Chemical Residence Time Research Articles

The thorium isotope content of ocean water

232Th concentrations of surface and deep Pacific Ocean waters are 0.01–0.02 dpm/1000 kg (60 pgm/kg). The 230Th activity is 0.03–0.13 dpm/1000 kg in surface waters and 0.3–2.7 dpm/1000 kg in deep waters. Chemical residence times based on in situ production from parent isotopes are about the same for 230Th and 228Th in surface waters (1–5 years) but are ten times greater for 230Th in deep waters (10–100 years). Apparently there are additional sources of 230Th into deep waters. At MANOP site S manganese nodule tops are enriched in Th isotopes by adsorption of Th from seawater and not by incorporation of Th-rich particulates.

Thermodynamic, kinetic, and extrathermodynamic considerations in the development of equilibrium models for aquatic systems

Thermodynamic and kinetic criteria are examined for the general application of equilibrium models to dynamic natural waters. The hypolimnion of a dimictic lake is used as a specific example. The majority of chemical reactions given consideration in equilibrium models are shown to be kinetically rapid in comparison to the chemical residence times in hypolimnetic waters. Extrathermodynamic relationships are explored as a method for extrapolating kinetic and thermodynamic constants from a limited set of experimental data.