356
Gingele et al.
Glacial-Interglacial Variations and
Comparison of Paleoproductivity Proxies
Export production (P n ,) based on Ba measurements was calculated for 9 cores of the Atlantic
from the Equator to the Antarctic continental margin
(Fig. 7). Calculations were made using the algorithm of Francois et al. (1995). Pnew computed with
the approach of Dymond et al. (1992) is given for
reasons of comparison for the cores recovered
from the Antarctic continental margin.
Glacial-interglacial changes in export production
are recorded for all cores. At the Equatorial Divergence (GeoB 1041, GeoB 1117) increased production is observed during glacials, due to intensified upwelling forced by stronger glacial winds.
Downcore concentrations of barium coincide well
with organic carbon (Bickert 1992) and lead to similar estimations of paleoproductivity (Gingele and
Dahmke 1994). Concentrations of biogenic silica
(opal) are low and strongly influenced by dissolution (Gingele 1992).
Coastal upwelling off Namibia was also higher
in glacial stages 2-4 (GeoB 1710). The pattern
of biogenic barium in this core is concurrent
with patterns of organic carbon and opal. Benthic
foraminifera assemblages also indicate an
increased input of nutrients during stages 2-4
(Schmiedl 1995).
A pattern of increased glacial productivity can
be observed down to the Subantarctic Zone and is
evidenced in core PS2082 by downcore distributions of organic carbon, opal and assemblages of
productivity-related radiolarians (Brathauer 1996).
In the open ocean environment of the Polar
Frontal Zone (PS 1756) and the Antarctic Zone
(PSI768) higher productivity is recorded in the
Holocene and stage 5, due to the extension of the
high-productivity belt and reduced winter sea-ice
(Niirnberg 1995). Residual concentrations of organic carbon and extensive lateral advection of
material (opal) impede the comparison of productivity proxies here.
At the Antarctic continental margin, productivity increased drastically in the Holocene and peak
warm-stages, reaching values representative of
recent upwelling areas in stage 5.5 (Bonn et al.
1998). In glacial stages, productivity ceased almost
completely due to a permanent sea-ice coverage.
Downcore distributions of organic carbon are rather
featureless in these cores, whereas the opal contents correlate well with concentrations of biogenic
barium (Bonn et al. 1998). However, amplitudes of
opal concentrations decrease with age and the oldest barium peak (stage 11) is no longer matched
by an opal peak in core PS 1821-6.
Summarizing the comparison of proxies from
our selection of cores, it can be said that P calculations, using Ba(b;o) concentrations, ar~wconfirmed by other paleoproductivity proxies. Nevertheless, only biogenic barium can be applied to all
our cores, whereas the other proxies are subject
to limitations by latitude or sedimentary environment.
The comparison ofPn,w from core-top samples
computed according to Francois et al. (1995) with
maps of recent export production (Berger et al.
1989), or with calculations from TOC-accumulation (Bickert 1992), do not show unequivocal results. At the Equatorial Divergence, Pnew computed
according to Francois et al. (1995) is below estimations of recent export production (Berger et al.
1989), whereas Pnew values based on the calculations of Dymond et al. (1992) match recent values
and calculations derived from TOC-accumulation
(Gingele and Dahmke 1994). Holocene Pn,w values calculated from Ba-data in subantarctic waters (Niirnberg 1995) coincide with estimations of
recent export production (Wefer and Fischer 1991 ;
Treguer and van Bennekom 1991). At the Antarctic continental margin, estimations of recent export
production are rare and vary strongly due to strong
seasonality-spiked bloom events which dominate
the production. P ocw calculated from core top samples (5-50 g C m· 2 a·') exceeds values estimated
by Wefer and Fischer (1991) and Treguer and van
Bennekom (1991) near the Antarctic coast (0.5-5
g C m· 2 a· '). However, estimations based on data
from the Lazarev Sea (Gleitz et al. 1994) suggest
15-75 g C m· 2 a· 1 produced in a six-month period
(Bonn 1995). Average interglacial Pn,w values for
cores near the Antarctic coast range from 10-40 g
C m- 2 a-I (Bonn 1995). Generally, the approach of
Francois et al. (1995) yields 30-40% lower values
in peak warm stages as compared to the approach
of Dymond et al. (1992). The lack of sufficient data
Gingele et al.
Glacial-Interglacial Variations and
Comparison of Paleoproductivity Proxies
Export production (P n ,) based on Ba measurements was calculated for 9 cores of the Atlantic
from the Equator to the Antarctic continental margin
(Fig. 7). Calculations were made using the algorithm of Francois et al. (1995). Pnew computed with
the approach of Dymond et al. (1992) is given for
reasons of comparison for the cores recovered
from the Antarctic continental margin.
Glacial-interglacial changes in export production
are recorded for all cores. At the Equatorial Divergence (GeoB 1041, GeoB 1117) increased production is observed during glacials, due to intensified upwelling forced by stronger glacial winds.
Downcore concentrations of barium coincide well
with organic carbon (Bickert 1992) and lead to similar estimations of paleoproductivity (Gingele and
Dahmke 1994). Concentrations of biogenic silica
(opal) are low and strongly influenced by dissolution (Gingele 1992).
Coastal upwelling off Namibia was also higher
in glacial stages 2-4 (GeoB 1710). The pattern
of biogenic barium in this core is concurrent
with patterns of organic carbon and opal. Benthic
foraminifera assemblages also indicate an
increased input of nutrients during stages 2-4
(Schmiedl 1995).
A pattern of increased glacial productivity can
be observed down to the Subantarctic Zone and is
evidenced in core PS2082 by downcore distributions of organic carbon, opal and assemblages of
productivity-related radiolarians (Brathauer 1996).
In the open ocean environment of the Polar
Frontal Zone (PS 1756) and the Antarctic Zone
(PSI768) higher productivity is recorded in the
Holocene and stage 5, due to the extension of the
high-productivity belt and reduced winter sea-ice
(Niirnberg 1995). Residual concentrations of organic carbon and extensive lateral advection of
material (opal) impede the comparison of productivity proxies here.
At the Antarctic continental margin, productivity increased drastically in the Holocene and peak
warm-stages, reaching values representative of
recent upwelling areas in stage 5.5 (Bonn et al.
1998). In glacial stages, productivity ceased almost
completely due to a permanent sea-ice coverage.
Downcore distributions of organic carbon are rather
featureless in these cores, whereas the opal contents correlate well with concentrations of biogenic
barium (Bonn et al. 1998). However, amplitudes of
opal concentrations decrease with age and the oldest barium peak (stage 11) is no longer matched
by an opal peak in core PS 1821-6.
Summarizing the comparison of proxies from
our selection of cores, it can be said that P calculations, using Ba(b;o) concentrations, ar~wconfirmed by other paleoproductivity proxies. Nevertheless, only biogenic barium can be applied to all
our cores, whereas the other proxies are subject
to limitations by latitude or sedimentary environment.
The comparison ofPn,w from core-top samples
computed according to Francois et al. (1995) with
maps of recent export production (Berger et al.
1989), or with calculations from TOC-accumulation (Bickert 1992), do not show unequivocal results. At the Equatorial Divergence, Pnew computed
according to Francois et al. (1995) is below estimations of recent export production (Berger et al.
1989), whereas Pnew values based on the calculations of Dymond et al. (1992) match recent values
and calculations derived from TOC-accumulation
(Gingele and Dahmke 1994). Holocene Pn,w values calculated from Ba-data in subantarctic waters (Niirnberg 1995) coincide with estimations of
recent export production (Wefer and Fischer 1991 ;
Treguer and van Bennekom 1991). At the Antarctic continental margin, estimations of recent export
production are rare and vary strongly due to strong
seasonality-spiked bloom events which dominate
the production. P ocw calculated from core top samples (5-50 g C m· 2 a·') exceeds values estimated
by Wefer and Fischer (1991) and Treguer and van
Bennekom (1991) near the Antarctic coast (0.5-5
g C m· 2 a· '). However, estimations based on data
from the Lazarev Sea (Gleitz et al. 1994) suggest
15-75 g C m· 2 a· 1 produced in a six-month period
(Bonn 1995). Average interglacial Pn,w values for
cores near the Antarctic coast range from 10-40 g
C m- 2 a-I (Bonn 1995). Generally, the approach of
Francois et al. (1995) yields 30-40% lower values
in peak warm stages as compared to the approach
of Dymond et al. (1992). The lack of sufficient data