Carbonate Dissolution in the Deep-Sea
261
decrease in the course of dissolution in some
planktic foraminiferal species (Bender et al. 1975;
Rosenthal and Boyle 1993; Hastings 1994; Russell
et al. 1994; Niirnberg 1995). The reason is that
chambers, keel and "cortex" are each secreted in
different depths displaying a distinct chemical water composition, and dissolution removes the most
"impure" calcite parts first and faster than pure
calcite (Brown and Elderfield 1996). As the
foraminiferal assemblage is changed qualitatively
and quantitatively due to dissolution, the perturbation of the record makes the interpretation difficult,
and some method must be found to indicate the
extent of bias caused by dissolution (Hemleben et
al. 1989).
There are routinely measured micropaleontological and sedimentological methods considered to be linked to carbonate dissolution and
preservation. These methods include determination
of (1) percentage of fragmented planktic
foraminifera tests (e.g. Keigwin 1976; Le and
Shackleton 1992); (2) proportions of solution susceptible and solution resistant planktic foraminifera
species (e.g. Schott 1935; Berger 1979; Boltovskoy
and Totah 1992); (3) the ratio of benthic to planktic
foraminifera (e.g. Parker and Berger 1971; Hooper
et al. 1991); (4) the ratio ofagglutinating to calcifying foraminifera (e.g. Kennett 1966; Murray
1989): (5) the ratio of radiolaria to foraminifera
(Peterson and Prell 1985); (6) the ratio of pteropods
to foraminifera (Berner 1977); (7) the ratio of
coccoliths to foraminifera (e.g. Hay 1970; Hsii and
Andrews 1970). Each of these parameters is a
potential dissolution index, but their variations may
partly be controlled by ecological or other factors
(e.g. productivity, winnowing). Thus mostly, a multimethod approach was used in carbonate dissolution-studies.
Several similar rankings of the solubility of
planktic foraminifera (Table 1) were derived from
sediment samples, from taut wire buoys, from
mooring experiments, and from laboratory experiments. This ranking depends on chamber structure,
test size, thickness of the shell, development of a
"cortex", dimension of aperture, existence of
spines, width of pores, fragility of sutures (Berger
1979; Henrich and Wefer 1986). It is stated that
Globigerinoides ruber is one of the most solutionsusceptible species whereas Neogloboquadrina
sp. belongs to the rather solution-resistant species.
According to Berger (l973b), benthic
foraminifera are approximately three times less
susceptible to dissolution than planktic foraminifera.
Unfortunately, the information available on the dissolution of benthic foraminifera is scarce and fragmentary. Corliss and Honjo (1981) compiled a table of the relative susceptibility of benthic
foraminifera to dissolution. It should be noted that
at least some planktic foraminifera are more resistant than certain benthic ones (Adelseck 1977;
Boltovskoy and Totah 1992).
Another method is based on the ratio of the
number of insoluble organic linings of five benthic
foraminifera species to the number of calcareous
shells ofthe same species (De Vernal et al. 1992).
Maximum concentrations of organic linings correspond with a minimum of well-preserved shells and
vice versa. The known relation between calcareous shells and their organic linings may lead to a
dissolution index.
Dissolution of Calcareous Nannoplankton
assemblages
Due to their small size, delicate ultrastructure, and
complex sedimentation processes, relatively little
work was done on coccolith dissolution as compared
to planktic foraminifera. An early attempt to establish a preservation index was made by Roth and
Thierstein (1972) who set up four categories of
etching to express the preservation state of a
coccolith assemblage. Among others, Hay (1970)
stated that coccoliths show the best resistance to
dissolution in deep waters especially compared with
planktic foraminifera and other carbonate secreting invertebrates. He found - confirmed by early
results of the Deep Sea Drilling Project - coccoliths
to be more abundant close to the CCD than
foraminifera. However, the results of Berger
(1973b), Roth and Coulbourn (1982), and Paull et
al. (1988) suggest that the dissolution behavior of
coccoliths and foraminifera is rather similar, although differences in range of resistance cannot
be 'excluded.
The occurrence of well-preserved coccoliths
far below the CCD was then explained by protec-
261
decrease in the course of dissolution in some
planktic foraminiferal species (Bender et al. 1975;
Rosenthal and Boyle 1993; Hastings 1994; Russell
et al. 1994; Niirnberg 1995). The reason is that
chambers, keel and "cortex" are each secreted in
different depths displaying a distinct chemical water composition, and dissolution removes the most
"impure" calcite parts first and faster than pure
calcite (Brown and Elderfield 1996). As the
foraminiferal assemblage is changed qualitatively
and quantitatively due to dissolution, the perturbation of the record makes the interpretation difficult,
and some method must be found to indicate the
extent of bias caused by dissolution (Hemleben et
al. 1989).
There are routinely measured micropaleontological and sedimentological methods considered to be linked to carbonate dissolution and
preservation. These methods include determination
of (1) percentage of fragmented planktic
foraminifera tests (e.g. Keigwin 1976; Le and
Shackleton 1992); (2) proportions of solution susceptible and solution resistant planktic foraminifera
species (e.g. Schott 1935; Berger 1979; Boltovskoy
and Totah 1992); (3) the ratio of benthic to planktic
foraminifera (e.g. Parker and Berger 1971; Hooper
et al. 1991); (4) the ratio ofagglutinating to calcifying foraminifera (e.g. Kennett 1966; Murray
1989): (5) the ratio of radiolaria to foraminifera
(Peterson and Prell 1985); (6) the ratio of pteropods
to foraminifera (Berner 1977); (7) the ratio of
coccoliths to foraminifera (e.g. Hay 1970; Hsii and
Andrews 1970). Each of these parameters is a
potential dissolution index, but their variations may
partly be controlled by ecological or other factors
(e.g. productivity, winnowing). Thus mostly, a multimethod approach was used in carbonate dissolution-studies.
Several similar rankings of the solubility of
planktic foraminifera (Table 1) were derived from
sediment samples, from taut wire buoys, from
mooring experiments, and from laboratory experiments. This ranking depends on chamber structure,
test size, thickness of the shell, development of a
"cortex", dimension of aperture, existence of
spines, width of pores, fragility of sutures (Berger
1979; Henrich and Wefer 1986). It is stated that
Globigerinoides ruber is one of the most solutionsusceptible species whereas Neogloboquadrina
sp. belongs to the rather solution-resistant species.
According to Berger (l973b), benthic
foraminifera are approximately three times less
susceptible to dissolution than planktic foraminifera.
Unfortunately, the information available on the dissolution of benthic foraminifera is scarce and fragmentary. Corliss and Honjo (1981) compiled a table of the relative susceptibility of benthic
foraminifera to dissolution. It should be noted that
at least some planktic foraminifera are more resistant than certain benthic ones (Adelseck 1977;
Boltovskoy and Totah 1992).
Another method is based on the ratio of the
number of insoluble organic linings of five benthic
foraminifera species to the number of calcareous
shells ofthe same species (De Vernal et al. 1992).
Maximum concentrations of organic linings correspond with a minimum of well-preserved shells and
vice versa. The known relation between calcareous shells and their organic linings may lead to a
dissolution index.
Dissolution of Calcareous Nannoplankton
assemblages
Due to their small size, delicate ultrastructure, and
complex sedimentation processes, relatively little
work was done on coccolith dissolution as compared
to planktic foraminifera. An early attempt to establish a preservation index was made by Roth and
Thierstein (1972) who set up four categories of
etching to express the preservation state of a
coccolith assemblage. Among others, Hay (1970)
stated that coccoliths show the best resistance to
dissolution in deep waters especially compared with
planktic foraminifera and other carbonate secreting invertebrates. He found - confirmed by early
results of the Deep Sea Drilling Project - coccoliths
to be more abundant close to the CCD than
foraminifera. However, the results of Berger
(1973b), Roth and Coulbourn (1982), and Paull et
al. (1988) suggest that the dissolution behavior of
coccoliths and foraminifera is rather similar, although differences in range of resistance cannot
be 'excluded.
The occurrence of well-preserved coccoliths
far below the CCD was then explained by protec-