Diatom sediments

Evidence of the fall dump of giant diatoms. Sediment layers from (a) the Gulf of California dominated by cell walls of Stephanopyxis palmeriana (diameter <70 ji,m) (b) the Southern Ocean, showing a tangled mass of the rod-shaped species Thalassiothrix antarctica, which grows up to 4 mm in length. Source From Kemp, A. E. S., et al. (2000). Deep-Sea Research II, 47, 2129-2154. 

One method for measuring the temperature of the sea is to measure this ratio. Of course, if you were to do it now, you would take a thermometer and not a mass spectrometer. But how do you determine the temperature of the sea as it was 10,000 years ago The answer lies with tiny sea creatures called diatoms. These have shells made from calcium carbonate, itself derived from carbon dioxide in sea water. As the diatoms die, they fall to the sea floor and build a sediment of calcium carbonate. If a sample is taken from a layer of sediment 10,000 years old, the carbon dioxide can be released by addition of acid. If this carbon dioxide is put into a suitable mass spectrometer, the ratio of carbon isotopes can be measured accurately. From this value and the graph of solubilities of isotopic forms of carbon dioxide with temperature (Figure 46.5), a temperature can be extrapolated. This is the temperature of the sea during the time the diatoms were alive. To conduct such experiments in a significant manner, it is essential that the isotope abundance ratios be measured very accurately. 

An accompanyiag effect of eutrophication that is more readily observable ia Table 1 is a decrease ia siUca coaceatratioa ia Lake Oatario. Some decliae ia dissolved siUca appareatiy has occurred ia all of the lakes except Lake Superior. This decliae is brought about by the growth of diatoms, a species of aquatic microorganisms ia the upper layers of lake water that is widespread ia all types of water impouadmeats where the water is clear and exposed to the sun. The siUca is used by these microorganisms to form their skeletons and is later precipitated and becomes part of the bed sediment. 

Most commercial marine diatomite deposits exploit accumulations resulting from large blooms of diatoms that occurred ia the oceans during the Miocene geological epoch. Diatomite sediments older than the Jurassic period are rare in the fossil record. Commercial deposits of diatomite are accumulations of the fossil skeletons, which can occur in beds as thick as 900 m in some locations (5). Marine deposits must have been formed on the bottom of protected basins or other bodies of quiet water, undisturbed by strong currents, in an environment similar to the existing Santa Barbara Channel or Gulf of California (3,6). 

As noted already, intense submarine hydrothermal activity took place in the Japan Sea in 15-12 Ma, associated with Kuroko mineralization. However, it is uncertain that submarine hydrothermal activities associated with the Kuroko mineralization took place in the other periods from middle Miocene to present in the Japan Sea. Therefore, the geochemical features of sedimentary rocks which formed from the Japan Sea at these ages have been studied by the author because they are better indicator of age of hydrothermal activities than those of hydrothermally altered igneous rocks because the samples of continuous age of sedimentation are able to be collected and the ages are precisely determined based on microfossil data (foraminiferal, radioralian and diatom assemblages). 

Simoneit, B.R.T., Philip, R.P., Jeden, P.D. and Galimov, E.M. (1984) Organic geochemistry of Deep Sea Drilling Project sediments from the Gulf of California - Hydrothermal effects on unconsolidated diatomic ooze. Org. Geochem., 17, 173-205. 

Dickman, M. Fortescue, J. 1984. Rates of lake acidification inferred from sediment diatoms for eight lakes located north of Sudbury. Verhandlungen Internationale Vereinigung fuer Theoretische und Angewandte Limnologie, 22, 345-1356. 

Diatoms and the Scanning Electron Microscope Acid Treatment Method Hydrogen Peroxide Method Obtaining Diatom Specimens from Sediments Preparation of Attached Diatoms Preparing Cleaned Diatoms for Viewing on the Scanning Electron Microscope References... 

We have found the method described by Sullivan (11) extremely useful for extracting diatoms out of marine sediment deposits (see Fig. 3). Using the following technique, Sullivan (11) was able to identify new genera and species of diatoms. 

The bioavailability of selenium to a benthic deposit-feeding bivalve, Macoma balthica from particulate and dissolved phases was determined from AE data. The selenium concentration in the animals collected from San Francisco Bay was very close to that predicted by a model based on the laboratory AE studies of radiolabelled selenium from both particulate and solute sources. Uptake was found to be largely derived from particulate material [93]. The selenium occurs as selenite in the dissolved phase, and is taken up linearly with concentration. However, the particle-associated selenium as organoselenium and even elemental selenium is accumulated at much higher levels. The efficiency of uptake from the sediment of particulate radiolabelled selenium was 22%. This contrasts with an absorption efficiency of ca. 86% of organoselenium when this was fed as diatoms - the major food source of the clam. The experiments demonstrated the importance of particles in the uptake of pollutants and their transfer through the food web to molluscs, but the mode of assimilation was not discussed. 

Pontanen and Morris [8] compared the structure of humic acids from marine sediments and degraded diatoms by infrared and C13 and proton NMR spectroscopy. Samples of marine sediments taken from the Peru continental shelf were extracted with water, sodium hydroxide (0.05mol 1 J) and sodium pyrophosphate (0.05mol l-1) under an atmosphere of nitrogen and fractionated by ultrafiltration. Humic acids of molecular weight 300000 and above were examined. Diatoms were collected from... 

Sigman, D.M., M.A. Altabet, R. Francois, D.C. McCorkle, and G.-F. Gaillard. 1999. The isotopic composition of diatom-bound nitrogen in Southern Ocean sediments. 

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