Isotope ratio in sediments

Estimate of global temperature based on proxy data such as tree rings and isotope ratios in sediments and ice cores. The 1990s was the warmest decade in 2000 years. [From M. E Mam and P D. Jones,"Global Surface Temperatures Over the Past Two Millennia," Geophys. Res. Lett. 2003,30.1820.]... 

Moor, H.C., Schaller, T., and Sturm, M. (1996) Recent changes in stable lead isotope ratios in sediments of Lake Zug, Switzerland. Environ. Sci. Technol., 30, 2928-2933. 

High -precision measurement of mercury isotope ratios in sediments using cold vapor generation multicollector inductively coupled plasma mass spectrometry. Anal. Bioanal. Chem., 384, 1470-1478. 

The concept for a marine paleoredox proxy based on variations in the U isotope ratio in sediments is very similar to the Mo isotope paleoredox proxy described earlier in this chapter. Since incorporation of U in oxidizing sediments such as ferromanganese crusts results in preferential removal of isotopically light U, and incorporation of U in reducing sediments results in preferential removal of isotopically heavy U, changes in the relative proportions of these two sinks over time should drive systematic shifts in the isotopic composition of U in seawater. In turn, these temporal shifts in the isotopic composition of seawater should be manifested as vertical fluctuations in in the sedimentary record. Excursions in the sedimentary record towards lighter values of (in any of these... 

Zheng, (. and Yamada, M. (2006) Determination of U isotope ratios in sediments using ICP-QMS after sample deanup with anion-exchange and extraction chromatography. 

This equation is particularly useful to derive apparent estuarine water mass ages (Fig. 6) because the term /em is removed. Using ( Ra/ " Ra) isotope ratios in this manner is based on the assumption that the initial ( Ra/ " Ra) activity ratio must remain constant. This conclusion is reasonable as the long-lived parent isotopes ( Pa and Th) have relatively constant activity ratios in sediments, and the intermediate Th isotopes ( Th and Th) are scavenged efficiently in the near-shore water column. The utility of Ra as... 

Hirao Y, Mabuchi H, Fukuda E, et al. 1986. Lead isotope ratios in Tokyo Bay sediments and the implications in the lead consumption of Japanese industries. Geochemical Journal 20 1-15. 

Yang, H. and Huang, Y. (2003) Preservation of lipid hydrogen isotope ratios in Miocene lacustrine sediments and plant fossils at Clarkia, northern Idaho, USA. Organic Geochemistry 34, 413. 

Longinelli, A. (1995). Stable isotope ratios in phosphate from mammal bone and tooth as climatic indicators. In Problems of Stable Isotopes in Tree-rings, Lake Sediments and Peat-bogs as Climatic Evidence for the Holocene, ed. Frenzel, B., European Science Foundation, Strasbourg, pp. 57-70. 

Hagiwara (2000) completed a reconnaissance survey of Se isotope variation in marine sediments and sedimentary rocks (Table 4). The most important observation was a lack of strong enrichment in lighter isotopes in most shale samples and three Black Sea sediments. It appears that near-surface alteration has altered Se isotope ratios in some cases. All of the Phosphoria formation samples were probably altered by deep groundwater or hydrothermal... 

Hagiwara Y (2000) Selenium isotope ratios in marine sediments and algae. A reconnaissance study. M.S. 

O, H, C, S, and N isotope compositions of mantle-derived rocks are substantially more variable than expected from the small fractionations at high temperatures. The most plausible process that may result in variable isotope ratios in the mantle is the input of subducted oceanic crust, and less frequent of continental crust, into some portions of the mantle. Because different parts of subducted slabs have different isotopic compositions, the released fluids may also differ in the O, H, C, and S isotope composition. In this context, the process of mantle metasomatism is of special significance. Metasomatic fluids rich in Fe +, Ti, K, TREE, P, and other large ion lithophile (LIE) elements tend to react with peridotite mantle and form secondary micas, amphiboles and other accessory minerals. The origin of metasomatic fluids is likely to be either (1) exsolved fluids from an ascending magma or (2) fluids or melts derived from subducted, hydrothermally altered crust and its overlying sediments. 

In some deep-sea sediment columns, records of IDP fall-out can be traced back to several ten million years with the help of extraterrestrial He as a tracer. Such a remarkable example was reported by Farley (1995). Farley measured 3He/4He ratios in a pelagic sediment core drilled from the central North Pacific. The core is thought to carry a nearly complete sedimentation record to 72Ma. Figure 5.6 shows records of the He concentration and the isotopic ratio in the drilled core. 

The first neodymium-isotopic analyses aimed at characterizing the oceans closely followed the initial development of neodymium isotopes as a chronometer and tracer (Richard et al., 1976 DePaolo and Wasserburg, 1976a O Nions et al., 1977). O Nions et al. (1978) was the first to report neodymium (along with lead and strontium) isotopes in manganese nodules and hydrothermal sediments. They confirmed the distinction between continental and mantle provenances of lead in hydrogenous and hydrothermal manganese sediments, respectively. Consistent with the previous studies, they found that strontium in these deposits is derived from seawater. All of the neodymium-isotope ratios in their samples from the Pacific were similar and lower than the bulk... 

Passage values (Figure 7). This may indicate a source of neodymium with high isotope ratios in the South Atlantic. However, it is premature to conclude that deep South Atlantic neodymium-isotope ratios overstep the Southern Ocean values, for the following reasons. The maxima for all of the deep South Atlantic waters are between SNd = 7 to —9, more variable than presently available data from the Drake Passage but still quite similar. This range is also similar to circumpolar Fe-Mn sediments (Albare(c)de et al., 1997). Depth profiles from the western Indian Ocean near southern Africa are similar to the South Atlantic and Drake Passage, but like the South... 

The basin margins are characterized by calcite and minor dolomite cements, many of which which formed in isotopically light brackish or meteoric water at low temperature. In general, calcites did not form near the sediment-water interface, but during shallow burial. On the east side of the basin these cements are characterized by widely varying 5 Cpdb values (+20 to -30) compared with central basin cements (+5 to -10). Sr isotopic ratios in cements are lower than the marine depositional waters on the east side of the basin, but are higher than expected for depositional waters on the west side. 

The stable carbon isotope signal preserved in benthic foraminiferal carbonate tests reflects global ocean circulation and organic carbon fluxes. It is also subject to local influences, notably gradients in the isotope ratios of sediment pore-waters ( microhabitat effect ), and vital effects possibly related to the incorporation of metabolic carbon into the shell material (McCorkle et al. 1990 Mackensen Bickert 1999 Schmiedl et al. 2004). Mackensen et al. (1993) recogiuzed a ph)4odetritus effect whereby deviations in 8 C... 

Peters KE, Sweeney RE, Kaplan IR (1978) Correlation of carbon and nitrogen stable isotope ratios in sedimentary organic matter. Limnol Ocean 23 598-604 Plank T, Langmnir CH (1998) The chemical composition of subducting sediment and its consequences for the crast and mantle. Chem Geol 145 325-394... 

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