554
Answers to Problems
Chapter 9
Answer 1
The CaCO 3 production on continental shelves is
about 24.5 · 10 12 moles per year. The carbonate
production of the continental slope areas is only
about 6 · 10 12 moles per year, whereas the production of the pelagic ocean is about 60-90 · 10 12
moles per year (cf. Tab. 9.5).
Answer 2
CaCO 3 production comprises the total amount
produced in the surface waters. Accumulation is
the - much smaller - portion which becomes buried
in the deeper sediment. The difference between
both comprises the dissolution in the water
column and in the upper parts of the young sediment, from where dissolved inorganic carbon
(DIC) still can be transferred to the bottom water.
Thus the sediment below the calcite compensation
depth (CCD) is characterized by no calcite accumulation. Below the CCD calcite particles may
reach the seafloor and may even be found in the
upper few decimeters of the young sediment, but
they will be dissolved according to processes of
early diagenesis.
Answer 3
At high latitudes the calcite compensation depth
(CCD) is at a water depth of about 3000 m,
whereas in low latitudes the CCD is at a depth of
about 5000 m. The undersaturation with respect to
calcite of the deep ocean is caused by cold water,
which sinks to the seafloor at high latitudes and
flows as deep water current towards the low
latitudes. The closer the deep current comes to
the low latitudes, the more calcite from the
production in surface waters is dissolved in the
upper parts of the deep current. Thus the CCD of
the deep water current is continuously lowered on
the way from high to low latitudes.
Answer 4
The predominant carbonate species in normal seawater is bicarbonate (HCO 3
- ), close to 70 % of the
dissolved inorganic carbon (DIC). About 10 % of
the total calcium in normal sea-water exists as
CaSO 4 complex. This complex is rather insignificant in anoxic pore-water if the sulfate is consumed by anaerobic methane oxidation (AOM).
Answer 5
Oxidation of C org results in a production of
dissolved inorganic carbon (DIC) and thus in an
undersaturation of the pore water with respect to
calcite. If calcite is present in the sediment solid
phase, it will be dissolved until saturation is
reached. Due to these reactions the concentration
of DIC in pore-water is usually higher than in
ocean bottom water. This gradient causes a diffusive flux from the sediment to the bottom water.
Upwelling areas are characterized by very high
C org content of the sediment and high fluxes,
deep-sea sediments by low C org content and low
fluxes.
Chapter 10
Answer 1
0.02 · -45 ‰ (ice caps) + 0.98 · 0.0 ‰ (modern
ocean) = -0.9 ‰.
Answer 2
38,000 Gt · 0.3 ‰ +
(modern ocean)
x Gt · -25 ‰ =
(terrestrial carbon)
(38,000 + x) Gt · 0.0 ‰ (glacial ocean)
Therefore: 456 Gt, which is about 20% of the today´s
terrestrial carbon pool. Other explanations would
include the change in ocean pH (LGM: +0.2) and the
resulting influence on δ
13
C values in foraminifers
(Spero et al. 1997) or a change in the ratio of inorganic to organic carbon contributed to the sediments (Derry and France-Lanord 1996).
Answer 3
Using equations (10.9) and (10.13), the effect of
the b-value on pCO 2 would range between 192 and
384 µatm, which underlines the importance of
physiological processes for paleo-PCO 2 determinations.
Answer 4
δ
15
N = 3‰ => f = 0.50
Answers to Problems
Chapter 9
Answer 1
The CaCO 3 production on continental shelves is
about 24.5 · 10 12 moles per year. The carbonate
production of the continental slope areas is only
about 6 · 10 12 moles per year, whereas the production of the pelagic ocean is about 60-90 · 10 12
moles per year (cf. Tab. 9.5).
Answer 2
CaCO 3 production comprises the total amount
produced in the surface waters. Accumulation is
the - much smaller - portion which becomes buried
in the deeper sediment. The difference between
both comprises the dissolution in the water
column and in the upper parts of the young sediment, from where dissolved inorganic carbon
(DIC) still can be transferred to the bottom water.
Thus the sediment below the calcite compensation
depth (CCD) is characterized by no calcite accumulation. Below the CCD calcite particles may
reach the seafloor and may even be found in the
upper few decimeters of the young sediment, but
they will be dissolved according to processes of
early diagenesis.
Answer 3
At high latitudes the calcite compensation depth
(CCD) is at a water depth of about 3000 m,
whereas in low latitudes the CCD is at a depth of
about 5000 m. The undersaturation with respect to
calcite of the deep ocean is caused by cold water,
which sinks to the seafloor at high latitudes and
flows as deep water current towards the low
latitudes. The closer the deep current comes to
the low latitudes, the more calcite from the
production in surface waters is dissolved in the
upper parts of the deep current. Thus the CCD of
the deep water current is continuously lowered on
the way from high to low latitudes.
Answer 4
The predominant carbonate species in normal seawater is bicarbonate (HCO 3
- ), close to 70 % of the
dissolved inorganic carbon (DIC). About 10 % of
the total calcium in normal sea-water exists as
CaSO 4 complex. This complex is rather insignificant in anoxic pore-water if the sulfate is consumed by anaerobic methane oxidation (AOM).
Answer 5
Oxidation of C org results in a production of
dissolved inorganic carbon (DIC) and thus in an
undersaturation of the pore water with respect to
calcite. If calcite is present in the sediment solid
phase, it will be dissolved until saturation is
reached. Due to these reactions the concentration
of DIC in pore-water is usually higher than in
ocean bottom water. This gradient causes a diffusive flux from the sediment to the bottom water.
Upwelling areas are characterized by very high
C org content of the sediment and high fluxes,
deep-sea sediments by low C org content and low
fluxes.
Chapter 10
Answer 1
0.02 · -45 ‰ (ice caps) + 0.98 · 0.0 ‰ (modern
ocean) = -0.9 ‰.
Answer 2
38,000 Gt · 0.3 ‰ +
(modern ocean)
x Gt · -25 ‰ =
(terrestrial carbon)
(38,000 + x) Gt · 0.0 ‰ (glacial ocean)
Therefore: 456 Gt, which is about 20% of the today´s
terrestrial carbon pool. Other explanations would
include the change in ocean pH (LGM: +0.2) and the
resulting influence on δ
13
C values in foraminifers
(Spero et al. 1997) or a change in the ratio of inorganic to organic carbon contributed to the sediments (Derry and France-Lanord 1996).
Answer 3
Using equations (10.9) and (10.13), the effect of
the b-value on pCO 2 would range between 192 and
384 µatm, which underlines the importance of
physiological processes for paleo-PCO 2 determinations.
Answer 4
δ
15
N = 3‰ => f = 0.50