Carbonate Dissolution in the Deep-Sea
267
LCDW form the AABW which is distributed into
the Atlantic, the Indian, and the Pacific Oceans via
the ACC (McCartney 1992).
The western Atlantic ocean receives deepwater directly both from the northern and the southern production area. The relatively warm and saline NADW occupies the depth interval between
2 km and 4 km, whereas AABW is located below
4 km (Fig. 6). The only path where AABW can
enter the western North Atlantic is on the route
through the Equatorial Channel into the Guiana
Basin. In the eastern Atlantic, the Walvis Ridge and
the Mid-Atlantic Ridge bar AABW from entering
the Angola Basin. Only small quantities of AABW
pass the sills eastwards through the Romanche(Van Bennekom and Berger 1984; Warren and
Speer 1991), the Chain Fracture Zone (Mercier et
al. 1994), and the Walvis Passage (Connary and
Ewing 1972; Shannon and Chapman 1991). Thus,
even the deepest parts of these basins are filled
almost exclusively by NADW. In contrast, the
Cape Basin, although located east of the MidAtlantic Ridge, is dominated by AABW below 4,000
m due to a bottom water passage which allows
AABW to enter the basin from the South.
The Indian and the Pacific Oceans are supplied
mainly from the southern source whereas NADW
is added only secondary via the ACC. The North
Pacific Deep Water (NPDW) is the abyssal water mass most abroad from the two domains of
deep-water production. Hence, it carries almost no
NADW. Likewise, NPDW contains the largest
amount of CO 2 , because oxygen is respired almost
totally on its abyssal way to the northern edges of
the Pacific Ocean, which results in sub- to anoxic
pore water.
Samples and Methods
All sediment surface samples from giant box cores
were collected on RIV Meteor cruises (Wefer et
al. 1989; Wefer et al. 1990; Schulz et al. 1992) at
water depths from 1,007 m down to 5,213 m (Fig.
7, Table 2).
The first transect (GeoB 1115-1119) extends
from 3°33'S - 12°35'W over about 345 nm to the
West (2,921 m to 5,213 m water depth) and belongs
to the tropical biogeographic faunal province sensu
Be (1977). The second transect (GeoB 1207-1217)
streches from 24°57'S - 6°44'E over about 85 nm
to the East (2,007 m to 4,669 m water depth); the
third transect (GeoB 1709-1712) ranges from
23°15'S - 12°48'E over about 120 nm to the West
(1,007 m to 3,837 m water depth). Transect 2 and
transect 3 belong to the subtropical biogeographic
faunal province. Hence, all samples within each
transect should be characterized by a more or less
identical faunal association except for the easternmost sample (GeoB 1712), which is located beneath the cold, nutrient rich, and highly productive
Benguela Coastal Current system.
The position of the hydrographic lysocline was
determined sensu Takahashi et al. (1980) and
Broecker and Takahashi (1978) given by the relationship:
(cot),dcite [Ilmol/kgj = 90 . e[a.IO· (W"",deplh[kmj.4)]
(2)
The thickness of the calcite transition zone covers
the range from 10 Ilmol/kg (sensu Broecker and
Peng 1982) to the ACO/' at the CCD (AC0 3 CCD)
sensu Archer (1996).
A LECO CS-125 infrared analyzer was used
in order to measure the total carbon (TC) and the
total organic carbon (TOC) content of bulk
sediments. Calcium carbonate content was calculated in weight percentage of the bulk sample according to the following equation:
CaC0 3 o/o(wlw)=(TC"Io(w/w)- TOC%(wlw»·8.33
(3)
The rain ratio (Berger and Keir 1984) is determined
by the molar ratio of organic (CO,g) to inorganic
(COMb) carbon.
For grain-size analysis as well as for
foraminiferal counts, samples were washed through
a 63 11m sieve under a gentle spray of water to
prevent additional fragmentation. The whole sample >63 Ilm was sieved on a 150 Ilm, 212 Ilm, 355
Ilm, 500 Ilm, and a 1,000 Ilm sieve-set according to
the CLIMAP-conventions (lmbrie and Kipp 1971).
Each fraction was repeatedly split into subsamples
using a microsplitter to obtain an aliquot of at least
300 non-fragmented planktic foraminifera specimens (CLIMAP 1984) that were identified and
counted completely; fragments, benthic
267
LCDW form the AABW which is distributed into
the Atlantic, the Indian, and the Pacific Oceans via
the ACC (McCartney 1992).
The western Atlantic ocean receives deepwater directly both from the northern and the southern production area. The relatively warm and saline NADW occupies the depth interval between
2 km and 4 km, whereas AABW is located below
4 km (Fig. 6). The only path where AABW can
enter the western North Atlantic is on the route
through the Equatorial Channel into the Guiana
Basin. In the eastern Atlantic, the Walvis Ridge and
the Mid-Atlantic Ridge bar AABW from entering
the Angola Basin. Only small quantities of AABW
pass the sills eastwards through the Romanche(Van Bennekom and Berger 1984; Warren and
Speer 1991), the Chain Fracture Zone (Mercier et
al. 1994), and the Walvis Passage (Connary and
Ewing 1972; Shannon and Chapman 1991). Thus,
even the deepest parts of these basins are filled
almost exclusively by NADW. In contrast, the
Cape Basin, although located east of the MidAtlantic Ridge, is dominated by AABW below 4,000
m due to a bottom water passage which allows
AABW to enter the basin from the South.
The Indian and the Pacific Oceans are supplied
mainly from the southern source whereas NADW
is added only secondary via the ACC. The North
Pacific Deep Water (NPDW) is the abyssal water mass most abroad from the two domains of
deep-water production. Hence, it carries almost no
NADW. Likewise, NPDW contains the largest
amount of CO 2 , because oxygen is respired almost
totally on its abyssal way to the northern edges of
the Pacific Ocean, which results in sub- to anoxic
pore water.
Samples and Methods
All sediment surface samples from giant box cores
were collected on RIV Meteor cruises (Wefer et
al. 1989; Wefer et al. 1990; Schulz et al. 1992) at
water depths from 1,007 m down to 5,213 m (Fig.
7, Table 2).
The first transect (GeoB 1115-1119) extends
from 3°33'S - 12°35'W over about 345 nm to the
West (2,921 m to 5,213 m water depth) and belongs
to the tropical biogeographic faunal province sensu
Be (1977). The second transect (GeoB 1207-1217)
streches from 24°57'S - 6°44'E over about 85 nm
to the East (2,007 m to 4,669 m water depth); the
third transect (GeoB 1709-1712) ranges from
23°15'S - 12°48'E over about 120 nm to the West
(1,007 m to 3,837 m water depth). Transect 2 and
transect 3 belong to the subtropical biogeographic
faunal province. Hence, all samples within each
transect should be characterized by a more or less
identical faunal association except for the easternmost sample (GeoB 1712), which is located beneath the cold, nutrient rich, and highly productive
Benguela Coastal Current system.
The position of the hydrographic lysocline was
determined sensu Takahashi et al. (1980) and
Broecker and Takahashi (1978) given by the relationship:
(cot),dcite [Ilmol/kgj = 90 . e[a.IO· (W"",deplh[kmj.4)]
(2)
The thickness of the calcite transition zone covers
the range from 10 Ilmol/kg (sensu Broecker and
Peng 1982) to the ACO/' at the CCD (AC0 3 CCD)
sensu Archer (1996).
A LECO CS-125 infrared analyzer was used
in order to measure the total carbon (TC) and the
total organic carbon (TOC) content of bulk
sediments. Calcium carbonate content was calculated in weight percentage of the bulk sample according to the following equation:
CaC0 3 o/o(wlw)=(TC"Io(w/w)- TOC%(wlw»·8.33
(3)
The rain ratio (Berger and Keir 1984) is determined
by the molar ratio of organic (CO,g) to inorganic
(COMb) carbon.
For grain-size analysis as well as for
foraminiferal counts, samples were washed through
a 63 11m sieve under a gentle spray of water to
prevent additional fragmentation. The whole sample >63 Ilm was sieved on a 150 Ilm, 212 Ilm, 355
Ilm, 500 Ilm, and a 1,000 Ilm sieve-set according to
the CLIMAP-conventions (lmbrie and Kipp 1971).
Each fraction was repeatedly split into subsamples
using a microsplitter to obtain an aliquot of at least
300 non-fragmented planktic foraminifera specimens (CLIMAP 1984) that were identified and
counted completely; fragments, benthic