Climatic dependence of stable carbon and oxygen isotope signals recorded in speleothems: From soil water to speleothem calcite

Abstract Understanding the relationship between stable isotope signals recorded in speleothems (δ 13 C and δ 18 O) and the isotopic composition of the carbonate species in the soil water is of great importance for their interpretation in terms of past climate variability. Here the evolution of the carbon isotope composition of soil water on its way down to the cave during dissolution of limestone is studied for both closed and open-closed conditions with respect to CO 2 . The water entering the cave flows as a thin film towards the drip site. CO 2 degasses from this film within approx. 10 s by molecular diffusion. Subsequently, chemical and isotopic equilibrium is established on a time scal…

Chemical evolution of dissolved inorganic carbon species flowing in thin water films and its implications for (rapid) degassing of CO2 during speleothem growth

Abstract Rapid degassing of CO2 from a thin film of drip water on the surface of stalagmites is often considered to have a large effect on both speleothem growth and stable isotope values and is offered as an explanation for higher δ13C and δ18O values than expected under conditions of stable isotope equilibrium. However, the time constant for degassing of CO2 from the solution only depends on film thickness and the coefficient of molecular diffusion for CO2. Thus, for thin films, the time for degassing of CO2 is much shorter than the time for subsequent equilibration of the dissolved carbon species and precipitation of CaCO3. In this context, degassing of CO2 is always fast. Here we presen…

Conformational substates of the Fe2+-His F8 linkage in deoxymyoglobin and hemoglobin probed in parallel by the Raman band of the Fe-His stretching vibration and the near-infrared absorption band III

Vibrational analysis of Ni(II)- and Cu(II)-octamethylchlorin by polarized resonance Raman and Fourier transform infrared spectroscopy

We measured the polarized resonance Raman spectra of Cu(II)-2,2,7,8,12,13,17,18-octamethylchlorin in CS2 at various excitation wavenumbers in a spectral region covering the Qy, Qx and Bx optical absorption bands. Additionally, we measured the FTIR-Raman spectrum of the highly overcrowded spectral region between 1300 and 1450 cm−1. The spectral decomposition was carried out by a self-consistent global fit to all spectra obtained. The thus identified Raman and IR lines were assigned by comparison with the resonance Raman spectra of Cu(II)-octaethylporphyrin, by utilizing their depolarization ratio dispersions and by a normal mode analysis. The latter was based on a modified transferable molec…

Conformational Properties of Nickel(II) Octaethylporphyrin in Solution. 2. A Low-Temperature Optical Absorption Spectroscopy Study

We have measured the absorption spectrum of Ni(II) octaethylporphyrin in CH2Cl2 and in a 50% v/v isopentane/ethyl ether mixture as a function of temperature between 150 and 300 K and 40 and 300 K, respectively. The Soret band can be decomposed into two subbands whose frequencies differ by 220 cm-1. By analogy with resonance Raman results (Jentzen et al. J. Phys. Chem. 1996, 100, 14184−14191 (preceding paper)), we attribute the low-frequency subband to a conformer with a nonplanar macrocycle structure, whereas the high-frequency subband is interpreted as resulting from a planar conformer. The subbands' intensity ratios exhibit a solvent-dependent van't Hoff behavior between 300 and 160 K. Cr…

Processes affecting the stable isotope composition of calcite during precipitation on the surface of stalagmites: Laboratory experiments investigating the isotope exchange between DIC in the solution layer on top of a speleothem and the CO2 of the cave atmosphere

Abstract We present a theoretical derivation of the exchange time, τex, needed to establish isotopic equilibrium between atmospheric CO2 in a cave and HCO3− dissolved in a thin water film covering the surface of a speleothem. The result is τ ex = τ red ex · [ HCO 3 - ] K H · p CO 2 cave , where τ red ex depends on the depth, a, of the water film and on temperature. [ HCO 3 - ] is the concentration of bicarbonate, p CO 2 cave the partial pressure of CO2, and KH is Henry’s constant. To test the theory we prepared stagnant or flowing thin films of a NaHCO3 solution and exposed them at 20 °C to an CO2 containing atmosphere of p CO 2 500, 12,500, or 25,000 ppmV and defined isotope composition. T…