256
Dittert et al.
paleontology, changes in faunal composition recorded in pelagic sequences could be explained to
be dependent on both changes in the composition
ofthe living assemblages and in the intensity of dissolution and resulting fragmentation of the tests
(Schott 1935). Even before this, Philippi (1910) already had established the hypothesis of increased
activity of Antarctic Bottom Water during glacials
based on an enhanced carbonate dissolution. However, one obstacle in recognizing that carbonate
dissolution in the eastern tropical Pacific was in fact
less important during glacials than during
interglacials was the (mistaken) notion of
Globigerina sp. as being highly resistant to dissolution and of Globorotalia sp. as being highly susceptible to it (Arrhenius 1952). The reverse has
been shown to be correct (Berger 1967). In contrast to the situation in the equatorial Pacific,
Olausson (1965) showed that interglacials can be
assigned to high-carbonate stages and glacials to
low-carbonate stages in the Atlantic. The first demonstration that the long-term exposure of calcite
crystals to sea water on deep-sea moorings revealed
information on the depth dependence of dissolution
rate and calcite saturation was given by Peterson
(1966). Milliman (1975) repeated Peterson's experiment in the North Atlantic using aragonite, low and
high Mg calcite and confirmed that each of these
carbonate varieties had its own lysocline occurrence at critical levels of undersaturation. Berger
(1967, 1968) ranked planktic foraminifera species
collected from sediment samples according to dissolution resistance as a basis for forming dissolution indices. Furthermore, he exposed samples
which were derived from sediment and from plankton tows on a taut wire buoy (same mooring as that
used by Peterson 1966) at different depths in the
central Pacific, in order to assess the effects of
dissolution on foraminiferal shells. Additional information on the dissolution of planktic organisms were
delivered by investigations on coccolithophores
(Hay 1970) as well as on ptcropods (Berner 1977).
Comparison oflaboratory experiments with surface
sediment samples indicated differential preservation of coccolithophore species in oceanic
sediments (McIntyre and McIntyre 1971). Further
evidence of differential dissolution among shells
from analyses of living specimens and fossil shells
has been obtained by in-situ experiments using sediment traps (Honjo and Erez 1978) and by laboratory experiments (Be et al. 1975); comparisons
between water column communities and sediment
assemblages (including in-situ investigations) were
performed by Vilks (1975). With technological
progress and the invention of scanning electron
microscopy, Be et al. (1975) started investigations
of foraminiferal ultrastructure reaction to carbonate dissolution. They elaborated various speciesspecific SEM dissolution indices. This approach has
been
evaluated
for
Neogloboquadrina
pachyderma (Henrich 1989; Baumann and
Meggers 1996) and for Globigerina bulloides
(Van Kreveld 1996; Dittert and Henrich subm). For
both species the progressive ultrastructural breakdown with increasing dissolution could be shown.
In order to outline the essentials for carbonate dissolution in the deep-sea, a brief review on the carbon dioxide system and on the deep-water circulation in the world oceans will be presented. Many
different methodical approaches were established
as dissolution proxies in the past. We will contemplate the most important ones regarding the use of
bulk sediment parameters and the use of calcareous micro- and nannoplankton. Since the history of
"Carbonate dissolution in the deep-sea" covers
more than one hundred years, only a few scientists
who improved the comprehension ofthat complex
topic can be mentioned. An excellent summary on
previous studies is given by Boltovskoy (1991). This
leads up to the South Atlantic Dissolution Experiment, where the mentioned parameters are tested
for their usefulness at three surface sediment
transects into the Brazil Basin and through the Cape
Basin. At last, we will elucidate the advantages and
disadvantages of several dissolution proxies.
Some Aspects on the Carbon Dioxide
System and Carbonate Dissolution
The carbon dioxide flux between atmosphere and
ocean surface water is governed by molecular diffusion. Thereby the direction and magnitude of the
CO 2 flux depend on the gas exchange coefficient
of carbon, the thickness of the surface water
boundary layer, the solubility coefficient, and the
partial pressure difference between sea water and
Dittert et al.
paleontology, changes in faunal composition recorded in pelagic sequences could be explained to
be dependent on both changes in the composition
ofthe living assemblages and in the intensity of dissolution and resulting fragmentation of the tests
(Schott 1935). Even before this, Philippi (1910) already had established the hypothesis of increased
activity of Antarctic Bottom Water during glacials
based on an enhanced carbonate dissolution. However, one obstacle in recognizing that carbonate
dissolution in the eastern tropical Pacific was in fact
less important during glacials than during
interglacials was the (mistaken) notion of
Globigerina sp. as being highly resistant to dissolution and of Globorotalia sp. as being highly susceptible to it (Arrhenius 1952). The reverse has
been shown to be correct (Berger 1967). In contrast to the situation in the equatorial Pacific,
Olausson (1965) showed that interglacials can be
assigned to high-carbonate stages and glacials to
low-carbonate stages in the Atlantic. The first demonstration that the long-term exposure of calcite
crystals to sea water on deep-sea moorings revealed
information on the depth dependence of dissolution
rate and calcite saturation was given by Peterson
(1966). Milliman (1975) repeated Peterson's experiment in the North Atlantic using aragonite, low and
high Mg calcite and confirmed that each of these
carbonate varieties had its own lysocline occurrence at critical levels of undersaturation. Berger
(1967, 1968) ranked planktic foraminifera species
collected from sediment samples according to dissolution resistance as a basis for forming dissolution indices. Furthermore, he exposed samples
which were derived from sediment and from plankton tows on a taut wire buoy (same mooring as that
used by Peterson 1966) at different depths in the
central Pacific, in order to assess the effects of
dissolution on foraminiferal shells. Additional information on the dissolution of planktic organisms were
delivered by investigations on coccolithophores
(Hay 1970) as well as on ptcropods (Berner 1977).
Comparison oflaboratory experiments with surface
sediment samples indicated differential preservation of coccolithophore species in oceanic
sediments (McIntyre and McIntyre 1971). Further
evidence of differential dissolution among shells
from analyses of living specimens and fossil shells
has been obtained by in-situ experiments using sediment traps (Honjo and Erez 1978) and by laboratory experiments (Be et al. 1975); comparisons
between water column communities and sediment
assemblages (including in-situ investigations) were
performed by Vilks (1975). With technological
progress and the invention of scanning electron
microscopy, Be et al. (1975) started investigations
of foraminiferal ultrastructure reaction to carbonate dissolution. They elaborated various speciesspecific SEM dissolution indices. This approach has
been
evaluated
for
Neogloboquadrina
pachyderma (Henrich 1989; Baumann and
Meggers 1996) and for Globigerina bulloides
(Van Kreveld 1996; Dittert and Henrich subm). For
both species the progressive ultrastructural breakdown with increasing dissolution could be shown.
In order to outline the essentials for carbonate dissolution in the deep-sea, a brief review on the carbon dioxide system and on the deep-water circulation in the world oceans will be presented. Many
different methodical approaches were established
as dissolution proxies in the past. We will contemplate the most important ones regarding the use of
bulk sediment parameters and the use of calcareous micro- and nannoplankton. Since the history of
"Carbonate dissolution in the deep-sea" covers
more than one hundred years, only a few scientists
who improved the comprehension ofthat complex
topic can be mentioned. An excellent summary on
previous studies is given by Boltovskoy (1991). This
leads up to the South Atlantic Dissolution Experiment, where the mentioned parameters are tested
for their usefulness at three surface sediment
transects into the Brazil Basin and through the Cape
Basin. At last, we will elucidate the advantages and
disadvantages of several dissolution proxies.
Some Aspects on the Carbon Dioxide
System and Carbonate Dissolution
The carbon dioxide flux between atmosphere and
ocean surface water is governed by molecular diffusion. Thereby the direction and magnitude of the
CO 2 flux depend on the gas exchange coefficient
of carbon, the thickness of the surface water
boundary layer, the solubility coefficient, and the
partial pressure difference between sea water and