Carbonate Dissolution in the Deep-Sea
271
bottom of the sediment calcite transition zone is
considered to be located at about 5,000 m water
depth which corresponds to -30 !lmoVkg L1COt.
Because there are no values below -30 !lmol/kg
L1COt, this estimation is somewhat uncertain (Fig.
8a, b, right side). We should note, that GEOSECS
station 103 possibly belongs to the pelagic ocean
rather than to the continental margin and consequently C0 3 2- values may bias our results to some
extent.
With respect to transect 1, the grain size fraction 63 !lm - 150!lm increases from 15 % at 2,921
m to 70 % at 5,213 m water depth, the fractions
150 !lm - 355 !lm remain mostly unchanged, and
the fractions >355 !lm decrease from 60 % to about
10 %. In transect 2 as well as in transect 3, size
fractions do not vary greatly. Fluctuations amount
to 10 % maximum (Fig. 9, upper).
Dry bulk density decreases from 0.6 glcm 3 to
0.2 glcm 3 (transect 1) and from 0.9 g/cm 3 to OJ gI
cm 3 (transect 2). Only in transect 3 could a significant increase be detected. Values rise from 0.4 gI
cm 3 to 0.8 glcm 3 (Fig. 9, upper).
The rain ratio increases from 0.002 to about 0.07
with a distinct shift at 4,779 m water depth (transect
1). In transect 2, modifications are not that sharp.
The shift occurs at about 4,089 m towards 0.01.
The most recognizable changes occur in transect
3, where the rain ratio decreases from 0.05 to about
0.002 building an interim maximum of 0.02 at 1,964
m water depth (Fig. 9 lower; Fig. 13c).
Planktic foraminifera parameters. The modification of organism assemblages can be expressed
by the number of radiolaria, benthic and planktic
foraminifera> 150 !lm per gram sediment (Fig. 10,
upper). Transect 1 is characterized by a strong decrease in planktic foraminifera from 15,000 down
to 4,000 tests; benthic foraminifera increase from
500 to 3,000 tests, and radiolaria increase from 150
to 360,000 tests per gram sediment. The most vigorous shift can be seen at about 3,977 m water
depth. A similar picture is given in transect 2.
Planktic foraminifera decrease from 14,000 to
4,500 tests, benthic foraminifera increase from 600
to 1,100 tests, and radiolaria increase from 100 to
about 4,000 tests per gram sediment. A totally different situation occurs in transect 3: Planktic
foraminifera increase from 17,000 to 45,000 tests,
benthic foraminifera decrease from 1,800 to 500
tests, and radiolaria drop from 600 to 200 tests per
gram sediment.
Looking at the modification of planktic foraminiferal assemblages, thick- and thin shelled varieties
can be related to each other (Fig. 10, lower). In
transect 1, thick-shelled planktic foraminifera
amount to 25 % at 2,921 m and increase to about
80 % at 5,213 m with an interim peak of95 % at
4,675 m water depth. In transect 2, the amount of
60 % thick-shelled varieties at 2,007 m rises to 85
% at 4,669 m water depth. A similar picture appears
in transect 3 where 25 % thick-shelled tests at 1,007
m increase to 40 % at 3,837 m water depth.
The ratio of dissolution susceptible to resistant
planktic foraminifera shows a consistent trend in
all three transects. Values remain consistently low
from 1,007 m to 4,089 m, shift from about 0.2 to
0.6 and 0.8 at 4,670 m and drop then to 0.6 at 5,213
m water depth (Figs. lla,t). The ratio of radiolaria
to planktic foraminifera starts with about zero at
1,007 m and shifts at 4,089 m to about 1 at 5,213 m
water depth (Fig. 11 c). In a similar manner, the ratio
of benthic to planktic foraminifera begins with
about zero at 1,007 mandjumps at4,089m to about
0.5 at 5,213 m water depth (Fig. lId). The
foraminiferal dissolution index (FDX) commences
at about 4.5 at 1,007 mrises at 4,089 m to 7 at 4,675
m and decreases to about 6 at 5,213 m water depth
with respect to transects I and 3. Transect 2 starts
on a higher level with 6 at 2,007 m and increases
with a low slope to about 7 at 4,669 m water depth
(Fig. 11 b). Likewise, the fragmentation index of the
sum of planktic foraminifera remains mostly unchanged from 1,007 m to 3,977 m and then shifts
from 0.3 to 0.8 at 4,675 m, then decreasing to 0.4
at 5,213 m water depth according to transects 1
and 3. Values of transect 2 increase from 0.2 at
2,007 m to 0.8 at 4,089 m, then drop to 0.2 at 4,700
m water depth (Fig. lie). Looking at the fragmentation of Globigerina sacculifer tests, the values
of all transects slightly increase from about zero at
2,007 m to 0.9 at 4,089 m. Transect 2 values drop
to 0.1 at 4,669 m whereas transect 1 values rise to
0.9 at 4,675 m and then drop to OJ at 5,213 m water
depth (Fig. Ilg).
271
bottom of the sediment calcite transition zone is
considered to be located at about 5,000 m water
depth which corresponds to -30 !lmoVkg L1COt.
Because there are no values below -30 !lmol/kg
L1COt, this estimation is somewhat uncertain (Fig.
8a, b, right side). We should note, that GEOSECS
station 103 possibly belongs to the pelagic ocean
rather than to the continental margin and consequently C0 3 2- values may bias our results to some
extent.
With respect to transect 1, the grain size fraction 63 !lm - 150!lm increases from 15 % at 2,921
m to 70 % at 5,213 m water depth, the fractions
150 !lm - 355 !lm remain mostly unchanged, and
the fractions >355 !lm decrease from 60 % to about
10 %. In transect 2 as well as in transect 3, size
fractions do not vary greatly. Fluctuations amount
to 10 % maximum (Fig. 9, upper).
Dry bulk density decreases from 0.6 glcm 3 to
0.2 glcm 3 (transect 1) and from 0.9 g/cm 3 to OJ gI
cm 3 (transect 2). Only in transect 3 could a significant increase be detected. Values rise from 0.4 gI
cm 3 to 0.8 glcm 3 (Fig. 9, upper).
The rain ratio increases from 0.002 to about 0.07
with a distinct shift at 4,779 m water depth (transect
1). In transect 2, modifications are not that sharp.
The shift occurs at about 4,089 m towards 0.01.
The most recognizable changes occur in transect
3, where the rain ratio decreases from 0.05 to about
0.002 building an interim maximum of 0.02 at 1,964
m water depth (Fig. 9 lower; Fig. 13c).
Planktic foraminifera parameters. The modification of organism assemblages can be expressed
by the number of radiolaria, benthic and planktic
foraminifera> 150 !lm per gram sediment (Fig. 10,
upper). Transect 1 is characterized by a strong decrease in planktic foraminifera from 15,000 down
to 4,000 tests; benthic foraminifera increase from
500 to 3,000 tests, and radiolaria increase from 150
to 360,000 tests per gram sediment. The most vigorous shift can be seen at about 3,977 m water
depth. A similar picture is given in transect 2.
Planktic foraminifera decrease from 14,000 to
4,500 tests, benthic foraminifera increase from 600
to 1,100 tests, and radiolaria increase from 100 to
about 4,000 tests per gram sediment. A totally different situation occurs in transect 3: Planktic
foraminifera increase from 17,000 to 45,000 tests,
benthic foraminifera decrease from 1,800 to 500
tests, and radiolaria drop from 600 to 200 tests per
gram sediment.
Looking at the modification of planktic foraminiferal assemblages, thick- and thin shelled varieties
can be related to each other (Fig. 10, lower). In
transect 1, thick-shelled planktic foraminifera
amount to 25 % at 2,921 m and increase to about
80 % at 5,213 m with an interim peak of95 % at
4,675 m water depth. In transect 2, the amount of
60 % thick-shelled varieties at 2,007 m rises to 85
% at 4,669 m water depth. A similar picture appears
in transect 3 where 25 % thick-shelled tests at 1,007
m increase to 40 % at 3,837 m water depth.
The ratio of dissolution susceptible to resistant
planktic foraminifera shows a consistent trend in
all three transects. Values remain consistently low
from 1,007 m to 4,089 m, shift from about 0.2 to
0.6 and 0.8 at 4,670 m and drop then to 0.6 at 5,213
m water depth (Figs. lla,t). The ratio of radiolaria
to planktic foraminifera starts with about zero at
1,007 m and shifts at 4,089 m to about 1 at 5,213 m
water depth (Fig. 11 c). In a similar manner, the ratio
of benthic to planktic foraminifera begins with
about zero at 1,007 mandjumps at4,089m to about
0.5 at 5,213 m water depth (Fig. lId). The
foraminiferal dissolution index (FDX) commences
at about 4.5 at 1,007 mrises at 4,089 m to 7 at 4,675
m and decreases to about 6 at 5,213 m water depth
with respect to transects I and 3. Transect 2 starts
on a higher level with 6 at 2,007 m and increases
with a low slope to about 7 at 4,669 m water depth
(Fig. 11 b). Likewise, the fragmentation index of the
sum of planktic foraminifera remains mostly unchanged from 1,007 m to 3,977 m and then shifts
from 0.3 to 0.8 at 4,675 m, then decreasing to 0.4
at 5,213 m water depth according to transects 1
and 3. Values of transect 2 increase from 0.2 at
2,007 m to 0.8 at 4,089 m, then drop to 0.2 at 4,700
m water depth (Fig. lie). Looking at the fragmentation of Globigerina sacculifer tests, the values
of all transects slightly increase from about zero at
2,007 m to 0.9 at 4,089 m. Transect 2 values drop
to 0.1 at 4,669 m whereas transect 1 values rise to
0.9 at 4,675 m and then drop to OJ at 5,213 m water
depth (Fig. Ilg).