Carbon deep water

Similar deposits of radiolaria or diatoms composed of siUceous skeletal remains are widespread in more temperate areas in deep water below 5000 m. The deposits maybe very pure. The diatoms recovered from deposits on land are used as fillers or filter materials or as a source of high quaUty carbonate or sihca (see Diatomite). 

A number of current coupled ocean-atmosphere climate models predict that the overturning of the North Atlantic may decrease somewhat under a future warmer climate.While this is not a feature that coupled models deal with well, its direct impact on the ocean s sequestration of carbon would be to cause a significant decline in the carbon that is stored in the deep water. This is a positive feedback, as oceanic carbon uptake would decline. Flowever, the expansion of area populated by the productive cool water plankton, and the associated decline... 

Fig. 10-12 The A C values of the cores of the North Atlantic, Pacific, and Indian Ocean deep waters. The oldest waters are encountered near 40°N in the Pacific Ocean. (Modified with permission from M. Stuiver et al. (1983). Abyssal water carbon-14 distribution and the age of the world oceans. Science 219 849-851, the AAAS.)...

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. 

Shackleton NJ, Imbrie J, Hall MA (1983) Oxygen and carbon isotope record of East Pacific core V19-30 implications for the formation of deep water in the late Pleistocene Nodh Atlantic. Earth Planet Sci... 

In order to use a single subroutine to perform the same calculation on different input values, I must first specify the values, then call the subroutine, and finally save the result. An example here is the call to CARBONATE in subroutine OTHER. I have set this call up with what looks in this program like needless complexity so that I can later make a second call to CARBONATE in order to calculate deep-water properties as well as shallow-water properties. 

Another indication that the use of reference materials has improved oceanographic data quality can be seen by examining the degree of agreement between measurements for deep water masses obtained where two separate cruises intersect. Lamb et al. (2002) examined this in detail for cruises in the Pacific Ocean and showed that the measurements of total DIC (for cruises where reference materials were available) typically agreed to within 2 pmol/kg (Fig. 2.3). This is in sharp contrast to the required adjustments to previous oceanic carbon data sets over the years. 

The concentration of POM remineralized since a deep-water mass was last at the sea surface can be calculated using this ratio. For example, the highest AOU shown in Figme 8.2 occms in the North Pacific. The amoimt of organic carbon that must be... 

As a water mass ages, the ratio of [CO3 ] to [HCO3] declines because the continuing generation of CO2 from the remineralization of POC pushes the equilibrium reaction in Eq. 15.18 further toward the products. Thus, as a deep water mass ages, it becomes increasingly more undersaturated with respect to biogenic calcium carbonate. 

Although surfece waters are supersaturated with respect to calcium carbonate, abiogenic precipitation is imcommon, probably because of unfevorable kinetics. (The relatively rare formation of abiogenic calcite is discussed further in Chapter 18.) Marine organisms are able to overcome this kinetic barrier because they have enzymes that catalyze the precipitation reaction. Because fl declines with depth, organisms that deposit calcareous shells in deep waters, such as benthic foraminiferans, must expend more energy to create their hard parts as compared to surfece dwellers. 

North Atlantic to 500 m in the North Pacific. This reflects an increasing addition of CO2 to deep waters as meridional overturning circulation moves them from the Atlantic to the Indian and then to the Pacific Ocean. Thus, as a water mass ages, it becomes more corrosive to calcium carbonate. Since aragonite is more soluble than calcite, its saturation horizon lies at shallower depths, rising from 3000 m in the North Atlantic to 200 m in the North Pacific. 

As with the calcareous tests, BSi dissolution rates depend on (1) the susceptibility of a particular shell type to dissolution and (2) the degree to which a water mass is undersaturated with respect to opaline silica. Susceptibility to dissolution is related to chemical and physical factors. For example, various trace metals lower the solubility of BSi. (See Table 11.6 for the trace metal composition of siliceous shells.) From the physical perspective, denser shells sink fester. They also tend to have thicker walls and lower surface-area-to-volume ratios, all of which contribute to slower dissolution rates. As with calcivun carbonate, the degree of saturation of seawater with respect to BSi decreases with depth. The greater the thermodynamic driving force for dissolution, the fester the dissolution rate. As shown in Table 16.1, vertical and horizontal segregation of DSi does not significantly coimter the effect of pressure in increasing the saturation concentration DSi. Thus, unlike calcite, there is no deep water that is more thermodynamically favorable for BSi preservation they are all corrosive to BSi. 

The oceanic carbon inventory was presented in Table 15.3. Most of the carbon is inorganic (98%), predominantly in the form of bicarbonate (87%), and is located in the intermediate and deep waters. Of the 2% that is organic, the majority is DOC (see Table 23.2). At present, the ocean is acting as a net sink for atmospheric CO2. In the modern-day carbon cycle, the sole oceanic sink fitr carbon is burial in the sediments in the form of detrital biogenic PIC and POC. 

This is the case generally encountered in geochemical investigations a deep water is sampled and total carbonates and pH are determined to solve the question of whether or not the sampled water was in equilibrium with calcite (or other carbonates) at the T and P of sampling. The system is clearly determined the equilibria to be considered in this case are those of equations 8.73, 8.74, and 8.77 (eq. 8.76, 8.80, and 8.81 have no influence). 

Table 8.8 Compositions of superficial and deep waters of the Sarcidano region (Sardinia, Italy) equilibriated with Mesozoic dolomite limestones (Bertorino et ah, 1981). Values in mEq/1. C-j- total inorganic carbon in mmol/1.

Another application of carbon isotopes in foraminifera is to distinguish distinct water masses and to trace deep water circulation (Bender and Keigwin 1979 Duplessy et al. 1988). Since dissolved carbonate in the deeper waters becomes iso-topically lighter with time and depths in the area of their formation due to the increasing oxidation of organic material, comparison of sites of similar paleodepth in different areas can be used to trace the circulation of deep waters as they move from their sources. Such a reconstruction can be carried out by analyzing 8 C-values of well-dated foraminifera. 

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