ANTHROPOGENIC IMPACTS ON THE DEEP SEA
431
Although these events are rare in ecological terms,
the amounts transferred into the deep ocean may be
very large (Seibold and Berger, 1993). Quadfasel et al.
(1990) reported the existence of turbidity currents in
the Sulu Sea at intervals of several decades following
long-term sediment accumulation.
Various other means of contaminant transport occur,
although these may be rather weak and geographically
limited. Contaminants scavenged during the freezing
process together with sedimentary materials, or those
precipitated on ice floes in polar seas, may be released
from the ice cover into the ocean by the melting
process, together with particulate matter, after drifting
long distances over several years. Other contaminants
are drained out of the ice much faster, together
with salt brines concentrated during freezing (Arctic
Monitoring and Assessment Programme, 1998). Absorbed to particulate matter, they settle to the seafloor.
Those in solution are transported with the currents,
and downwards-directed convection with cold water
transfers them into deep water.
Quadfasel et al. (1988) and Fohrmann (1996)
described and modelled the occurrence of sedimentladen or turbidity plumes, originating from melting ice
and the release of the particulate load from ice floes,
in the Arctic. Both types of plume probably drifted
to the Svalbard and Bear Island regions from the far
northern regions of Siberia, with added components
from fallout of contaminants with snow. Because of
its higher density, this particle-laden water mass sinks
to great depth. The particulate matter is lost during
this passage through the basin, predominantly along the
continental slope of the northern Norwegian Sea and
the Barents Sea, where further cold water masses from
the shelf penetrate into the deep sea (Rutgers van der
Loeff et al., 1995). Adsorbed reactive contaminants are
distributed at the sediment surface below the paths of
the currents.
Another example of downslope transport is known
from upwelling areas, for instance off northwestern
Africa. Primary organic matter (determined as chlorophyll a and its degradation products) and benthic organisms have their maximum downslope concentration
at depths between 800 m and 1000 m – an unexpected
increase with increasing depth (Thiel, 1982). Support
for the deduction that food energy is transported may be
derived from the existence of turbid bottom water layers
(Kullenberg, 1978) and from indications of downslope
transport of sediment (Bein and F¨ utterer, 1977). These
phenomena may be partially explained by a downslope
component of the undercurrent flowing to the north
along the upper continental slope (Mittelstaedt, 1982),
and internal waves may regularly interact with the
upper slope, resulting in the resuspension of particulate
matter (Fahrbach and Meincke, 1982). Downslope
transport of water and particles was also observed by
Thomsen and van Weering (1998) along a transect
south of the Porcupine Seabight in the northeast
Atlantic.
This short account of existing and potential contaminants in and pathways into the deep sea is far from
comprehensive (see also OSPARCOM, 2000a,b,c).
There are more results available from other ocean
regions and more detailed descriptions of the processes involved. However, it shows that a variety of
transfer mechanisms exist by which contaminants not
visible to the human eye reach the deep sea. Their
concentrations have so far not reached unacceptable
levels (Ballschmiter et al., 1997) so that they cannot
be classified as pollutants; but from the data available it seems that no region of the deep sea has
escaped anthropogenic impact. No results are available
from deep-sea trenches, but since vertical sinking is
independent of depth and most trenches are situated
close to the continents and to island arcs, and because
some water renewal occurs down to maximum depths,
contaminants are ubiquitous throughout the oceans.
VISIBLE AND CONSCIOUS CONTAMINATION
In contrast to the non-visible substances in the sea,
visible contamination ranges from items of small litter
thrown overboard by seamen and tourists to regular
ocean disposal using the deep sea as a repository.
This category includes deep-sea mining and fishing.
Primarily, ore is extracted from the deep seafloor, but
much of the material mined is discharged back into
the ocean. Both disposal of wastes and mining of
mineral resources must be economically feasible and
therefore can be organized only on the basis of largescale intrusions including the mobilization of large
amounts of material. Fishing, if it is to be profitable,
may not be sustainable at great depth. All these uses
of the deep sea may have long-lasting and far-reaching
effects.
The regular thoughtless and secret dumping of
wastes at sea
Ever since man first crossed the oceans, the sea has
431
Although these events are rare in ecological terms,
the amounts transferred into the deep ocean may be
very large (Seibold and Berger, 1993). Quadfasel et al.
(1990) reported the existence of turbidity currents in
the Sulu Sea at intervals of several decades following
long-term sediment accumulation.
Various other means of contaminant transport occur,
although these may be rather weak and geographically
limited. Contaminants scavenged during the freezing
process together with sedimentary materials, or those
precipitated on ice floes in polar seas, may be released
from the ice cover into the ocean by the melting
process, together with particulate matter, after drifting
long distances over several years. Other contaminants
are drained out of the ice much faster, together
with salt brines concentrated during freezing (Arctic
Monitoring and Assessment Programme, 1998). Absorbed to particulate matter, they settle to the seafloor.
Those in solution are transported with the currents,
and downwards-directed convection with cold water
transfers them into deep water.
Quadfasel et al. (1988) and Fohrmann (1996)
described and modelled the occurrence of sedimentladen or turbidity plumes, originating from melting ice
and the release of the particulate load from ice floes,
in the Arctic. Both types of plume probably drifted
to the Svalbard and Bear Island regions from the far
northern regions of Siberia, with added components
from fallout of contaminants with snow. Because of
its higher density, this particle-laden water mass sinks
to great depth. The particulate matter is lost during
this passage through the basin, predominantly along the
continental slope of the northern Norwegian Sea and
the Barents Sea, where further cold water masses from
the shelf penetrate into the deep sea (Rutgers van der
Loeff et al., 1995). Adsorbed reactive contaminants are
distributed at the sediment surface below the paths of
the currents.
Another example of downslope transport is known
from upwelling areas, for instance off northwestern
Africa. Primary organic matter (determined as chlorophyll a and its degradation products) and benthic organisms have their maximum downslope concentration
at depths between 800 m and 1000 m – an unexpected
increase with increasing depth (Thiel, 1982). Support
for the deduction that food energy is transported may be
derived from the existence of turbid bottom water layers
(Kullenberg, 1978) and from indications of downslope
transport of sediment (Bein and F¨ utterer, 1977). These
phenomena may be partially explained by a downslope
component of the undercurrent flowing to the north
along the upper continental slope (Mittelstaedt, 1982),
and internal waves may regularly interact with the
upper slope, resulting in the resuspension of particulate
matter (Fahrbach and Meincke, 1982). Downslope
transport of water and particles was also observed by
Thomsen and van Weering (1998) along a transect
south of the Porcupine Seabight in the northeast
Atlantic.
This short account of existing and potential contaminants in and pathways into the deep sea is far from
comprehensive (see also OSPARCOM, 2000a,b,c).
There are more results available from other ocean
regions and more detailed descriptions of the processes involved. However, it shows that a variety of
transfer mechanisms exist by which contaminants not
visible to the human eye reach the deep sea. Their
concentrations have so far not reached unacceptable
levels (Ballschmiter et al., 1997) so that they cannot
be classified as pollutants; but from the data available it seems that no region of the deep sea has
escaped anthropogenic impact. No results are available
from deep-sea trenches, but since vertical sinking is
independent of depth and most trenches are situated
close to the continents and to island arcs, and because
some water renewal occurs down to maximum depths,
contaminants are ubiquitous throughout the oceans.
VISIBLE AND CONSCIOUS CONTAMINATION
In contrast to the non-visible substances in the sea,
visible contamination ranges from items of small litter
thrown overboard by seamen and tourists to regular
ocean disposal using the deep sea as a repository.
This category includes deep-sea mining and fishing.
Primarily, ore is extracted from the deep seafloor, but
much of the material mined is discharged back into
the ocean. Both disposal of wastes and mining of
mineral resources must be economically feasible and
therefore can be organized only on the basis of largescale intrusions including the mobilization of large
amounts of material. Fishing, if it is to be profitable,
may not be sustainable at great depth. All these uses
of the deep sea may have long-lasting and far-reaching
effects.
The regular thoughtless and secret dumping of
wastes at sea
Ever since man first crossed the oceans, the sea has