Clues to Ocean History: a Brief Overview of Proxies
13
applicable in the middle tropics and along the equator, where there is no chance oflateral invasion of
a front.
Isotopic studies of pteropods (Fischer et al. this
volume) can provide a much higher temporal resolution than can be achieved with foraminiferal tests
from the sediments (Kalberer et al. 1993). Some
shells are large enough that multiple samples can
be taken from a single individual. In addition, some
species are assumed to live for one entire year.
This would allow to reconstruct a year-long record
oftemperature and an annual mean value. Because
the isotopic composition of the water can be assumed to be constant, the oxygen-isotope variations
represent temperature fluctuations throughout the
year. As an example, the oxygen isotope variations
in the pteropodLimacina inflata sampled with sediment traps off Cape Blanc are shown in Fig. 6.
There is clear agreement between measured surface-near temperatures and those calculated from
isotopes.
-2.0 <) N. pachyderma (left)
0 G. sacculifer
... G. truncatulinoides (right)
T G. truncatulinoides (left)
0
0
[0 0.0
0
0..
l
0
<0
~
r.o
2.0
T
<)
4.0
60 0 S 50
40
30
Deep-sea corals provide an opportunity for
documenting rapid temperature changes at depth
(Mangini et al. 1998), especially for intermediate
waters (Smith et al. 1997). According to 14C ages,
the corals investigated by Mangini et al. (1998) lived
for less than 200 years and documented the first
deglacial meltwater spike (1 A) at a depth of2306 m
in the equatorial Atlantic. UITh ages show that the
age of the bottom water was perhaps 250 years
older than today, suggesting a slower water exchange than today. From 1) 18 0 values of a deepsea coral from a depth of 1600m in the northwestern Atlantic, Smith et al. (1997) were able to recognize deep-reaching changes in the intermediatewater circulation during the Younger Dryas. Because corals - and also pteropods - are made out
of aragonite, they provide much better 2l0ThJ2l4U
dates than other fossils (Bard et al. 1993), and a
comparison between 14C and u/Th ages allows an
estimation of the age of water masses and thereby
of ventilation and turnover rates.
30
E
UJ
a::
::J
20 ~
0
a::
UJ
a.
:;
UJ
fCi
UJ
10
(.!)
«
a::
UJ
> «
~
...J
0
« z
0
N
20
10
0
100N
LATITUDE
Fig. 5. Latitudinal distribution of oxygen isotope composition of N. pachyderma, G. sacculifer (white symbols),
and G. truncatulinoides (black symbols), and zonally (60 0 W-200E) and yearly averaged temperature at the sea
surface and at 250 m water depth (Levitus 1982). From Mulitza et al. (1997).
13
applicable in the middle tropics and along the equator, where there is no chance oflateral invasion of
a front.
Isotopic studies of pteropods (Fischer et al. this
volume) can provide a much higher temporal resolution than can be achieved with foraminiferal tests
from the sediments (Kalberer et al. 1993). Some
shells are large enough that multiple samples can
be taken from a single individual. In addition, some
species are assumed to live for one entire year.
This would allow to reconstruct a year-long record
oftemperature and an annual mean value. Because
the isotopic composition of the water can be assumed to be constant, the oxygen-isotope variations
represent temperature fluctuations throughout the
year. As an example, the oxygen isotope variations
in the pteropodLimacina inflata sampled with sediment traps off Cape Blanc are shown in Fig. 6.
There is clear agreement between measured surface-near temperatures and those calculated from
isotopes.
-2.0 <) N. pachyderma (left)
0 G. sacculifer
... G. truncatulinoides (right)
T G. truncatulinoides (left)
0
0
[0 0.0
0
0..
l
0
<0
~
r.o
2.0
T
<)
4.0
60 0 S 50
40
30
Deep-sea corals provide an opportunity for
documenting rapid temperature changes at depth
(Mangini et al. 1998), especially for intermediate
waters (Smith et al. 1997). According to 14C ages,
the corals investigated by Mangini et al. (1998) lived
for less than 200 years and documented the first
deglacial meltwater spike (1 A) at a depth of2306 m
in the equatorial Atlantic. UITh ages show that the
age of the bottom water was perhaps 250 years
older than today, suggesting a slower water exchange than today. From 1) 18 0 values of a deepsea coral from a depth of 1600m in the northwestern Atlantic, Smith et al. (1997) were able to recognize deep-reaching changes in the intermediatewater circulation during the Younger Dryas. Because corals - and also pteropods - are made out
of aragonite, they provide much better 2l0ThJ2l4U
dates than other fossils (Bard et al. 1993), and a
comparison between 14C and u/Th ages allows an
estimation of the age of water masses and thereby
of ventilation and turnover rates.
30
E
UJ
a::
::J
20 ~
0
a::
UJ
a.
:;
UJ
fCi
UJ
10
(.!)
«
a::
UJ
> «
~
...J
0
« z
0
N
20
10
0
100N
LATITUDE
Fig. 5. Latitudinal distribution of oxygen isotope composition of N. pachyderma, G. sacculifer (white symbols),
and G. truncatulinoides (black symbols), and zonally (60 0 W-200E) and yearly averaged temperature at the sea
surface and at 250 m water depth (Levitus 1982). From Mulitza et al. (1997).