472
Andersen et al.
In order to calibrate the sedimentary alkenone
3 13 C signal, the isotopic composition of this compound was measured in core-top samples from the
South Atlantic and compared to surface water
[C0 2 (aq)]p"_' nd and phosphate concentration. From
these data, a variable (b), reflecting intracellular
carbon demand and defining the correlation
between Ep and [CO/aq)], can be calculated
(see defin itions and calculations). We test ifthe variable b is correlatable with ambient concentrations
of seawater phosphate and dependent on growth
rate. Such a relationship was reported by Bidigare
et al. (1997) for alkenone 3 13 C signals of suspended particulate matter in modern oceans. We
also test if bulk sediment3 l S N, known to be a proxy
for the nutrient utilization (Altabet and Franyois
1994; Holmes et al. 1996, 1998; Holmes et al. this
10· N
10·
30·
50·S
volume), can be used for estimates of ancient
b-values.
The eastern Angola Basin is a region of high
primary productivity (e.g. Berger et al. 1989)
due to a shallow thermocline (20-25 m) and the
occurrence of oceanic upwelling (van Bennekom
and Berger 1984; Ravelo et al. 1990). Therefore,
our core GeoB 1016-3 is suitable for testing the
effect of high biological productivity to atmospheric
pC0 2 at low latitudes. Productivity, particularly
in low-latitude upwelling regions, was probably
higher during the glacial periods than at present in
both the Atlantic Ocean (MUlier and Suess 1979;
MUlier et al. 1983 ; Samthein et al. 1988; Lyle 1988;
Mix 1989; Schneider et al. 1994) and the Pacific
Ocean (Finney et al. 1988; Lyle 1988; Thunell et
al. 1992).
SO· W
40·
20·
Longitude
O·
Fig. 1. Map of the study area in the South Atlantic showing the positions of the GeoB surface sediments. Arrows
indicate surface current system: NBC -North Brazil Current, NEC -North Equatorial Current, NECC - North Equatorial Counter Current, SEC - South Equatorial Current, SECC - South Equatorial Counter Current, GC - Guinea
Current, AC - Angola Current, BCC - Benguela Coastal Current, BOC - Benguela Oceanic Current, SAC - South
Atlantic Current, BC - Brazil Current.
Andersen et al.
In order to calibrate the sedimentary alkenone
3 13 C signal, the isotopic composition of this compound was measured in core-top samples from the
South Atlantic and compared to surface water
[C0 2 (aq)]p"_' nd and phosphate concentration. From
these data, a variable (b), reflecting intracellular
carbon demand and defining the correlation
between Ep and [CO/aq)], can be calculated
(see defin itions and calculations). We test ifthe variable b is correlatable with ambient concentrations
of seawater phosphate and dependent on growth
rate. Such a relationship was reported by Bidigare
et al. (1997) for alkenone 3 13 C signals of suspended particulate matter in modern oceans. We
also test if bulk sediment3 l S N, known to be a proxy
for the nutrient utilization (Altabet and Franyois
1994; Holmes et al. 1996, 1998; Holmes et al. this
10· N
10·
30·
50·S
volume), can be used for estimates of ancient
b-values.
The eastern Angola Basin is a region of high
primary productivity (e.g. Berger et al. 1989)
due to a shallow thermocline (20-25 m) and the
occurrence of oceanic upwelling (van Bennekom
and Berger 1984; Ravelo et al. 1990). Therefore,
our core GeoB 1016-3 is suitable for testing the
effect of high biological productivity to atmospheric
pC0 2 at low latitudes. Productivity, particularly
in low-latitude upwelling regions, was probably
higher during the glacial periods than at present in
both the Atlantic Ocean (MUlier and Suess 1979;
MUlier et al. 1983 ; Samthein et al. 1988; Lyle 1988;
Mix 1989; Schneider et al. 1994) and the Pacific
Ocean (Finney et al. 1988; Lyle 1988; Thunell et
al. 1992).
SO· W
40·
20·
Longitude
O·
Fig. 1. Map of the study area in the South Atlantic showing the positions of the GeoB surface sediments. Arrows
indicate surface current system: NBC -North Brazil Current, NEC -North Equatorial Current, NECC - North Equatorial Counter Current, SEC - South Equatorial Current, SECC - South Equatorial Counter Current, GC - Guinea
Current, AC - Angola Current, BCC - Benguela Coastal Current, BOC - Benguela Oceanic Current, SAC - South
Atlantic Current, BC - Brazil Current.