320
Riihlemann et al.
paleoproductivity in the glacial Southern Ocean,
however, was probably comparable to the modem
conditions (Charles et al. 1991; Niirnberg et al.
1997; Francois et al. 1997). Paleoproductivity in the
Arctic Sea was lowered during the last Glacial
caused by increased sea-ice extension (Schubert
and Stein 1996; Knies and Stein 1998).
4. Oligotrophic ocean areas. Paleoproductivity
remained nearly constant during glacials and
interglacials or decreased slightly in the low productivity open ocean during glacials (Samthein et
al. 1988; Mix 1989; Francois et al. 1990; Howard
and Prell 1994; Riihlemann et al. 1996; van Kreveld
et al. 1996).
Factors Influencing Organic Carbon
Preservation
Numerous studies on the fate of organic carbon
after its production in the surface water have been
published (see reviews in Emerson and Hedges
1988; Berger et al. 1989a; Stein 1991; Engel and
Macko 1993; Canfield 1994; Hedges and Keil
1995). They indicate that the proportion of organic
matter that escapes decomposition and becomes
preserved in marine sediments depends mainly on
the quantity, quality, and seasonality of primary
production (which ultimately limits the export production and the flux to the sea floor), on water
depth, sedimentation rate, and on the sedimentary
redox environment.
Export Production and Seasonality
The export production (XP) increases non-linearly
with increasing primary production (PP) (Eppley
and Peterson 1979). According to Berger and
Wefer (1990), the export factor (XP/PP) can be
estimated from primary production by
XF=2 . .JPP
(1 )
with XF [%] and PP [gC m· 2 a· l ]
This definition of the export factor assumes that
primary production occurs at a constant rate
throughout the year. In nature, however, all productivity systems show more or less seasonal and
interannual variability (Wefer 1989). This variability in primary production controls the quantity of export production (Platt and Harrison 1985; Berger
and Wefer 1990). Any ocean area which is governed by more seasonal or even strongly pulsed
production has a higher output percentage than an
area with a more constant production, provided the
annually averaged productivity is the same at both
sites (Fig. 3). In the case of high seasonality, heterotrophic organisms are less efficient in decomposing organic carbon, whereas they are better
adapted in case oflow seasonality when recycling
needs to be more efficient and regenerated production prevails (Berger et al. 1989b). To characterize the temporal variability of primary production,
Berger and Wefer (1990) introduced the seasonality
index (SI) derived from the production half-time (expressed in terms ofthe number of months it takes
to generate one half of the annual production).
They postulated that the export factor increases
with primary production and seasonality, in the form
of
XF = 2 • .JPP (1 + (SI + I )4/1 000)
(2)
Vertical Flux and Burial of Particulate
OrganiC Carbon
After leaving the euphotic zone particulate organic
matter settling through the water column is further
decomposed by heterotrophic organisms. Several
empirically derived equations have been published
to estimate the vertical particulate organic carbon
flux as a function of primary production and water
depth (Suess 1980; Betzer et al. 1984; Berger et
al. 1987; Pace et al. 1987, see Bishop 1989 for a
review). The equation given by Betzer et al. (1984)
J = 0.409 . ppl.41 . Z·0628
(3)
reveals that most particulate organic matter exported to depth is already remineralized within the
upper few hundred meters and that only 1 to 3%
of the organic carbon produced in the surface layer
ever reaches bathyal and abyssal depths (Fig. 4).
At the sediment-water interface, a large fraction of the organic carbon is further decomposed
within a few months leaving only the most resistant organic compounds to be buried within the sedi-
Riihlemann et al.
paleoproductivity in the glacial Southern Ocean,
however, was probably comparable to the modem
conditions (Charles et al. 1991; Niirnberg et al.
1997; Francois et al. 1997). Paleoproductivity in the
Arctic Sea was lowered during the last Glacial
caused by increased sea-ice extension (Schubert
and Stein 1996; Knies and Stein 1998).
4. Oligotrophic ocean areas. Paleoproductivity
remained nearly constant during glacials and
interglacials or decreased slightly in the low productivity open ocean during glacials (Samthein et
al. 1988; Mix 1989; Francois et al. 1990; Howard
and Prell 1994; Riihlemann et al. 1996; van Kreveld
et al. 1996).
Factors Influencing Organic Carbon
Preservation
Numerous studies on the fate of organic carbon
after its production in the surface water have been
published (see reviews in Emerson and Hedges
1988; Berger et al. 1989a; Stein 1991; Engel and
Macko 1993; Canfield 1994; Hedges and Keil
1995). They indicate that the proportion of organic
matter that escapes decomposition and becomes
preserved in marine sediments depends mainly on
the quantity, quality, and seasonality of primary
production (which ultimately limits the export production and the flux to the sea floor), on water
depth, sedimentation rate, and on the sedimentary
redox environment.
Export Production and Seasonality
The export production (XP) increases non-linearly
with increasing primary production (PP) (Eppley
and Peterson 1979). According to Berger and
Wefer (1990), the export factor (XP/PP) can be
estimated from primary production by
XF=2 . .JPP
(1 )
with XF [%] and PP [gC m· 2 a· l ]
This definition of the export factor assumes that
primary production occurs at a constant rate
throughout the year. In nature, however, all productivity systems show more or less seasonal and
interannual variability (Wefer 1989). This variability in primary production controls the quantity of export production (Platt and Harrison 1985; Berger
and Wefer 1990). Any ocean area which is governed by more seasonal or even strongly pulsed
production has a higher output percentage than an
area with a more constant production, provided the
annually averaged productivity is the same at both
sites (Fig. 3). In the case of high seasonality, heterotrophic organisms are less efficient in decomposing organic carbon, whereas they are better
adapted in case oflow seasonality when recycling
needs to be more efficient and regenerated production prevails (Berger et al. 1989b). To characterize the temporal variability of primary production,
Berger and Wefer (1990) introduced the seasonality
index (SI) derived from the production half-time (expressed in terms ofthe number of months it takes
to generate one half of the annual production).
They postulated that the export factor increases
with primary production and seasonality, in the form
of
XF = 2 • .JPP (1 + (SI + I )4/1 000)
(2)
Vertical Flux and Burial of Particulate
OrganiC Carbon
After leaving the euphotic zone particulate organic
matter settling through the water column is further
decomposed by heterotrophic organisms. Several
empirically derived equations have been published
to estimate the vertical particulate organic carbon
flux as a function of primary production and water
depth (Suess 1980; Betzer et al. 1984; Berger et
al. 1987; Pace et al. 1987, see Bishop 1989 for a
review). The equation given by Betzer et al. (1984)
J = 0.409 . ppl.41 . Z·0628
(3)
reveals that most particulate organic matter exported to depth is already remineralized within the
upper few hundred meters and that only 1 to 3%
of the organic carbon produced in the surface layer
ever reaches bathyal and abyssal depths (Fig. 4).
At the sediment-water interface, a large fraction of the organic carbon is further decomposed
within a few months leaving only the most resistant organic compounds to be buried within the sedi-