In marine sediments

H. L. Windom, "Lithogenous Matedal in Marine Sediments," Chemical Oceanography, Academic Press, Inc., New York, 1976. 

The formation and dissolution of CaCOa in the ocean plays a significant role in all of these effects (34)- CaCOa is produced by marine organisms at a rate several times the supply rate of CaCOa to the sea from rivers. Thus, for the loss of CaCOa to sediments to match the supply from rivers, most of the CaCOa formed must be redissolved. The balance is maintained through changes in the [COa] content of the deep sea. A lowering of the CO2 concentration of the atmosphere and ocean, for example by increased new production, raises the [COa] ion content of sea water. This in turn creates a mismatch between CaCOa burial and CaCOa supply. CaCOa accumulates faster than it is supplied to the sea. This burial of excess CaCOa in marine sediments draws down the [COa] - concentration of sea water toward the value required for balance between CaCOa loss and gain. In this way, the ocean compensates for organic removal. As a consequence of this compensation process, the CO2 content of the atmosphere would rise back toward its initial value. 

Table 3-1 Electron acceptors that are used in the biodegradation of organic material in marine sediments. More on the chemistry of these processes is presented in Chapters 8 and 16...

In marine sediments, usually only the uppermost layer of the sediment exhibits oxidizing conditions while the rest is reduced. The thickness of the oxidized layer and the reducing capacity of the sediment below depend on ... 

The annual primary production of organic carbon through photosynthesis is on the order of 70 Pg/yr. The major part of this carbon is decomposed or respired in a process that also involves the biogeochemical transformation of nitrogen, sulfur, and many other elements. Only a small part of the annual primary production of organic carbon escapes decomposition and is buried in marine sediments. On average. 

The carbonate system plays a pivotal role in most global cycles. For example, gas exchange of CO2 is the exchange mechanism between the ocean and atmosphere. In the deep sea, the concentration of COi ion determines the depth at which CaCOs is preserved in marine sediments. 

MacKenzie and Garrels equilibrium models. Most marine clays appear to be detrital and derived from the continents by river or atmospheric transport. Authigenic phases (formed in place) are found in marine sediments (e.g. Michalopoulos and Aller, 1995), however, they are nowhere near abundant enough to satisfy the requirements of the river balance. For example, Kastner (1974) calculated that less than 1% of the Na and 2% of the K transported by rivers is taken up by authigenic feldspars. 

The failure to identify the necessary authigenic silicate phases in sufficient quantities in marine sediments has led oceanographers to consider different approaches. The current models for seawater composition emphasize the dominant role played by the balance between the various inputs and outputs from the ocean. Mass balance calculations have become more important than solubility relationships in explaining oceanic chemistry. The difference between the equilibrium and mass balance points of view is not just a matter of mathematical and chemical formalism. In the equilibrium case, one would expect a very constant composition of the ocean and its sediments over geological time. In the other case, historical variations in the rates of input and removal should be reflected by changes in ocean composition and may be preserved in the sedimentary record. Models that emphasize the role of kinetic and material balance considerations are called kinetic models of seawater. This reasoning was pulled together by Broecker (1971) in a paper called "A kinetic model for the chemical composition of sea water."... 

Degens, E. T. and Mopper, K. (1976). Factors controlling the distribution and early diagenesis of organic material in marine sediments. In "Chemical Oceanography" (J. P. Riley, ed.), Vol. 6, pp. 59-113. Academic Press, New York. 

Ruttenberg, K. C. (1992). Development of a sequential extraction method for different forms of phosphorus in marine sediments. Limnol. Oceanogr. 37, 1460-1482. 

King JK, JE Kostka, ME Frischer, FM Saunders (2000) Sulfate-reducing bacteria methylate mercury at variable rates in pure culture and in marine sediments. Appl Environ Microbiol 66 2430-2437. 

Bauer JE, DG Capone (1988) Effects of co-occurring aromatic hydrocarbons on degradation of individual polycyclic aromatic hydrocarbons in marine sediment slurries. Appl Environ Microbiol 54 1649-1655. 

King GM (1984) Metabolism of trimethylamine, choline and glycine betaine by sulfate-reducing and metha-nogenic bacteria in marine sediments. Appl Environ Microbiol 48 719-725. 

Quensen JF, SA Mueller, MK Jain, JM Tiedje (1998) Reductive dechlorination of DDE to DDMU in marine sediment microcosms. Science 280 722-724. 

The ore fluids responsible for epithermal base-metal vein-type deposits were generated predominantly by meteoric water-rock interaction at elevated temperatures (200-350°C). Fossil seawater in marine sediments was also involved in the ore fluids responsible for this type of deposits. Epithermal precious metal ore fluids were generated by meteoric water-rock interaction at 150-250°C. Small amounts of seawater sulfate were involved in the ore fluids responsible for epithermal precious metal vein-type deposits occurring in Green tuff region (submarine volcanic and sedimentary rocks). 

Schantz MM, Benner BA Jr., Hays MJ, Kelly RW, Vocke RD Jr, Demiralp R, Greenberg RR, Schiller BS, LauenstEin GG, Wise SA (1995) Certification of standard reference material (SRM) 1941a, organics in marine sediment. Fresenius J Anal Chem 352 166-173. 

Horvat M, Mandic V, Liang L, Bloom NS, Padberg S, Lee Y.-H, Hintelmann H, and Benoit J (1994) Certification of methylmercury compounds concentration in marine sediment reference material, IAEA-356. Appl Organomet Chem 8 533-540. 

Sim PG, Boyd RK, Gershey RM, Gueveemont R, Jamieson WD, Qdilliam MA, and Geegely RJ (1987) A comparison of chromatographic and chromatographic/mass spectrometric techniques for the determination of polycyclic aromatic hydrocarbons in marine sediments. Biomed Environ Mass Spectrosc 14 375-381. 

Shaw TJ, Francois R (1991) A fast and sensitive ICP-MS assay for the determination of °Th in marine sediments. Geochim Cosmochim Acta 55 2075-2078... 

Slowey NC, Henderson GM, Curry WB (1995) Direct dating of the last two sea-level highstands by measurements of U/Th in marine sediments from the Bahamas. EOS 76(46) 296-297 Slowey NC, Henderson GM, Curry WB (1996) Direct U-Th dating of marine sediments from the two most recent interglacial periods. Nature 383 242-244... 

Radium, like most other group II metals, is soluble in seawater. Formation of Ra and Ra by decay of Th in marine sediments leads to release of these nuclides from the sediment into the deep ocean. Lead, in contrast, is insoluble. It is found as a carbonate or dichloride species in seawater (Byrne 1981) and adheres to settling particles to be removed to the seafloor. 

Seawater ( " U/ U) is higher than secular equilibrium due to a-recoil on the continents and in marine sediments. The history of seawater ( " U/ U) may provide information about the history of weathering during the Pleistocene. 

If Vtii/Ptii = 1 then the accumulation of °Thxs in marine sediments would provide an assessment of their sedimentation rate. For instance, if Pm is N dpm m yr , and N dpm are found in the upper 1 cm of 1 m of seafloor, then the sedimentation rate must be lcmyr Sedimentation rate is an important variable in paleoceanographic reconstruction as it provides the timescale for the continuous record of environmental change recorded in marine sediments. Sedimentation rate is also a key geochemical variable as sediments are the major sink for most chemical species in the ocean. A tool allowing assessment of past sedimentation rates is therefore an appealing prospect. 

Ra is soluble and therefore tends to be released to deep waters when it is formed by °Th decay in marine sediments. Substrates which capture the resulting excess of Ra found in seawater can potentially be dated using the decay of this Ra excess ( Raxs). Unfortunately there is no stable isotope of Ra with which to normalize measured Ra values but the marine chemistry of Ba is sufficiently close to that of Ra that it can be used as a surrogate for a stable Ra isotope and seawater Ra/Ba ratios are constant throughout the oceans, except in the deep North Pacific (Chan et al. 1976). The half life of Ra is only 1600 years so Raxs/Ba chronology is limited to the Holocene but it nevertheless has potential for use in several regions. 

Yu E-F, Francois R, Bacon M (1996) Similar rates of modem and last-glacial ocean thermohaline circulation inferred from radiochemical data. Nature 379 689-694 Zheng Y, Anderson RF, van Geen A, Fleisher MQ (2002) Preservation of particulate non-lithogenic uranium in marine sediments. Geochim Cosmochim Acta 66(17) 3085-3092. 

Measured concentrations of Th and Pa in marine sediments consist of three components that scavenged from seawater that supported by U contained within lithogenic minerals and that produced by radioactive decay of authigenic U. Most of the proxies described in this paper make use of only the scavenged component. Measured °Th and Pa must therefore first be corrected for the presence of the other two... 

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