Chemical weathering of continental rocks by rivers is the Earth's main method of removing atmospheric CO2, and is therefore an important natural climate controlling mechanism. The formula below demonstrates that when a Ca or Mg silicate rock is dissolved in water, atmospheric CO2 is also dissolved. This is then transported through the rivers to the oceans, where some of it is locked up as a carbonate on the sea floor:
(Ca,Mg)SiO3 + 2CO2(atmos.) + 2H2O => (Ca,Mg)CO3 + SiO2 + CO2(atmos.) + 2H2O
It therefore is important to understand what controls chemical weathering, in order to understand how long-term climate change operates. One of the likely controls in temperature, in that a warm climate would increase the speed of the weathering reactions. This would remove more CO2, eventually allowing the climate to cool. Equally low temperatures would inhibit weathering, allowing CO2 to build up, thus warming the atmosphere. This would mean that chemical weathering is the process that has maintained the Earth habitable for life for billions of years.
Our research involves using the isotopes of metals such as Li, Mg, Ca and Si to study these weathering processes. All these isotope systems are affected by different aspect of weathering. We are using these systems to examine modern weathering in different climatic conditions, such as rivers and soils in Iceland, the Azores, Costa Rica and Australia. We are also applying them to records of ocean chemistry (such as limestone) through large climate changes in the past (e.g. the Permo-Triassic) to understand how weathering, climate change and mass extinctions link.
We are also using these isotopes to examine the chemical consequences of speeding up weathering to artificially sequester CO2.
- Examining modern weathering processes in a glaciated terrain in Iceland, using Li, Mg and U-series isotopes.
- Comparing weathering processes in Iceland with temperate (Azores) and tropical (Costa Rica) climates to examine the effect of temperature and vegetation.
- Groundwater weathering processes in Australia, to determine the contribution of groundwater to global weathering and CO2 sequestration.
- Determining the weathering response to past changes in climatic conditions, using Li isotopes. Time periods examined include the end-Ordovician and the Permo-Triassic, which respectively represent extreme global cooling and warming periods.