202
Fischer et al.
2.0
1988
I
1989
1990
I
I
I
1991
I
I
I
~~o~
I
CO
~
0
0..
1.0
I
!
:
i
0
;,R
I
•
~
()
•
C'?
I
~
..I
I
E!
I
(jj
) [\
0
"0
0
0.0
o G.r. shallow
I
• G.r. deep
1-Jan
1-Jul
1-Jan
1-Jul
1-Jan
1-Jul
1-Jan
1-Jul
1-Jan
Fig. 4. Seasonal I)I3C record of juvenile L. inflata and G. ruber. Note the difference in absolute numbers (much
higher values of L. iriflata) and in seasonal amplitude.
duced by G. ruber. Instead, a slight 8!3C increase
was observed.
F or a better comparison of the 8!3C records of
L. injlata and G. ruber, we corrected the 8!3C of
L. injlata for the temperature effect by applying
the equation of Grossman and Ku (1986) and the
8 18 °-temperatures. We then obtained a better
agreement between the two records (Figs. 4, 6a)
and both records generally show 8 13 C maxima in
summer and minima in winter and spring. However,
an offset in the range of 0.7%0 (mean difference)
between the two species remains. The observed
seasonal pattern can be partly explained by the photosynthetic uptake of light carbon in the upper
water column in summer, which follows intensive
coastal upwelling in spring ('2C enriched upwelled
waters) induced by the SE trade winds. One might
assume that pteropod-8!3C responds to changes in
the 8!3C LC0 2 more predictably than
foraminiferal-o!3C (e.g. Grossman et al. 1986;
Jasper and Deuser 1993), the latter species being
affected by metabolic processes and feeding strategies. This seems to be true for the summer-o!3C
maxima of L. injlata which agree better to the
organic carbon export fluxes at a depth of 100 m
(Fig. 6b; calculated after Martin et al. 1987), the
latter being largely responsible for changes in surface water olJC LC0 2 (Berger and Vincent
1986). In addition, the lower seasonal variability in
carbon fluxes in 1990 is better documented by the
pteropod-o!3C record. Concerning the absolute
numbers in 013C, L. injlata (mean: 1.14%0, lower
traps) also appears to produce more accurate numbers for ambient O!3C LC0 2 than G. ruber (mean:
0.41%0, lower traps). During the GEOSECS expedition (site 115; Kroopnick 1985),013C values of
1.0%0 were measured in March 1973 which match
the O!3C of L. injlata (temperature-corrected)
during that period oftime (Fig. 6a). Unpublished
O!3C LC0 2 values (G. Ganssen, Amsterdam),
measured in the central Atlantic in April, were even
higher and ranged from 1.3%0 to 1.6%0 in 50 m
Fischer et al.
2.0
1988
I
1989
1990
I
I
I
1991
I
I
I
~~o~
I
CO
~
0
0..
1.0
I
!
:
i
0
;,R
I
•
~
()
•
C'?
I
~
..I
I
E!
I
(jj
) [\
0
"0
0
0.0
o G.r. shallow
I
• G.r. deep
1-Jan
1-Jul
1-Jan
1-Jul
1-Jan
1-Jul
1-Jan
1-Jul
1-Jan
Fig. 4. Seasonal I)I3C record of juvenile L. inflata and G. ruber. Note the difference in absolute numbers (much
higher values of L. iriflata) and in seasonal amplitude.
duced by G. ruber. Instead, a slight 8!3C increase
was observed.
F or a better comparison of the 8!3C records of
L. injlata and G. ruber, we corrected the 8!3C of
L. injlata for the temperature effect by applying
the equation of Grossman and Ku (1986) and the
8 18 °-temperatures. We then obtained a better
agreement between the two records (Figs. 4, 6a)
and both records generally show 8 13 C maxima in
summer and minima in winter and spring. However,
an offset in the range of 0.7%0 (mean difference)
between the two species remains. The observed
seasonal pattern can be partly explained by the photosynthetic uptake of light carbon in the upper
water column in summer, which follows intensive
coastal upwelling in spring ('2C enriched upwelled
waters) induced by the SE trade winds. One might
assume that pteropod-8!3C responds to changes in
the 8!3C LC0 2 more predictably than
foraminiferal-o!3C (e.g. Grossman et al. 1986;
Jasper and Deuser 1993), the latter species being
affected by metabolic processes and feeding strategies. This seems to be true for the summer-o!3C
maxima of L. injlata which agree better to the
organic carbon export fluxes at a depth of 100 m
(Fig. 6b; calculated after Martin et al. 1987), the
latter being largely responsible for changes in surface water olJC LC0 2 (Berger and Vincent
1986). In addition, the lower seasonal variability in
carbon fluxes in 1990 is better documented by the
pteropod-o!3C record. Concerning the absolute
numbers in 013C, L. injlata (mean: 1.14%0, lower
traps) also appears to produce more accurate numbers for ambient O!3C LC0 2 than G. ruber (mean:
0.41%0, lower traps). During the GEOSECS expedition (site 115; Kroopnick 1985),013C values of
1.0%0 were measured in March 1973 which match
the O!3C of L. injlata (temperature-corrected)
during that period oftime (Fig. 6a). Unpublished
O!3C LC0 2 values (G. Ganssen, Amsterdam),
measured in the central Atlantic in April, were even
higher and ranged from 1.3%0 to 1.6%0 in 50 m