Magnesium is a major constituent in silicate and carbonate minerals, the hydrosphere and the biosphere. Magnesium is constantly cycled between these reservoirs. Since each of the major planetary reservoirs of magnesium has different magnesium isotope ratios, there is scope to use magnesium isotope ratios to trace 1) the processes that cycle magnesium at a spatial scale from the entire planet to microscopic and 2) the relative fluxes between these reservoirs. This review summarises some of the key motivations, successes and challenges facing the use of magnesium isotopes to construct a budget of seawater magnesium, present and past.
1. Introduction
2. What do Mg isotopes promise?
3. The modern oceanic budget system
4. Past records of seawater
5. Diagenesis: Not records of seawater at all?
6. Perspectives for the future
7. Key papers