435
12.3
The Interpretation of Patterns of Regionally Distributed Data
are related to the formation of sub- and anoxic
microenvironments. Burial of larger particles
stemming from organisms and fecal pellets may
create hotspots of microbial activity within the
sediment. Locally restricted deficits of oxidants,
particularly of oxygen and nitrate, are the consequence. In this context Jørgensen (1977) reported
reducing microniches of about 50-200µm in
diameter, where sulfate reduction may take place
in a basically oxidized environment. The retardation of diffusion is likely caused by the formation of organic coatings or precipitation processes
narrowing the pore space. Developing a simple
mathematical model, Jahnke (1985) could already
show that processes in microenvironments can
affect pore water profiles in a different way.
Applying a three-dimensional model to results of
high resolution DGT profiles (see Section 3.5)
Harper et al. (1999) concluded that the common onedimensional view of the system may underestimate
relevant process rates by a factor of at least 3.
For the sake of completeness, advective effusions also need to be mentioned here (see
Chapters 13 and 14). Although their significance
for global balances of materials (e.g. CO 2 , see
Chapter 5) has been hardly investigated yet, the
hot vents and cold seeps, usually locally confined, seem to be rather unimportant for the
interaction described here. Nevertheless, they
may be relevant when looking on specific element
cycles (e.g. Li, B or Ba).
In summary, knowledge of the applied methods
and the local conditions is indispensable for the
compilation of a database which should be as
homogenous as possible. However, a clearly
defined objective is required for characterizing
patterns of regional and global distributions in
order to successfully avoid illicit comparisons. As
we will see, to merely resign to data produced
under identical conditions is by no means a
realistic conclusion. Good judgment is always of
ultimate importance. Table 12.1 gives an overview
on the important aspects of this section.
12.3 The Interpretation of Patterns
of Regionally Distributed Data
One important objective in characterizing regional
differences of early diagenetic processes is to
obtain information on the rate-determining control
parameters and the benthic material fluxes. It has
been stated before that, for various reasons, there
can be no global database covering all biogeochemical and sedimentary environments. It is
therefore only possible to design global balances
of geochemical material cycles by means of deterministic approaches. It is thus reasonable to focus
on those control parameters with the highest data
density available, which are for example primary
production or the C org content of surface sediments (see Section 12.5).
The interrelations between the individual areas
of the oceans have already been outlined at the
beginning of this chapter. Owing to an intense
research of the last decades, many principles of
interaction and modes of possible interference
among single processes could be demonstrated
(e.g. a high rate of primary production yields large
amounts of organic substance in the sediment,
which intensifies the growth of benthic populations; cf. Section 12.2.2). According to the
principle of actuality, any statement on environmental changes in Earth’s history, as well as any
prognoses on global change in the future, must be
based on a thorough understanding of the present
situation. However, empirical relations mostly
apply only for a limited range of locations. In the
following, the most important control parameters
will be presented, along with a brief comment on
the potential relevance they have for the benthic
interface.
12.3.1 Input and Accumulation
of Organic Material
The amount of nutrients recycled back to the
ocean by benthic processes is closely related to
the availability of organic substances, which can
be degraded by microorganisms (cf. Chapters 310). There are two fundamental strategies to
make use of this correlation as a control
parameter for the benthic biogeochemical system
and as a tool for the estimation of benthic material fluxes.
An indirect way to estimate the amount of
organic substance in the benthic system uses
the close coupling between the biological phytoplankton reproduction in the photic zone with
the C org rain to the ocean bottom. The overall
advantage of this approach is that satellite data
are available in high resolution in space and
time, respectively (e.g. Antoine et al. 1996;
Behrenfeld and Falkowski 1997; http://www.
Oceancolor.gsfc.nasa.gov/SeaWiFS/). Figure 12.6
12.3
The Interpretation of Patterns of Regionally Distributed Data
are related to the formation of sub- and anoxic
microenvironments. Burial of larger particles
stemming from organisms and fecal pellets may
create hotspots of microbial activity within the
sediment. Locally restricted deficits of oxidants,
particularly of oxygen and nitrate, are the consequence. In this context Jørgensen (1977) reported
reducing microniches of about 50-200µm in
diameter, where sulfate reduction may take place
in a basically oxidized environment. The retardation of diffusion is likely caused by the formation of organic coatings or precipitation processes
narrowing the pore space. Developing a simple
mathematical model, Jahnke (1985) could already
show that processes in microenvironments can
affect pore water profiles in a different way.
Applying a three-dimensional model to results of
high resolution DGT profiles (see Section 3.5)
Harper et al. (1999) concluded that the common onedimensional view of the system may underestimate
relevant process rates by a factor of at least 3.
For the sake of completeness, advective effusions also need to be mentioned here (see
Chapters 13 and 14). Although their significance
for global balances of materials (e.g. CO 2 , see
Chapter 5) has been hardly investigated yet, the
hot vents and cold seeps, usually locally confined, seem to be rather unimportant for the
interaction described here. Nevertheless, they
may be relevant when looking on specific element
cycles (e.g. Li, B or Ba).
In summary, knowledge of the applied methods
and the local conditions is indispensable for the
compilation of a database which should be as
homogenous as possible. However, a clearly
defined objective is required for characterizing
patterns of regional and global distributions in
order to successfully avoid illicit comparisons. As
we will see, to merely resign to data produced
under identical conditions is by no means a
realistic conclusion. Good judgment is always of
ultimate importance. Table 12.1 gives an overview
on the important aspects of this section.
12.3 The Interpretation of Patterns
of Regionally Distributed Data
One important objective in characterizing regional
differences of early diagenetic processes is to
obtain information on the rate-determining control
parameters and the benthic material fluxes. It has
been stated before that, for various reasons, there
can be no global database covering all biogeochemical and sedimentary environments. It is
therefore only possible to design global balances
of geochemical material cycles by means of deterministic approaches. It is thus reasonable to focus
on those control parameters with the highest data
density available, which are for example primary
production or the C org content of surface sediments (see Section 12.5).
The interrelations between the individual areas
of the oceans have already been outlined at the
beginning of this chapter. Owing to an intense
research of the last decades, many principles of
interaction and modes of possible interference
among single processes could be demonstrated
(e.g. a high rate of primary production yields large
amounts of organic substance in the sediment,
which intensifies the growth of benthic populations; cf. Section 12.2.2). According to the
principle of actuality, any statement on environmental changes in Earth’s history, as well as any
prognoses on global change in the future, must be
based on a thorough understanding of the present
situation. However, empirical relations mostly
apply only for a limited range of locations. In the
following, the most important control parameters
will be presented, along with a brief comment on
the potential relevance they have for the benthic
interface.
12.3.1 Input and Accumulation
of Organic Material
The amount of nutrients recycled back to the
ocean by benthic processes is closely related to
the availability of organic substances, which can
be degraded by microorganisms (cf. Chapters 310). There are two fundamental strategies to
make use of this correlation as a control
parameter for the benthic biogeochemical system
and as a tool for the estimation of benthic material fluxes.
An indirect way to estimate the amount of
organic substance in the benthic system uses
the close coupling between the biological phytoplankton reproduction in the photic zone with
the C org rain to the ocean bottom. The overall
advantage of this approach is that satellite data
are available in high resolution in space and
time, respectively (e.g. Antoine et al. 1996;
Behrenfeld and Falkowski 1997; http://www.
Oceancolor.gsfc.nasa.gov/SeaWiFS/). Figure 12.6