311
9
Marine Carbonates:
Their Formation and Destruction
RALPH R. SCHNEIDER, HORST D. SCHULZ
AND CHRISTIAN HENSEN
9.1
Introduction
For marine carbonates, an overwhelming amount
of information exists in a variety of specialized
journals addressing marine geochemistry and carbon cycling, as well as in many books summarizing the state of knowledge on this topic. Therefore it would be far beyond the scope of this
chapter to try to completely review what is known
about marine calcareous sediments and their diagenesis. On the other hand, although intensively
investigated since the previous century (e.g. Murray
1897), marine carbonates have gained increasing
attention by marine biologists, geochemists, paleoceanographers and paleoclimatologists over the
last three decades. Among other reasons this is
because marine carbonates, together with the
oceanic CO 2 -carbonic acid-system, act as a sink or
source of carbon within the global carbon cycle
which has become a key topic of investigation and
modelling related to the role of the greenhouse gas
CO 2 in future global climate change.
Descriptions of sedimentary carbonates in different oceanic environments always have dealt
with the formation of the calcium carbonate and
the biologically, physically and chemically mediated processes governing the observed distribution of sedimentary carbonates in the marine
realm. In this context special emphasis was often
given to the complex pattern of inorganic and organic carbon exchange between the atmosphere,
the world ocean and the continents. These are additional factors determining the distribution of inorganic carbon dissolved in seawater and the accumulation or destruction of calcium carbonate in
marine sediments (Berger 1976; Andersen and
Malahoff 1977; Broecker and Peng 1982;
Sundquist and Broecker 1985; Morse and
Mackenzie 1990). The intention of this chapter is
furthermore to review the knowledge on the rate
of calcium carbonate production in the ocean, the
fluxes through the water column, as well as the
rates of inorganic carbon accumulation and destruction in different marine environments. For
this purpose this chapter summarizes studies dealing with the estimation of global carbonate reservoirs and fluxes in the state of ongoing production, accumulation and dissolution or physical
erosion (Milliman 1993; Milliman and Droxler 1996;
Wollast 1994). In addition, this chapter addresses
the principles and presents examples for
calculation of carbonate saturation conditions under variable boundary conditions in the oceanic
CO 2 -carbonic acid-calcite system, i.e. temperature,
pressure, salinity, and CO 2 exchange with the
atmosphere.
9.2
Marine Environments of
Carbonate Production and
Accumulation
This section primarily focuses on the description
of the deposition and accumulation of carbonates
in shallow waters and in the deep ocean. The main
depocenters for calcium carbonates are the
continental shelf areas, as well as island arcs or
atolls, which are the typical shallow water environments for massive carbonate formation, and
the pelagic deep-sea sediments above the calcite
compensation depth catching the rain of small calcareous tests formed by marine plankton in the
surface waters.
9.2.1
Shallow-Water Carbonates
Shallow-water carbonates are formed either by
sediments made up of a variety of carbonate par-
9
Marine Carbonates:
Their Formation and Destruction
RALPH R. SCHNEIDER, HORST D. SCHULZ
AND CHRISTIAN HENSEN
9.1
Introduction
For marine carbonates, an overwhelming amount
of information exists in a variety of specialized
journals addressing marine geochemistry and carbon cycling, as well as in many books summarizing the state of knowledge on this topic. Therefore it would be far beyond the scope of this
chapter to try to completely review what is known
about marine calcareous sediments and their diagenesis. On the other hand, although intensively
investigated since the previous century (e.g. Murray
1897), marine carbonates have gained increasing
attention by marine biologists, geochemists, paleoceanographers and paleoclimatologists over the
last three decades. Among other reasons this is
because marine carbonates, together with the
oceanic CO 2 -carbonic acid-system, act as a sink or
source of carbon within the global carbon cycle
which has become a key topic of investigation and
modelling related to the role of the greenhouse gas
CO 2 in future global climate change.
Descriptions of sedimentary carbonates in different oceanic environments always have dealt
with the formation of the calcium carbonate and
the biologically, physically and chemically mediated processes governing the observed distribution of sedimentary carbonates in the marine
realm. In this context special emphasis was often
given to the complex pattern of inorganic and organic carbon exchange between the atmosphere,
the world ocean and the continents. These are additional factors determining the distribution of inorganic carbon dissolved in seawater and the accumulation or destruction of calcium carbonate in
marine sediments (Berger 1976; Andersen and
Malahoff 1977; Broecker and Peng 1982;
Sundquist and Broecker 1985; Morse and
Mackenzie 1990). The intention of this chapter is
furthermore to review the knowledge on the rate
of calcium carbonate production in the ocean, the
fluxes through the water column, as well as the
rates of inorganic carbon accumulation and destruction in different marine environments. For
this purpose this chapter summarizes studies dealing with the estimation of global carbonate reservoirs and fluxes in the state of ongoing production, accumulation and dissolution or physical
erosion (Milliman 1993; Milliman and Droxler 1996;
Wollast 1994). In addition, this chapter addresses
the principles and presents examples for
calculation of carbonate saturation conditions under variable boundary conditions in the oceanic
CO 2 -carbonic acid-calcite system, i.e. temperature,
pressure, salinity, and CO 2 exchange with the
atmosphere.
9.2
Marine Environments of
Carbonate Production and
Accumulation
This section primarily focuses on the description
of the deposition and accumulation of carbonates
in shallow waters and in the deep ocean. The main
depocenters for calcium carbonates are the
continental shelf areas, as well as island arcs or
atolls, which are the typical shallow water environments for massive carbonate formation, and
the pelagic deep-sea sediments above the calcite
compensation depth catching the rain of small calcareous tests formed by marine plankton in the
surface waters.
9.2.1
Shallow-Water Carbonates
Shallow-water carbonates are formed either by
sediments made up of a variety of carbonate par-