428
Hjalmar THIEL
about 67ºN and 67º40
N) on the continental slope
of the Norwegian Sea at a depth of 976 m and on
the adjacent Vøring Plateau at a depth of 1426 m.
The samples were analyzed several months later for
radiocesium, and high levels of the radionuclides Cs
134
and Cs
137 were discovered in both samples. Bioturbation had carried this material about 10 mm into the
sediment. Further analysis of the material proved that
the radionuclides had originated from the Chernobyl
accident on 26th April 1986. Strong fallout occurred
on 10th and 11th May on Greenland and Svalbard,
and it may be assumed that radioactive material had
already contaminated the surface of the Norwegian
Sea. Organic matter may have scavenged the cesium,
and fast-sinking aggregates may have transported the
material to the seafloor. This is an example of deep-sea
contamination which can be traced back to its origin,
and it can be confidently assumed that larger areas of
the bathyal and the abyssal floors of the Norwegian and
the Greenland Seas received radionuclides during the
spring of 1986. By 1987 cesium-134 derived from the
Chernobyl accident had certainly penetrated into the
water column to a depth of 1000 m near the northern
slope of the Barents Sea and to about 300 m in the
adjacent Nansen Basin (Scholten et al., 1995).
Other fallout events originated from nuclear bomb
tests. Nies (1988, 1989) presented vertical profiles
through the water column in the Northeast Atlantic for
cesium-137, strontium-90, tritium and plutonium-239/
240. Although the highest concentrations were found
in surface and subsurface waters, down to depths of
more than 1000 m, these radionuclides could be traced
to abyssal depths. Their vertical distribution depends
partly on their reactivity with particulate matter. The
concentrations of Cs-137 and Pu-239/240 in some
instances show an increase in the nepheloid layer
above the seafloor. However, for his most westerly
samples (25ºW) Nies (1988) assumed that the higher
values near the bottom originated from northern
subpolar water-masses – that is, from sources other
than fallout in the general area. In possible support
of this conclusion, Scholten et al. (1995) discovered
Cs-137, derived from atmospheric testing of atomic
weapons and from the nuclear reprocessing facility at
Sellafield, mixed throughout the water column in the
Arctic Ocean. These water masses are those which will
be transported into the Atlantic, and later the Indian
and Pacific Oceans, together with their contamination
load.
Although not specifically related to the deep sea,
Kautsky (1988) summarized data collected in 1979, and
between 1982 and 1985, on the distribution of Cs-134
and Cs-137 in surface waters of the Northeast Atlantic,
the North Sea and the Norwegian and Greenland Seas.
He traced the transport routes from their sources, the
nuclear fuel reprocessing plants of Sellafield on the
Irish Sea and La Hague on the English Channel, all
the way through the North Sea, the Norwegian Sea,
into the Barents Sea and to the Greenland Sea (see
also Kershaw and Baxter, 1995). There, the water may
be entrained into the downwelling processes (Rudels
and Quadfasel, 1991; Schlosser et al., 1995a). It is
this down-welled water with a high density which
leaves the Norwegian and Greenland Seas, passing
the Shetland–Greenland ridge, and contributing to the
North Atlantic Bottom Water. Aarkrog et al. (1983,
1987) had calculated the transport time for the surface
waters from Sellafield to the Greenland Sea to be seven
years, Kautsky (1987) reported 7–9 years, and Nyffeler
et al. (1996) 7–10 years. Adding to this the transport
time from the Greenland Sea to the North Atlantic deep
sea, probably in the same time range, the total time
from Sellafield or La Hague to the deep ocean would
still be well below the 30.2 years half-life of Cs-137.
This very rough calculation demonstrates that contaminants from terrestrial sources, if they are persistent
and not deposited somewhere in shallow sediments,
will reach the deep sea. Nies (1988) had discovered
Cs-137 values in the bottom water layer to be higher
than in the water column above. This is the North
Atlantic Bottom Water which carries the signature
of the water from Sellafield and La Hague. Other
contaminants may originate from dumping sites in
shallow water in Northern Siberia, and from rivers
discharging into the Arctic Ocean (Khodakovsky,
1994; Nies et al., 1997). These contaminants may be
transported into the deep Arctic basins by downslope
convection. Indications from radionuclides for deep
convection are presented by Cochran et al. (1995)
and Wedekind et al. (1997) for the Norwegian and
Greenland Seas, by Papucci et al. (1996, 2000),
Yiou et al. (1997) and Merino et al. (1997) for the
Mediterranean, and by Gulin et al. (1997) for the Black
Sea. The tracers originated partly from the Chernobyl
accident.
Chlorofluorocarbons
A number of substances exist today which are useful
tracers for tracking water masses (Roether and Rhein,
Hjalmar THIEL
about 67ºN and 67º40
N) on the continental slope
of the Norwegian Sea at a depth of 976 m and on
the adjacent Vøring Plateau at a depth of 1426 m.
The samples were analyzed several months later for
radiocesium, and high levels of the radionuclides Cs
134
and Cs
137 were discovered in both samples. Bioturbation had carried this material about 10 mm into the
sediment. Further analysis of the material proved that
the radionuclides had originated from the Chernobyl
accident on 26th April 1986. Strong fallout occurred
on 10th and 11th May on Greenland and Svalbard,
and it may be assumed that radioactive material had
already contaminated the surface of the Norwegian
Sea. Organic matter may have scavenged the cesium,
and fast-sinking aggregates may have transported the
material to the seafloor. This is an example of deep-sea
contamination which can be traced back to its origin,
and it can be confidently assumed that larger areas of
the bathyal and the abyssal floors of the Norwegian and
the Greenland Seas received radionuclides during the
spring of 1986. By 1987 cesium-134 derived from the
Chernobyl accident had certainly penetrated into the
water column to a depth of 1000 m near the northern
slope of the Barents Sea and to about 300 m in the
adjacent Nansen Basin (Scholten et al., 1995).
Other fallout events originated from nuclear bomb
tests. Nies (1988, 1989) presented vertical profiles
through the water column in the Northeast Atlantic for
cesium-137, strontium-90, tritium and plutonium-239/
240. Although the highest concentrations were found
in surface and subsurface waters, down to depths of
more than 1000 m, these radionuclides could be traced
to abyssal depths. Their vertical distribution depends
partly on their reactivity with particulate matter. The
concentrations of Cs-137 and Pu-239/240 in some
instances show an increase in the nepheloid layer
above the seafloor. However, for his most westerly
samples (25ºW) Nies (1988) assumed that the higher
values near the bottom originated from northern
subpolar water-masses – that is, from sources other
than fallout in the general area. In possible support
of this conclusion, Scholten et al. (1995) discovered
Cs-137, derived from atmospheric testing of atomic
weapons and from the nuclear reprocessing facility at
Sellafield, mixed throughout the water column in the
Arctic Ocean. These water masses are those which will
be transported into the Atlantic, and later the Indian
and Pacific Oceans, together with their contamination
load.
Although not specifically related to the deep sea,
Kautsky (1988) summarized data collected in 1979, and
between 1982 and 1985, on the distribution of Cs-134
and Cs-137 in surface waters of the Northeast Atlantic,
the North Sea and the Norwegian and Greenland Seas.
He traced the transport routes from their sources, the
nuclear fuel reprocessing plants of Sellafield on the
Irish Sea and La Hague on the English Channel, all
the way through the North Sea, the Norwegian Sea,
into the Barents Sea and to the Greenland Sea (see
also Kershaw and Baxter, 1995). There, the water may
be entrained into the downwelling processes (Rudels
and Quadfasel, 1991; Schlosser et al., 1995a). It is
this down-welled water with a high density which
leaves the Norwegian and Greenland Seas, passing
the Shetland–Greenland ridge, and contributing to the
North Atlantic Bottom Water. Aarkrog et al. (1983,
1987) had calculated the transport time for the surface
waters from Sellafield to the Greenland Sea to be seven
years, Kautsky (1987) reported 7–9 years, and Nyffeler
et al. (1996) 7–10 years. Adding to this the transport
time from the Greenland Sea to the North Atlantic deep
sea, probably in the same time range, the total time
from Sellafield or La Hague to the deep ocean would
still be well below the 30.2 years half-life of Cs-137.
This very rough calculation demonstrates that contaminants from terrestrial sources, if they are persistent
and not deposited somewhere in shallow sediments,
will reach the deep sea. Nies (1988) had discovered
Cs-137 values in the bottom water layer to be higher
than in the water column above. This is the North
Atlantic Bottom Water which carries the signature
of the water from Sellafield and La Hague. Other
contaminants may originate from dumping sites in
shallow water in Northern Siberia, and from rivers
discharging into the Arctic Ocean (Khodakovsky,
1994; Nies et al., 1997). These contaminants may be
transported into the deep Arctic basins by downslope
convection. Indications from radionuclides for deep
convection are presented by Cochran et al. (1995)
and Wedekind et al. (1997) for the Norwegian and
Greenland Seas, by Papucci et al. (1996, 2000),
Yiou et al. (1997) and Merino et al. (1997) for the
Mediterranean, and by Gulin et al. (1997) for the Black
Sea. The tracers originated partly from the Chernobyl
accident.
Chlorofluorocarbons
A number of substances exist today which are useful
tracers for tracking water masses (Roether and Rhein,