Compensation depth

Biogenic Ma.teria.ls, Deep ocean calcareous or siUceous oo2es are sediments containing >30% of biogenic material. Foraminifera, the skeletal remains of calcareous plankton, are found extensively in deep equatorial waters above the calcium carbonate compensation depth of 4000 to 5000 m. 

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. 

Figure 5. Downcore profile of 6 Zn (Marechal et al. 2000) and 6 Cu values (unpublished) in Central Pacific core RC 17-203 (21° 50 S, 132° 53 W, z = 3900 m). The water-sediment interface is located below the carbonate compensation depth and deep-sea clays dominate the mineralogy of the samples.

Calcite compensation depth See Calcium carbonate compensation depth. 

Calcium carbonate compensation depth (CCD) The depth below which calcium carbonate is not found in marine sediments due to its dissolution. 

Carbonate compensation The ocean s response to perturbations through shifts in its carbonate chemistry. These shifts require changes in the carbonate ion concentration that change the depth of the calcium carbonate compensation depth and hence lead to changes in the burial rate of carbon as biogenic calcium carbonate. 

Ben-Yaakov, S., Ruth, E., and Kaplan, I. R. Carbonate compensation depth Relation to carbonate solubility in ocean waters. Science 184, 982-984 (1974). 

Betzer et al. (1984, 1986) studied the sedimentation of pteropods and foraminifera in the North Pacific. Their sediment trap results confirmed that considerable dissolution of pteropods was taking place in the water column. They calculated that approximately 90% of the aragonite flux was remineralized in the upper 2.2 km of the water column. Dissolution was estimated to be almost enough to balance the alkalinity budget for the intermediate water maximum of the Pacific Ocean. It should be noted that the depth for total dissolution in the water column is considerably deeper than the aragonite compensation depth. This is probably due to the short residence time of pteropods in the water column because of their rapid rates of sinking. 

Figure 10.20. Comparison of some trends through the Cenozoic. A. The 8180 content of benthic foraminifera (Savin et al., 1975 see also Prentice and Matthews, 1988). If the 5180 trend is primarily due to temperature, Cretaceous deep water temperatures were about 12°C warmer than today. B. Progressive change of the North Atlantic and Pacific carbonate compensation depth (CCD van Andel, 1975). C. The Sr/Ca ratio of planktonic foraminifera (Graham et al., 1982). D. Ridge volume (Pitman, 1978).

Berger W.H. (1978) Deep-sea carbonate Pteropod distribution and the aragonite compensation depth. Deep-Sea Res. 25,447-452. 

Heath G.R. and Culberson C. (1970) Calcite Degree of saturation, rate of dissolution, and the compensation depth in the deep oceans. Geol. Soc. Amer. Bull. 81, 3157-3160. 

Pytkowicz R.M. (1970) On the carbonate compensation depth in the Pacific Ocean. Geochim. Cosmochim. Acta 34, 836-839. 

Figure 7. The depth distribution of the Ro and calcite saturation levels, the foraminiferal lysocline and the calcium carbonate compensation depth in the Western and Eastern Atlantic Ocean (after Ref. 40)...

Takahashi, T. Carbonate chemistry of seawater and the calcite compensation depth in the oceans, p. 11-26, ... 

At about 4000 m water depth, carbonate tests are dissolved, because their solubility depends on pressure (this depth in the ocean is called calcite compensation depth, abbreviated CCD). With the dissolution of tests the metals collected before are again liberated and can contribute to the growth of manganese nodules. 

Natural populations of Trichodesmium which are often found in the upper layers of the euphotic zone (see Chapter 16 by Karl et al, this volume), appear to be adapted to high light with a relatively shallow compensation depth (typically 100-200 imol quanta s ) for photosynthesis (Carpenter, 1983a,b LaRoche and Breitbarth, 2005). Several early studies considered the light-photosynthesis relationships o Trichodesmium (e.g., Lewis et al, 1988 Li et al, 1980). Half saturation (4) constants for photosynthesis are reported to be about 300 pmol quanta m s (based on results from four studies, LaRoche and Breitbarth, 2005). See LaRoche and Breitbarth (2005) for a recent comprehensive summary of observed physiological and photosynthetic parameters for Trichodesmium. 

---