196
Fischer et al.
season-dependent values were derived from
Mittelstaedt (1991): 36.2%0 for spring, 35.9%0 for
summer and 36.4%0 for fall and winter. We used
an equilibrium offset of -0.35%0 for the algal symbiont-bearing spinose species G. ruber (Fairbanks
et al. 1980; Deuser and Ross 1989) and applied an
aragonite-calcite correction factor of 0.6%0
(Tarutani et al. 1969) for temperature calculations
from L. inflata.
Measured sea surface temperatures taken from
IGOSS (Integrated Global Ocean Services System) are weekly means on a one-degree grid using in-situ and satellite values (corrected after
Reynolds 1988). For 1988 and 1989, in-situ data
were obtained from COADS, after 1990 onwards,
radio messages carried on the Global Telecommunication System were used.
Regional Setting
The moorings were located in a western boundary
current, the cold Canary Current; this region is influenced by the northeastern trade winds and the
resulting upwelling of cold and nutrient-rich subsurface waters off northwest Africa. Fairly persistent and strong northeastern trades off Cape Blanc
lead to a more or less continuous upwelling throughout the year (Schemainda et al. 1975, Van Camp
et al. 1991). Stronger wind intensities occur mainly
during spring and from late summer to fall.
Phytoplankton biomass is high along the coast but
drops beyond the shelfbreak. However, the Cape
Blanc area is characterized by "giant filaments"
with chlorophyll concentrations above 1 mg m· 3 •
These filaments have been observed several hundred kilometers offshore (Van Camp et al. 1991)
and vary seasonally and interannually. A detailed
description ofthe study site is given by Fischer et
al. (1996). Currents were measured in the vicinity
of the traps and revealed generally lower values
«10 cm S·I). Near the deeper traps, located in the
southward flowing NADW (North Atlantic Deep
Water), current velocities were lower than in
the upper water column merely ranging from 0 to
8 cm S·1 only.
Results and Discussion
Oxygen Isotopes, Seasonal and Interannual
Temperature Variations
The seasonal variations in the oxygen isotope composition of L. inflata(juveniles=250 11m, and adults
(> Imm) for 1989 only) andG. ruber(200-300 11m)
are shown in Fig. la and Table 1. As expected,
values derived from the upper and lower trap samples of both species are almost similar. The seasonal patterns of both species show highest values
in winter and spring and lower values in late summer and fall. However, absolute values vary significantly, displaying a difference of almost 2%0 in
September, 1988, to less than 0.5%0 in June, 1989.
Surprisingly, the oxygen isotope record of adultL.
inflata (> 1 mm) also produces a seasonal signal,
although studies conducted by Van der Spoel (1973)
and Wells (1976) revealed that these organisms
have a longevity of up to one year. Our seasonal
isotope record of adult L. inflata, however, suggests rapid growth and relatively short life spans
of these specimens in the range of several weeks
to a few months. This is consistent with the findings of Jasper and Deuser (1993).
The species fluxes of G. ruber (w) (fraction
>150 11m; Fig. Ib; Table 1) show highest values
during periods oflower oxygen isotope values occurring from late summer to fall (Fig. la), hence
during the warm season. This observation corresponds to findings derived from laboratory experiments which show that the growth ofG. ruber is
at least partly controlled by temperature (e.g. Bijma
et al. 1990). The calculated seasonal water temperatures and the annual means are given in Fig.
lc; L. inflata produces ambient water temperatures mostly lower than those derived from G.
ruber (white). The latter is thought to be a good
estimator for SSTs (Ravelo and Fairbanks 1992)
because of its occurrence throughout the year
(Deuser et al. 1981); th is species is assumed to
calcify in the mixed layer (around 0-25 m (Deuser
1987), in the upper 50 m (Kemle-v. MUcke 1994)
or in the range from 0 to 80 m (Ravelo and
Fischer et al.
season-dependent values were derived from
Mittelstaedt (1991): 36.2%0 for spring, 35.9%0 for
summer and 36.4%0 for fall and winter. We used
an equilibrium offset of -0.35%0 for the algal symbiont-bearing spinose species G. ruber (Fairbanks
et al. 1980; Deuser and Ross 1989) and applied an
aragonite-calcite correction factor of 0.6%0
(Tarutani et al. 1969) for temperature calculations
from L. inflata.
Measured sea surface temperatures taken from
IGOSS (Integrated Global Ocean Services System) are weekly means on a one-degree grid using in-situ and satellite values (corrected after
Reynolds 1988). For 1988 and 1989, in-situ data
were obtained from COADS, after 1990 onwards,
radio messages carried on the Global Telecommunication System were used.
Regional Setting
The moorings were located in a western boundary
current, the cold Canary Current; this region is influenced by the northeastern trade winds and the
resulting upwelling of cold and nutrient-rich subsurface waters off northwest Africa. Fairly persistent and strong northeastern trades off Cape Blanc
lead to a more or less continuous upwelling throughout the year (Schemainda et al. 1975, Van Camp
et al. 1991). Stronger wind intensities occur mainly
during spring and from late summer to fall.
Phytoplankton biomass is high along the coast but
drops beyond the shelfbreak. However, the Cape
Blanc area is characterized by "giant filaments"
with chlorophyll concentrations above 1 mg m· 3 •
These filaments have been observed several hundred kilometers offshore (Van Camp et al. 1991)
and vary seasonally and interannually. A detailed
description ofthe study site is given by Fischer et
al. (1996). Currents were measured in the vicinity
of the traps and revealed generally lower values
«10 cm S·I). Near the deeper traps, located in the
southward flowing NADW (North Atlantic Deep
Water), current velocities were lower than in
the upper water column merely ranging from 0 to
8 cm S·1 only.
Results and Discussion
Oxygen Isotopes, Seasonal and Interannual
Temperature Variations
The seasonal variations in the oxygen isotope composition of L. inflata(juveniles=250 11m, and adults
(> Imm) for 1989 only) andG. ruber(200-300 11m)
are shown in Fig. la and Table 1. As expected,
values derived from the upper and lower trap samples of both species are almost similar. The seasonal patterns of both species show highest values
in winter and spring and lower values in late summer and fall. However, absolute values vary significantly, displaying a difference of almost 2%0 in
September, 1988, to less than 0.5%0 in June, 1989.
Surprisingly, the oxygen isotope record of adultL.
inflata (> 1 mm) also produces a seasonal signal,
although studies conducted by Van der Spoel (1973)
and Wells (1976) revealed that these organisms
have a longevity of up to one year. Our seasonal
isotope record of adult L. inflata, however, suggests rapid growth and relatively short life spans
of these specimens in the range of several weeks
to a few months. This is consistent with the findings of Jasper and Deuser (1993).
The species fluxes of G. ruber (w) (fraction
>150 11m; Fig. Ib; Table 1) show highest values
during periods oflower oxygen isotope values occurring from late summer to fall (Fig. la), hence
during the warm season. This observation corresponds to findings derived from laboratory experiments which show that the growth ofG. ruber is
at least partly controlled by temperature (e.g. Bijma
et al. 1990). The calculated seasonal water temperatures and the annual means are given in Fig.
lc; L. inflata produces ambient water temperatures mostly lower than those derived from G.
ruber (white). The latter is thought to be a good
estimator for SSTs (Ravelo and Fairbanks 1992)
because of its occurrence throughout the year
(Deuser et al. 1981); th is species is assumed to
calcify in the mixed layer (around 0-25 m (Deuser
1987), in the upper 50 m (Kemle-v. MUcke 1994)
or in the range from 0 to 80 m (Ravelo and