550
Answers to Problems
Analysis by weight and volume primarily determines the wet bulk density, gamma ray attenuation
the wet bulk density (by assumption of a processing porosity), and electrical resitivity the porosity.
Porosity values can be converted to density values
(and vice versa) by using equation 2.3.
Answer 3
Calcareous and siliceous sediment differ
significantly by their sediment grain density. It
amounts to about 2.7 g cm
-3
for calcareous ooze
and to about 2.1 g cm
-3
for siliceous ooze, so that a
downcore grain density model has to be developed
from the carbonate (and opal) content, in order to
calculate wet bulk densities from porosities.
Answer 4
The (mean) grain size mainly influences the
ultrasonic wave propagation. P-wave velocity and
attenuation increases with increasing (mean) grain
sizes.
Answer 5
The strength of a reflection horizon is determined
by the reflection coefficient R = (I 2 - I 1 ) / (I 2 + I 1 ),
which depends on the acoustic impedance
contrast of the two adjacent layers. The acoustic
impedance (I) depends on the P-wave velocity (v P )
and wet bulk density (ρ) and is defined as the
product of both parameters, I = v P ρ.
Chapter 3
Answer 1
Measurement in fresh sediment: oxygen, pH-value,
sulfide. As soon as possible in squeezed or
centrifuged pore water: alkalinity, ammonia, total
iron. After preservation within some weeks:
manganese, nitrate, potassium. Without preservation even after long time: chloride, sodium,
sulfate.
Answer 2
Diffusion coefficient in seawater D
SW
for SO 4
2at
5°C is 5.72E-10 m
2
s
-1
. Tortuosity for a sediment
with a porosity of φ = 0.7 is θ
2
= 1.71. Diffusion
coefficient for SO 4
2in pore water under these
conditions is D sed = 3.3E-10 m
2
s
-1
. The gradient in
the depth interval between 0 and 6 m is 28 mol m
-3
per 6 m = 4.7 mol m
-3
m
-1
. The downward flux of
SO 4
2is J sed = 0.7 · 3.3E-10 · 4.7 mol m
-2
s
-1
= 1.1E-9
mol m
-2
s
-1
or 34 mmol m
-2
a
-1
.
Answer 3
Diffusion coefficient in seawater D
SW
for O 2 at 5°C
is 1.23E-9 m
2
s
-1
. Tortuosity for a sediment with a
porosity of φ = 0.7 is θ
2
= 1.71. Diffusion coefficient
for O 2 in pore water under these conditions is D sed =
7.2E-10 m
2
s
-1
. The steepest gradient close to the
sediment surface (depth interval between 0 and ca.1
mm) is 28 mol m
-3
m
-1
. The downward flux of O 2 is J sed
= 0.7 · 7.2E-10 · 28 mol m
-2
s
-1
= 1.4E-8 mol m
-2
s
-1
or
0.45 mol m
-2
a
-1
. With an O 2 /DIC-ratio of 138/106
(cf. Eq. 3.10 and Fig. 3.11) this rate is equivalent to
0.34 mol DIC m
-2
a
-1
or 4.1 g C m
-2
a
-1
.
Answer 4
A glove box with an inert gas atmosphere is
necessary for all steps from sampling to analyzing
anoxic pore water and/or sediment for constituents which would be oxidized in contact with
the normal atmosphere. Such constituents are e.g.
Fe
2+
, Mn
2+
, NH 4
+
, S
2. Only especially pure and
expensive nitrogen does not contain interfering
oxygen concentration. Normal argon usually
contains sufficiently low oxygen concentration
and is much cheaper.
Answer 5
Elements of mainly terrestrial origin are: Ti, Al, Fe,
K, Rb, Mg. A mainly marine input is characteristic
for Ca, Sr, (Ba). The elements Mn, S, (Fe) reach the
sediment solid phase mainly by diagenetic
processes.
Chapter 4
Answer 1
Enrichment of organic matter in marine sediments
is mainly favored by the combined effects of low
oxygen concentrations, either already in the water
column or at shallow depth in the pore water
system of the sediments, and high sedimentation
Answers to Problems
Analysis by weight and volume primarily determines the wet bulk density, gamma ray attenuation
the wet bulk density (by assumption of a processing porosity), and electrical resitivity the porosity.
Porosity values can be converted to density values
(and vice versa) by using equation 2.3.
Answer 3
Calcareous and siliceous sediment differ
significantly by their sediment grain density. It
amounts to about 2.7 g cm
-3
for calcareous ooze
and to about 2.1 g cm
-3
for siliceous ooze, so that a
downcore grain density model has to be developed
from the carbonate (and opal) content, in order to
calculate wet bulk densities from porosities.
Answer 4
The (mean) grain size mainly influences the
ultrasonic wave propagation. P-wave velocity and
attenuation increases with increasing (mean) grain
sizes.
Answer 5
The strength of a reflection horizon is determined
by the reflection coefficient R = (I 2 - I 1 ) / (I 2 + I 1 ),
which depends on the acoustic impedance
contrast of the two adjacent layers. The acoustic
impedance (I) depends on the P-wave velocity (v P )
and wet bulk density (ρ) and is defined as the
product of both parameters, I = v P ρ.
Chapter 3
Answer 1
Measurement in fresh sediment: oxygen, pH-value,
sulfide. As soon as possible in squeezed or
centrifuged pore water: alkalinity, ammonia, total
iron. After preservation within some weeks:
manganese, nitrate, potassium. Without preservation even after long time: chloride, sodium,
sulfate.
Answer 2
Diffusion coefficient in seawater D
SW
for SO 4
2at
5°C is 5.72E-10 m
2
s
-1
. Tortuosity for a sediment
with a porosity of φ = 0.7 is θ
2
= 1.71. Diffusion
coefficient for SO 4
2in pore water under these
conditions is D sed = 3.3E-10 m
2
s
-1
. The gradient in
the depth interval between 0 and 6 m is 28 mol m
-3
per 6 m = 4.7 mol m
-3
m
-1
. The downward flux of
SO 4
2is J sed = 0.7 · 3.3E-10 · 4.7 mol m
-2
s
-1
= 1.1E-9
mol m
-2
s
-1
or 34 mmol m
-2
a
-1
.
Answer 3
Diffusion coefficient in seawater D
SW
for O 2 at 5°C
is 1.23E-9 m
2
s
-1
. Tortuosity for a sediment with a
porosity of φ = 0.7 is θ
2
= 1.71. Diffusion coefficient
for O 2 in pore water under these conditions is D sed =
7.2E-10 m
2
s
-1
. The steepest gradient close to the
sediment surface (depth interval between 0 and ca.1
mm) is 28 mol m
-3
m
-1
. The downward flux of O 2 is J sed
= 0.7 · 7.2E-10 · 28 mol m
-2
s
-1
= 1.4E-8 mol m
-2
s
-1
or
0.45 mol m
-2
a
-1
. With an O 2 /DIC-ratio of 138/106
(cf. Eq. 3.10 and Fig. 3.11) this rate is equivalent to
0.34 mol DIC m
-2
a
-1
or 4.1 g C m
-2
a
-1
.
Answer 4
A glove box with an inert gas atmosphere is
necessary for all steps from sampling to analyzing
anoxic pore water and/or sediment for constituents which would be oxidized in contact with
the normal atmosphere. Such constituents are e.g.
Fe
2+
, Mn
2+
, NH 4
+
, S
2. Only especially pure and
expensive nitrogen does not contain interfering
oxygen concentration. Normal argon usually
contains sufficiently low oxygen concentration
and is much cheaper.
Answer 5
Elements of mainly terrestrial origin are: Ti, Al, Fe,
K, Rb, Mg. A mainly marine input is characteristic
for Ca, Sr, (Ba). The elements Mn, S, (Fe) reach the
sediment solid phase mainly by diagenetic
processes.
Chapter 4
Answer 1
Enrichment of organic matter in marine sediments
is mainly favored by the combined effects of low
oxygen concentrations, either already in the water
column or at shallow depth in the pore water
system of the sediments, and high sedimentation