102
3
Quantification of Early Diagenesis: Dissolved Constituents in Marine Pore Water
remains at the bottom phase of the bottle. Even
though the compound is not as toxic in humans as
those previously mentioned, no one would think
of pipetting the sample thus (or otherwise) treated
by mouth. It is anticipated that these toxified samples have a shelf-life of about 4 weeks.
Previously, water samples were often frozen.
This procedure is not at all suited for marine pore
water because mineral precipitations might occur.
These precipitations do not become soluble upon
thawing the samples, hence the pore water samples have become irreversibly damaged.
3.4
Analyzing Constituents in
Pore Water, Typical Profiles
This section does not claim to re-write the analytical treatment of sea water anew, nor is it
intended to present this aspect as a mere recapitulation of facts which will be far from being
complete. This task would by far exceed the possibilities and, above all, the scope of this book.
However, analytical methods are subject to continual improvement and relatively fast changes so
that many of the methods to be introduced here
would soon become outdated. Therefore, only a
short account of the current methods will be
given, especially of those that demand comment
on the specificity to marine pore water.
The analytical details of methods that are currently used in the examination of marine pore
water can be looked up in the internet under the
following address:
http://www.geochemie.uni-bremen.de
We will take it upon ourselves to continually update the internet page, to evaluate the suggestions
we receive for improvement, and eventually make
this information available to other researchers.
If we take for granted that, in each single case,
the determination of oxygen dissolved in marine
pore water, as well as the measurement of the pHvalue, E H -value, and certainly the measurement of
the temperature as well, has already been performed, the following sequence of single analytical
steps is applied to the pressed or centrifuged pore
water samples:
• The titration of alkalinity must be carried out
as quickly as possible, i.e., within minutes or
maximally within one hour, as a replacement
to the direct determination of carbonate. Especially when high alkalinity values are
present (maximal values up to 100 mmol(eq) l
-1
are known to occur in pore water, whereas
sea water contains only about 2.5 mmol(eq) l
-1
),
the adjustment to atmospheric pCO 2 might
induce too low alkalinity values due to precipitation of calcite within the sample.
• If sampling for methane and sulfide has been
performed as described above (see Sect. 3.3.2
‘Analyses of Dissolved Gases’), the analytical measurement of the already preserved
samples does not have to take place immediately within the first few minutes. Yet, the
analysis should not be deferred for more than
a couple of hours.
• Analyzing compounds that are sensitive to
microbial action (phosphate, ammonium,
nitrate, nitrite, silica) should always be
completed approximately within one day, if
the samples were not preserved by the addition of TTE (trifluorotrichloroethane). Even in
its preserved state, it is not recommended to
store the sample for longer than four weeks.
Storage is best in the dark at about 4°C; freezing the samples is not recommended.
• The determination of sulfate and halogenides
is not coupled to any particular time. It must
be ascertained that no evaporation of the
sample is likely to occur. Other instances of
sample perturbation are not known. Storage
is best at about 4°C; freezing the samples is
not recommended.
Photometrical Determinations, Auto-Analyzer
Most procedures for photometric analysis of sea
water samples were described by Grasshoff et al.
(1999). Owing to the quicker processing speed,
and especially the need to apply lower amounts of
sample solution, one would generally employ the
auto-analyzer method to this end. The method is
also described in the aforementioned textbook.
The auto-analyzer can be either self-built or may
be purchased from diverse commercial suppliers
as a ready-to-use appliance. The analysis of
marine pore water is generally characterized by
small sample volumes and, as for some parameters,
concentrations that are distinctly different from
3
Quantification of Early Diagenesis: Dissolved Constituents in Marine Pore Water
remains at the bottom phase of the bottle. Even
though the compound is not as toxic in humans as
those previously mentioned, no one would think
of pipetting the sample thus (or otherwise) treated
by mouth. It is anticipated that these toxified samples have a shelf-life of about 4 weeks.
Previously, water samples were often frozen.
This procedure is not at all suited for marine pore
water because mineral precipitations might occur.
These precipitations do not become soluble upon
thawing the samples, hence the pore water samples have become irreversibly damaged.
3.4
Analyzing Constituents in
Pore Water, Typical Profiles
This section does not claim to re-write the analytical treatment of sea water anew, nor is it
intended to present this aspect as a mere recapitulation of facts which will be far from being
complete. This task would by far exceed the possibilities and, above all, the scope of this book.
However, analytical methods are subject to continual improvement and relatively fast changes so
that many of the methods to be introduced here
would soon become outdated. Therefore, only a
short account of the current methods will be
given, especially of those that demand comment
on the specificity to marine pore water.
The analytical details of methods that are currently used in the examination of marine pore
water can be looked up in the internet under the
following address:
http://www.geochemie.uni-bremen.de
We will take it upon ourselves to continually update the internet page, to evaluate the suggestions
we receive for improvement, and eventually make
this information available to other researchers.
If we take for granted that, in each single case,
the determination of oxygen dissolved in marine
pore water, as well as the measurement of the pHvalue, E H -value, and certainly the measurement of
the temperature as well, has already been performed, the following sequence of single analytical
steps is applied to the pressed or centrifuged pore
water samples:
• The titration of alkalinity must be carried out
as quickly as possible, i.e., within minutes or
maximally within one hour, as a replacement
to the direct determination of carbonate. Especially when high alkalinity values are
present (maximal values up to 100 mmol(eq) l
-1
are known to occur in pore water, whereas
sea water contains only about 2.5 mmol(eq) l
-1
),
the adjustment to atmospheric pCO 2 might
induce too low alkalinity values due to precipitation of calcite within the sample.
• If sampling for methane and sulfide has been
performed as described above (see Sect. 3.3.2
‘Analyses of Dissolved Gases’), the analytical measurement of the already preserved
samples does not have to take place immediately within the first few minutes. Yet, the
analysis should not be deferred for more than
a couple of hours.
• Analyzing compounds that are sensitive to
microbial action (phosphate, ammonium,
nitrate, nitrite, silica) should always be
completed approximately within one day, if
the samples were not preserved by the addition of TTE (trifluorotrichloroethane). Even in
its preserved state, it is not recommended to
store the sample for longer than four weeks.
Storage is best in the dark at about 4°C; freezing the samples is not recommended.
• The determination of sulfate and halogenides
is not coupled to any particular time. It must
be ascertained that no evaporation of the
sample is likely to occur. Other instances of
sample perturbation are not known. Storage
is best at about 4°C; freezing the samples is
not recommended.
Photometrical Determinations, Auto-Analyzer
Most procedures for photometric analysis of sea
water samples were described by Grasshoff et al.
(1999). Owing to the quicker processing speed,
and especially the need to apply lower amounts of
sample solution, one would generally employ the
auto-analyzer method to this end. The method is
also described in the aforementioned textbook.
The auto-analyzer can be either self-built or may
be purchased from diverse commercial suppliers
as a ready-to-use appliance. The analysis of
marine pore water is generally characterized by
small sample volumes and, as for some parameters,
concentrations that are distinctly different from