24
Weferetal.
flux caught in traps below the surface layer. It is
similar to "new production" (sensu Dugdale and
Goering 1967) in that, on the whole, the export depends on the supply of nitrate to the photic zone. It
is the export production that determines the intensity of the oxygen minimum zone (Suess 1980).
Geochemists and geologists are especially interested in the flux of organic carbon into the sediment, that is, the organic carbon accumulation. This
carbon is sequestered from the ocean and therefore its accumulation influences the content of
carbon in the ocean-atmosphere system, with implications for pC0 2 (Vincent and Berger 1985 ;
Samthein et al. 1988).
Generally speaking, there is a relationship between productivity in surface waters and organic
carbon accumulation in underlying sediments (e.g.
Samthein et al.I992a). Below the central gyres, the
deserts of the ocean, organic carbon content in
sediments is extremely low. In upwelling areas, the
organic carbon content is high, and, in many cases,
Fe·Mg·illite,
fossil kaolinile
2000
4000
70'
chlorite, smactne,
well-ordered AI·llllte
source: Andean mobile
belt (Antarctic Peninsula,
Patgonia)
50'
sufficient for sulfate reduction and pyrite formation. From this observation, it may be expected that
at anyone place a change in the content of organic
carbon indicates a change in productivity through
time. This principle was first quantified by MUller
and Suess (1979) and has found much application
since (MUller et al. 1983; Samthein et al. 1987,
1992a; Lyle et al. 1992, among others).
The range of variation in productivity of surface
waters spans roughly a factor of 10 (excluding
estuaries and inner shelf), while the content in
sediments varies by, say, a factor of 40. If accumulation rate is considered, the range in sediment
flux increases to greater than 100. It is clear, therefore, that the relationship between productivity and
organic matter accumulation is strongly non-linear
(Berger and Herguera 1992). In anyone place,
changes in sedimentation rate are commonly much
smaller than changes in organic matter content.
Neglecting sedimentation rate (which has the advantage of avoiding serious mistakes in assigning
30'
20' S source: equal. Africa
Fig. 14, Simplified model of sources and transport pathways of clay minerals related to deep-water circulation in
the South Atlantic. From Diekmann et al. (1996).
Weferetal.
flux caught in traps below the surface layer. It is
similar to "new production" (sensu Dugdale and
Goering 1967) in that, on the whole, the export depends on the supply of nitrate to the photic zone. It
is the export production that determines the intensity of the oxygen minimum zone (Suess 1980).
Geochemists and geologists are especially interested in the flux of organic carbon into the sediment, that is, the organic carbon accumulation. This
carbon is sequestered from the ocean and therefore its accumulation influences the content of
carbon in the ocean-atmosphere system, with implications for pC0 2 (Vincent and Berger 1985 ;
Samthein et al. 1988).
Generally speaking, there is a relationship between productivity in surface waters and organic
carbon accumulation in underlying sediments (e.g.
Samthein et al.I992a). Below the central gyres, the
deserts of the ocean, organic carbon content in
sediments is extremely low. In upwelling areas, the
organic carbon content is high, and, in many cases,
Fe·Mg·illite,
fossil kaolinile
2000
4000
70'
chlorite, smactne,
well-ordered AI·llllte
source: Andean mobile
belt (Antarctic Peninsula,
Patgonia)
50'
sufficient for sulfate reduction and pyrite formation. From this observation, it may be expected that
at anyone place a change in the content of organic
carbon indicates a change in productivity through
time. This principle was first quantified by MUller
and Suess (1979) and has found much application
since (MUller et al. 1983; Samthein et al. 1987,
1992a; Lyle et al. 1992, among others).
The range of variation in productivity of surface
waters spans roughly a factor of 10 (excluding
estuaries and inner shelf), while the content in
sediments varies by, say, a factor of 40. If accumulation rate is considered, the range in sediment
flux increases to greater than 100. It is clear, therefore, that the relationship between productivity and
organic matter accumulation is strongly non-linear
(Berger and Herguera 1992). In anyone place,
changes in sedimentation rate are commonly much
smaller than changes in organic matter content.
Neglecting sedimentation rate (which has the advantage of avoiding serious mistakes in assigning
30'
20' S source: equal. Africa
Fig. 14, Simplified model of sources and transport pathways of clay minerals related to deep-water circulation in
the South Atlantic. From Diekmann et al. (1996).