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Fig. 11-9 (a) The vertical distributions of alkalinity (Alk) and dissolved inorganic carbon (DIC) in the world oceans. Ocean regions shown are the North Atlantic (NA), South Atlantic (SA), Antarctic (AA), South Indian (SI), North Indian (NI), South Pacific (SP), and North Pacific (NP) oceans. (Modified with permission from T. Takahashi et al, The alkalinity and total carbon dioxide concentration in the world oceans, in B. Bolin (1981). "Carbon Cycle Modelling," pp. 276-277, John Wiley, Chichester.)

Fig. 11-9 (a) The vertical distributions of alkalinity (Alk) and dissolved inorganic carbon (DIC) in the world oceans. Ocean regions shown are the North Atlantic (NA), South Atlantic (SA), Antarctic (AA), South Indian (SI), North Indian (NI), South Pacific (SP), and North Pacific (NP) oceans. (Modified with permission from T. Takahashi et al, The alkalinity and total carbon dioxide concentration in the world oceans, in B. Bolin (1981). "Carbon Cycle Modelling," pp. 276-277, John Wiley, Chichester.)

the formation of hard parts (i.e., shells, skeletal parts etc.). The very few existing accounts of spontaneous inorganic precipitation of CaC03(s) (so-called "whitings") come from the Bahamas region of the Caribbean (Morse et al, 1984).

The detrital rain of carbon-containing particles can be divided into two groups: the hard parts comprising calcite and aragonite and the soft tissue containing organic carbon. The composition of the soft tissue shows surprising uniformity, the average composition being (CH2O)106 (NH3)i6P04 (see Chapter 10, Section 10.3.1). The average composition of the particulate matter (here a composite of organic and inorganic particles) settling through the water column and subsequently being dissolved in the deep ocean is given by P:N:C:Ca:S = 1:15:131:26:50 (Broecker and Peng, 1982) with a CaC03-C/0rg-C ratio of 1:4. Calculating an average composition of the carbon that actually is deposited in sediments is more difficult since the areas of deposition are different for organic and inorganic carbon. More than 90% of the deposition of organic material takes place on the continental shelves; soft tissues falling into the deep oceans are consumed by heterotrophic organisms before isolation from the water column within the sediments.

The solubility of calcite and aragonite increases with increasing pressure and decreasing temperature in such a way that deep waters are undersaturated with respect to calcium carbonate, while surface waters are supersaturated. The level at which the effects of dissolution are first seen on carbonate shells in the sediments is termed the lysocline and coincides fairly well with the depth of the carbonate saturation horizon. The lysocline commonly lies between 3 and 4 km depth in today's oceans. Below the lysocline is the level where no carbonate remains in the sediment; this level is termed the carbonate compensation depth.

The variations in 14C seen in the deep oceans of the world (Fig. 11-10) show features created

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