The Open University Uranium-Series Laboratory hydrology

Oxygenated recharge waters have extremely high U/Th and high (²³⁰Th/²³²Th), but both decrease with time under reducing conditions. Combined with other trace element characteristics and data from flow models, U-series isotopes may be used to determine residence times in aquifers (Osmond and Cowart, 1992). This approach has potentially important applications for drinking water extraction, and elsewhere for understanding the likely effects of discharges from the nuclear and other industries.

U-series data (together with δ⁶Li) have been used successfully to assess silicate weathering rates in only a few climate zones and there is great scope for extension. Moreover, there is no consensus on the paleo-variations of the controlling factors of silicate weathering rates.

Hydrothermal systems and possible analogues for radioactive waste.
Another area of where U-series isotope analyses have significant potential is in the investigation of natural hydrothermal systems. High temperature geothermal fields are found at a number of localities in volcanically and seismically active areas on the Earth's surface, and represent 'natural laboratories' where the reactions which take place between high temperature fluids and silicate rock may be investigated at first hand. The behaviour of naturally occurring radioactive elements in high-temperature fluids may provide an analogue for radioactive waste studies, and the measurement of natural short-lived isotopes such as ²³⁴U, ²³⁰Th, ²²⁸Ra and ²²⁶Ra allows constraints to be placed on the time scales of fluid movement. Along the Earth's submarine mid-ocean ridges, hydrothermal systems are ubiquitous and they have a profound influence not only on the basalt erupted there but also on the chemistry of the oceans, and of sulphide formation (You and Bickle, 1998). In the active volcanic geothermal fields of the Taupo area in New Zealand, the rates of mass transfer have been investigated by documenting the change in Sr isotopes with height in the altered volcanic rocks, and by dating the different generations of hydrothermal carbonates using U-Th isotopes (Grimes et al., 1998).