Dating sediment

The environmental occurrence of polycyclic aromatic hydrocarbons is mainly associated with dispersion of oil products and with various types of combustion. For these chemicals a kind of pre-industrial background exists, due to forest fires or to domestic wood burning. The sediments of the deepest strata were certainly deposited in the nineteenth century, when no significant industrial activities had been initiated. The ratio between PAH concentrations found in the sediments dated to this century, and the deepest ones, vary from 1.7 to 30, increasing from the beginning of the... 

In order to provide AMS analyses to the broad ocean sciences research community, the National Ocean Sciences Accelerator Mass Spectrometry Facility (NOSAMS) was established at Woods Hole Oceanographic Institution (Massachusetts) in 1989. Studies performed there include identification of sources of carbon-bearing materials in the water column and sediment, dating of sedimentary samples, investigations of paleocirculation patterns (e.g., from observations of differences in 14C relative abundances in planktonic and benthic foraminifera, and coral cores and cross sections), as well as studies of modern oceanic carbon cycling and circulation. In fact, much that is known about advective and diffusive processes in the ocean comes from measurements of chemical tracers, such as 14C, rather than from direct measurements of water mass flow. 

Fig. 2. CO2 concentrations (ppmv) and 5 O (%o) in air trapped in an ice-core (Dye 3) from Greenland. The tentative time marks at 10 and 13,000 years BP are suggested by comparison with European lake sediments dated by caibon 14. Also shown is the Be/ concentration (10 atoms per g of ice) in the core. The approximate parallelism with the 6 O and the carbon dioxide concentration indicates that when the climate became colder the rate of snowfall on Greenland diminished. (From Neftel et d., 1982).

Bada J. L., Luyendyk B. P., and Maynard J. B. (1970) Marine sediments dating by the racemization of amino acids. Science 170, 730-732. 

The same isotopes that are useful tracers of adsorption in the water column are ideal for determining sediment accumulation rates because they are chemically separated from their radioactive parents in the overlying water column. Radionuclides commonly used for sediment dating include °Th (ty2= 75 200y), Pa (ti/ = 32 500 y) and °Pb U/ , = 22.3 y). Given the need to match... 

Prescott, J.R. Robinson, G.B. (1997) Sediment dating by luminescence a review. Radiation Measurement 27, 893-922. 

Norton, S. A. C. T. Hess, 1980. Atmospheric deposition in Norway during the last 300 years as recorded in SNSF lake sediments. 1. Sediment dating and chemical stratigraphy. Proc. Int. Conf. Ecol. Impact Acid Precip. Norway 1980, SNSF Project. 

Keywords atmospheric deposition combustion products industrial pollutants inorganic ash spheres sediment dating spheroidal carbonaceous particles... 

There are currently three main features employed in SCP sediment dating. These are the start of the particle record, the rapid increase in concentration, and the concentration peak. Some regional variability occurs and these features must be calibrated to independently-derived dates (e.g. annual varves " Pb chronologies) before application to sediment profiles from other lakes. In lakes with very slow sediment accumulation, the maximum concentration may be at the surface. Other dates may be attributable by using cumulative percentage profiles, or possibly by SCP fuel-type characterisation. 

Rose, N. L., 2000. Carbynet. On-line sediment dating information. http //www.geog.ucl.ac.uk/ecrc/carbynet/... 

These latter industries seemed unwilling, at the time, to contribute to the debate or the research. It must be remembered that the flame retardant industry is a relatively young one, established in the early 1970s, and the BSEF highlights a report published in 1992, which provides evidence of PBDEs in sediment dating back to the 1940s. 

An important application of radioactivity in science is its use to determine the ages of human artifacts and of rocks and sediments. Dating techniques rely on naturally occurring radionuclides. Archaeologists use carbon dating to determine the age of human artifacts. Geologists use long-lived radioactive materials such as uranium and thorium to determine the age of rocks and Earth. 

The U.S. ERA currently supports and maintains the WASP model, including various versions from 4 through 7 (Ambrose et al., 1988 1993 Wool et al., 2001). The first ERA public domain WASP applications to examine toxic chemicals in receiving waters and sediments date back to late 1980s with evaluations of volatile organics in the Delaware Estuary (Ambrose, 1987) and heavy metals in the Deep River, North Carolina (JRB, 1984). As a public domain model, various enhancements of the WASP model have been made over the years in order to address site-specific needs and improve on the standard transport and kinetic formulations to simulate a variety of toxics, especially hydrophobic organic chemicals (HOCs) and metals. Several modified versions of the WASP model incorporate settling and resuspension functions that are not available in the EPA-supported model. The WASP model discussion... 

A further point of interest in the East China Sea stratigraphy is the initial occurrenee of phytoliths at 13,900 years ago and then their absence from the sediments dated between 13,000 and 10,000 years ago. This latter period was characterized by a return to relatively cold conditions following rapid warming as the last ice age ended. This climatic deterioration may have resulted in an abandonment of rice cultivation which was resumed after 10,000 years before the present. 

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