Prof. Edward Tipper

The inhabitable surface of the Earth is shaped by many processes, tectonics, erosion, chemical weathering and life. My research interests concentrate on the links between the hydrosphere, atmosphere and lithosphere. How do chemical reactions at the Earth's surface mediate the chemistry of the atmosphere and seawater over geological time? How are these reactions influenced by rock composition and how do these reactions influence rock composition? To answer these geological questions I use geochemical methods, exploiting small variations in isotope ratios. Until the last decade it was not possible to measure these with sufficient precision to address geological questions that interest me. I have been involved in developing Mg and Ca isotope tracers as geochemical tools to investigate the important role of chemical weathering to geochemical budgets.  I am involved in a series of major fieldwork expeditions. 

I am currently involved in several major research projects funded by NERC:

1.   Carbon transfer in the Himalaya by chemical weathering in the wake of the April 2015 Nepal Earthquakes:   Chemical weathering regulates Earth’s carbon cycle and hence global climate over geological timescales. Ca and Mg from silicate minerals are released to the solute phase during chemical weathering. In the Himalaya, weatherable material is mainly supplied by landslides.  Thousands of landslides were triggered by the 2015 earthquakes and this research seeks to understand the role of tectonics in controlling carbon transfer at an orogenic scale.  We have been collecting samples in the aftermath of the earthquakes and continue to collect water and sediment samples.  The objective of this project is to quantify the impact of this ∼100 year event on inorganic and organic carbon fluxes exported from this part of Nepal. This will determine the impact of such major events on the chemical fluxes thought to moderate long-term climate change. 
2. The key to quantifying chemical weathering intensity: clay stable isotope fractionation factors:  A fundamental aspect of chemical weathering is the formation of new solid phases, mainly clays in the soil environment or "critical zone". The type and amount of clay produced depends on several variables, amongst which climatic parameters (temperature, hydrological intensity) dominate. The development of novel stable isotope ratios over the past decade offers a different but complementary view of the carbon cycle, with magnesium, silicon and lithium  isotope ratios among the most promising tracers of weathering and oceanic budgets. A wealth of field data now suggests that Mg, Li and Si isotope ratios (and by implication the mass budgets of these elements) are strongly influenced by the formation of clay minerals both in the marine and terrestrial realm. However, there are almost no determinations of isotopic fractionation factors between solutes and clay and these studies only consider one type of clay. In the absence of known fractionation factors, the field data can at best provide a qualitative constraint, but at worst the interpretations may be incorrect.  We are in the process of determining the isotopic fractionation factors for Mg and Li isotopes for the most common types of clay using novel techniques and state-of-the art material characterisation techniques in collaboration with Nick Tosca at the University of Oxford.
3. Earth's weathering reactor: carbon source or sink over short and long time-scales?  We are working on  three of the largest rivers in the world as case studies for carbon transport, the Irrawaddy, Salween and Mekong from SE Asia. Combined, these rivers transport about 14% of the global total riverine flux of carbon, or about half the UK's carbon emissions, but there is so little work on these basins that their impact is largely unknown. Does the transfer of carbon end up releasing carbon dioxide, or do these river basins act as a sink for carbon? We propose to constrain the modern carbon budgets in these basins by using a series of isotopes, that will tell us if ancient carbon is being released from rocks, or whether modern carbon derived from the atmosphere or biosphere is being consumed.
4. The impact of cation exchange to estimates of chemical weathering fluxes: Estimates of carbon consumption by silicate weathering could be wrong by up to 80% because of cation exchange processes that have not been considered in estimates of carbon consumption by silicate weathering. This is because Ca fluxes from silicate weathering are typically based on Na fluxes, assuming that Na has conservative behaviour. It has been suggested that Na and Ca are strongly influenced by cation exchange processes, significantly biasing the quantification of silicate weathering.  We are using Li and and Mg isotope ratios to better quantify the role of cation exchange on controlling chemical weathering fluxes in a series of large rover basins from across the world.