hydrates
or clathrates, a crystallization of carbon dioxide and
water where they have a common interface. At >600 m
and deep-sea temperatures of 2–3ºC the carbon dioxide
freezes to the solid form. Another important factor is
the density of liquid carbon dioxide, which is higher
than that of the ambient water at depths greater than
3700 m.
Ocean storage would use the liquid or the solid/liquid
phase of the waste, through dispersion and dissolution
in the bathyal or abyssal deep water column or on
the abyssal sea floor as a liquid lake or in the solid
form (“dry ice”). The time delay for the return of
this carbon dioxide to the ocean surface and the
atmosphere depends on the oceanographic conditions
of the region and on the depth of disposal. Liquid
and solid carbon dioxide will dissolve in the water
mass, and the question of how long the isolation will
be effective depends on the rate of dissolution. The
disposal of carbon dioxide in liquid or solid form would
therefore be equivalent to “delayed dissolution”.
The discharge of liquid carbon dioxide could be
achieved by a riser similar to those described for the
delivery of muds to the seafloor (Adams et al., 1995;
Kajishima et al., 1995), or by suspending a towed pipe
and spraying mechanism for a wider distribution of
droplets in the water column to aid dissolution. Solid
carbon dioxide could be dropped in streamlined “dry
ice” missiles, but during their descent much of the
carbon dioxide might dissolve in the water column.
This mode of disposal is unlikely to be employed,
however, since the freezing process consumes a great
deal of energy, and thus would lead to the generation
of more greenhouse gas.
Carbon dioxide in the ocean is finely balanced
with the carbonate system, and its introduction into
the water column or onto the seafloor would lower
the pH. Whereas production processes in the ocean
surface are responsible for a certain variability of pH,
with a seasonal amplitude of about 0.1 pH unit, the
level in the deep sea is very stable and organisms
are likely to be sensitive to minor changes. Ocean
values of pH generally range between 7.7 and 8.2
(Brewer et al., 1995). A decrease would be detrimental
to organisms, and below pH 6.5 organisms would
be killed (Magnesen and Wahl, 1993; P¨ ortner and
Reipschl¨ ager, 1996; Stenevik and Giske, 1997; Omori
et al., 1998). Sublethal effects of a decrease in pH
would be associated with the exchange and transport
of respiratory gases, and would lead to modifications
in community structure and ecological processes.
Creating a lake of carbon dioxide in a depression of
the deep seafloor would certainly destroy all benthic
life. Benthopelagic species would be impacted during
the disposal, but there would be an additional longterm effect, since migratory species on their path to the
seafloor might penetrate into the dissolution zone above
the lake, or the lake itself, and would be trapped, unless
they have the ability to swim up again and escape into
the non-impacted neighbourhood. The dissolution of
carbonates through the introduction of carbon dioxide
would probably reduce the amount of carbon dioxide,
but this would have little overall effect.
A similar fate for organisms can be expected if
liquid carbon dioxide is allowed to flow down any
slope into deeper regions; organisms would be killed,
and carbonate components of the sediment might be
dissolved along the track, eroding a channel into the
seafloor. This could even lead to the destabilization of
the slope sediments.
Liquid carbon dioxide released into the water column
from a ship in passage would initially create a plume
with a dissolution zone extending over a few hundred
metres vertically and a few tens of metres horizontally
at the current speed of 10 cm s
−1 typically measured
at great depths. A pH reduction of 2–3 may occur in
the core of the plume, and again this may be lethal or
sublethal for organisms. Mobile species may be able to
escape such an impact on the water body. Dissolution
away from the plume would gradually reduce the
change in pH to tolerable levels.
As in the case of benthopelagic species, migration
of plankton must also be considered. Vertical diel
migration is intensive down to a depth of 1000 m,
but in decapod Crustacea extends to 1200 m, and in
lantern fish even to 1500 m. Seasonal and ontogenetic
migrations may penetrate even greater depths, and it
must be assumed that a layer of lowered pH might
greatly disturb migrators of all age classes.
Carbon dioxide has been rarely considered as an
ecological variable, and relatively little is known about
the effects on organisms of higher concentrations of
this gas in the natural environment (P¨ ortner and Reipschl¨ ager, 1996). Experimental research on different
scales could be conceived, in order to learn about
the effects of potential changes in the ocean system.
Small-scale investigations may be conducted in the
laboratory to test the reaction of single species in
aquaria or communities in mesocosms. However, it
445
– solid and liquid: >~400 m, <11ºC.
The solid/liquid state occurs in the form of hydrates
or clathrates, a crystallization of carbon dioxide and
water where they have a common interface. At >600 m
and deep-sea temperatures of 2–3ºC the carbon dioxide
freezes to the solid form. Another important factor is
the density of liquid carbon dioxide, which is higher
than that of the ambient water at depths greater than
3700 m.
Ocean storage would use the liquid or the solid/liquid
phase of the waste, through dispersion and dissolution
in the bathyal or abyssal deep water column or on
the abyssal sea floor as a liquid lake or in the solid
form (“dry ice”). The time delay for the return of
this carbon dioxide to the ocean surface and the
atmosphere depends on the oceanographic conditions
of the region and on the depth of disposal. Liquid
and solid carbon dioxide will dissolve in the water
mass, and the question of how long the isolation will
be effective depends on the rate of dissolution. The
disposal of carbon dioxide in liquid or solid form would
therefore be equivalent to “delayed dissolution”.
The discharge of liquid carbon dioxide could be
achieved by a riser similar to those described for the
delivery of muds to the seafloor (Adams et al., 1995;
Kajishima et al., 1995), or by suspending a towed pipe
and spraying mechanism for a wider distribution of
droplets in the water column to aid dissolution. Solid
carbon dioxide could be dropped in streamlined “dry
ice” missiles, but during their descent much of the
carbon dioxide might dissolve in the water column.
This mode of disposal is unlikely to be employed,
however, since the freezing process consumes a great
deal of energy, and thus would lead to the generation
of more greenhouse gas.
Carbon dioxide in the ocean is finely balanced
with the carbonate system, and its introduction into
the water column or onto the seafloor would lower
the pH. Whereas production processes in the ocean
surface are responsible for a certain variability of pH,
with a seasonal amplitude of about 0.1 pH unit, the
level in the deep sea is very stable and organisms
are likely to be sensitive to minor changes. Ocean
values of pH generally range between 7.7 and 8.2
(Brewer et al., 1995). A decrease would be detrimental
to organisms, and below pH 6.5 organisms would
be killed (Magnesen and Wahl, 1993; P¨ ortner and
Reipschl¨ ager, 1996; Stenevik and Giske, 1997; Omori
et al., 1998). Sublethal effects of a decrease in pH
would be associated with the exchange and transport
of respiratory gases, and would lead to modifications
in community structure and ecological processes.
Creating a lake of carbon dioxide in a depression of
the deep seafloor would certainly destroy all benthic
life. Benthopelagic species would be impacted during
the disposal, but there would be an additional longterm effect, since migratory species on their path to the
seafloor might penetrate into the dissolution zone above
the lake, or the lake itself, and would be trapped, unless
they have the ability to swim up again and escape into
the non-impacted neighbourhood. The dissolution of
carbonates through the introduction of carbon dioxide
would probably reduce the amount of carbon dioxide,
but this would have little overall effect.
A similar fate for organisms can be expected if
liquid carbon dioxide is allowed to flow down any
slope into deeper regions; organisms would be killed,
and carbonate components of the sediment might be
dissolved along the track, eroding a channel into the
seafloor. This could even lead to the destabilization of
the slope sediments.
Liquid carbon dioxide released into the water column
from a ship in passage would initially create a plume
with a dissolution zone extending over a few hundred
metres vertically and a few tens of metres horizontally
at the current speed of 10 cm s
−1 typically measured
at great depths. A pH reduction of 2–3 may occur in
the core of the plume, and again this may be lethal or
sublethal for organisms. Mobile species may be able to
escape such an impact on the water body. Dissolution
away from the plume would gradually reduce the
change in pH to tolerable levels.
As in the case of benthopelagic species, migration
of plankton must also be considered. Vertical diel
migration is intensive down to a depth of 1000 m,
but in decapod Crustacea extends to 1200 m, and in
lantern fish even to 1500 m. Seasonal and ontogenetic
migrations may penetrate even greater depths, and it
must be assumed that a layer of lowered pH might
greatly disturb migrators of all age classes.
Carbon dioxide has been rarely considered as an
ecological variable, and relatively little is known about
the effects on organisms of higher concentrations of
this gas in the natural environment (P¨ ortner and Reipschl¨ ager, 1996). Experimental research on different
scales could be conceived, in order to learn about
the effects of potential changes in the ocean system.
Small-scale investigations may be conducted in the
laboratory to test the reaction of single species in
aquaria or communities in mesocosms. However, it