Seawater carbonate chemistry

Stanley SM, Hardie LA (1998) Secular oscillations in the carbonate mineralogy of reef-building and sediment-producing organisms driven by tectonically forced shifts in seawater chemistry. Palaeogeography Palaeoclimatology Palaeoecology 144 3-19... 

As previously mentioned, the primary processes responsible for variations in the deep sea C02-carbonic acid system are oxidative degradation of organic matter, dissolution of calcium carbonate, the chemistry of source waters and oceanic circulation patterns. Temperature and salinity variations in deep seawaters are small and of secondary importance compared to the major variations in pressure with depth. Our primary interest is in how these processes influence the saturation state of seawater and, consequently, the accumulation of CaC03 in deep sea sediments. Variations of alkalinity in deep sea waters are relatively small and contribute little to differences in the saturation state of deep seawater. 

More recent calculations such as those in this book indicate substantially lower saturation depths. Those calculated here are plotted in Figure 4.21. The SD is generally about 1 km deeper than that presented by Berger (1977). Clearly the new SD is much deeper than the R0 and appears only loosely related to the FL. Indeed, in the equatorial eastern Atlantic Ocean, the FL is about 600 m shallower than the SD. If these new calculations are even close to correct, the long cherished idea of a "tight" relation between seawater chemistry and carbonate depositional facies must be reconsidered. However, the major control of calcium carbonate accumulation in deep sea sediments, with the exceptions of high latitude and continental slope sediments, generally remains the chemistry of the water. This fact is clearly shown by the differences between the accumulation of calcium carbonate in Atlantic and Pacific ocean sediments, and the major differences in the saturation states of their deep waters. 

Calcium carbonate is accumulating in deep ocean sediments, in which the overlying water is undersaturated with respect to both aragonite and calcite, and sediment marker levels closely correspond to unique saturation states. This indicates that dissolution kinetics play an important role in determining the relation between seawater chemistry and calcium carbonate accumulation in deep ocean basins. It is, therefore, necessary to have knowledge of the dissolution kinetics of calcium carbonate in seawater if the accumulation of calcium carbonate is to be understood. 

Steuber T. and Veizer J. (2002) Phanerozoic record of plate tectonic control of seawater chemistry and carbonate sedimentation. Geology 1123—1126. 

Abstract Laboratory cultures of several species of benthic foraminifera were grown under controlled physical and chemical conditions during months-long experiments carried out at the University of South Carolina in 2001 and 2002. A dozen experimental culture chambers contained a c. 1—3 mm layer of trace-metal free siUca substrate, and were continuously flushed with water from a large (1600 L) seawater reservoir with known, constant temperature and composition (8 0(water), carbonate system chemistry, and trace element concentrations). Each year, in most of the culture chambers, one or more species reproduced, producing hundreds of juveniles which grew into size classes ranging from 100 to 500 microns. Bulimina aculeata was the most successful species in the 2001 cultures, and both B. aculeata and Rosalina vilardeboana were abundant in 2002. 

The construction of CaCOs coccoliths (calcification) leads to additional impacts, over and above those associated with the photosynthesis carried out by all species. The first and perhaps the most important of these is that CaCOs contains carbon and the vertical downward flux of coccoliths thereby removes carbon from the surface oceans. It might be expected that this would lead to additional removal of CO2 from the atmosphere to the oceans, to replace that taken up into coccoliths, but in fact, because of the complex effect of calcification (CaCOs synthesis) on seawater chemistry, the production of coccoliths actually increases the partial pressure of CO2 in surface seawater and promotes outgassing rather than ingassing. Determining the exact nature and magnitude of the overall net effect is complicated by a possible additional role of coccoliths as ballast (coccoliths are denser than water and hence when... 

While there has always been some interest in the nature of the organic compounds in seawater, identification of actual compounds has progressed slowly because of the low concentrations present. With a total organic carbon concentration of 0.5 -1.5 mg/1 of carbon, the total concentration of any single organic compound is likely to be less than 10 7 M. Therefore, in the past, identification of individual compounds has been limited to those few for which specific, sensitive chemical methods existed. These methods were usually spectropho-tometric, and were often developments of methods originally used in clinical chemistry. 

Gershey, R.M., M.D. MacKinnon, P.J. leB Williams, and R.M. Moore. 1979. Comparison of three oxidation methods used for the analysis of the dissolved organic carbon in seawater. Marine Chemistry 7 289-306. 

MacKinnon, M.D. 1981. The measurement of organic carbon in seawater. Pp.415-443 in Marine Organic Chemistry, E.K. Duursma and R. Dawson, eds., New York Elsevier. 

Sugimura, Y., and Y. Suzuki. 1988. A high temperature catalytic oxidation method for the determination of non-volatile dissolved organic carbon in seawater by direct injection of a liquid sample. Marine Chemistry 41 105-131. 

Titration curve for seawater. The shape of the curve is dependent upon experimental conditions. The top curve is produced when seawater is titrated in an open container so that CO2 generated after incremental acid addition can escape into the atmosphere. The bottom curve is generated when seawater is titrated in a closed container. In this case, the pH drops faster during the initial part of the titration because of the build-up of CO2 as acid is added. Once the carbonate/carbonic acid equivalence point is reached, both curves converge upon the same pH for the same volume of acid added, but extensive laboratory work has demonstrated that better accuracy is achieved with the closed container method. Source From Pilson, M. E. Q. (1998). An Introduction to the Chemistry of the Sea. Prentice-Hall, p. 119. 

The above-listed factors concur simultaneously to define the stationary chemistry of seawater. Moreover, the control operated by the various phenomena is selective for the various types of elements for instance, the amounts of Ca are largely controlled by precipitation of carbonates, those of Na and K by silicate hydroly-... 

Sharp, J.H., R. Benner, L. Bermett, C.A. Carlson, S.E. Fitzwater, E.T. Peltzer, and L.M. Tupas. 1995. Analyses of dissolved organic carbon in seawater The JGOFS EQPAC methods comparison. Marine Chemistry 48 91-108. 

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