Clumped isotopes

The new clumped-isotope (A47) carbonate thermometer, expressed as A47, offers an independent and potentially very powerful approach to paleoelevation reconstruction. In contrast to the use of 8180 values, nothing need be known about the isotopic composition of water from which carbonate grew in order to estimate of temperature of carbonate formation from A47 values. Using assumed temperature lapse rates with elevation, paleoelevations can thereby be reconstructed. 

PALEO-ELEVATION ESTIMATES USING CARBONATE CLUMPED ISOTOPE PALEOTHERMOMETRY... 

Carbonate clumped isotope thermometry is based on the temperature dependence of the abundances of bonds between 13C and lsO in carbonate minerals. This temperature sensitivity stems from the fact that isotope exchange reactions such as ... 

Figure 11. Data documenting the calibration of the carbonate clumped-isotope thermometer for inorganic calcite grown in the laboratory (filled circles) and aragonitic corals grown in nature at known temperatures (an example of one of several biogenic materials we have also calibrated unfilled symbols). The large, gray circle shows the result of analyses of a modern soil carbonate collected from the Bolivian Altiplano plateau. The horizontal position of this data point is based on the mean annual surface temperature near the site of collection between 2004 and the present.

Figure 12. Apparent growth temperatures for various Altiplano carbonates based on clumped isotope thermometry, plotted as a function of estimated maximum burial depth. Symbols discriminate among soil carbonates from sections near Callapa, Corque and Salla and lacustrine carbonates from near Tambo Tambillo, as indicated by the legend. The heavy solid line indicates an estimated burial geotherm, assuming a surface temperature of 20 °C and a gradient of 30 °C per km. The dashed lines define a 10° offset from this trend, which we consider a reasonable estimate of its uncertainty. Carbonates deposited within the last 28.5 Ma and buried to 5000 meters or less exhibit no systematic relationship between apparent temperature and burial depth, and show no evidence for pervasive resetting of deeply buried samples. Error bars are la (when not visible, these are approximately the size of the plotted symbol).

Came R, Veizer J, Eiler JM (2007) Surface temperatures of the Paleozoic ocean based on clumped isotope thermometry. Nature (in press)... 

Precollapse cloud cores are composed of cold molecular gas with ternperamres in the range 7 -15 K, and with gas densities —10 -10 mol cm (Figure 1). Some clouds may be denser yet, but this is hard to determine because of the limited density ranges for which suitable molecular tracers are abundant (typically isotopes of carbon monoxide and ammonia). Masses of these clouds range from roughly a solar mass to thousands of solar masses, with the distribution of clump masses fitting a power-law such that most of the clumps are of low mass, as is also true of stars in general. The cloud properties described below are used to constrain the initial conditions for hydrodynamic models of the collapse of cloud cores. 

---