Getting our teeth into climate models
Models of the Earth's future climate rely heavily on accurate reconstructions of previous climates to confirm the predictions being made. Especially important are predictions of past sea surface temperatures as they are a critical factor of the Earth's climatic system. The composition of different oxygen isotopes in minerals produced by marine organisms and preserved in fossils can be used as measurements for reconstructing past climate conditions. One such 'proxy' for ancient seawater is shark teeth, which contain geochemical signals (including oxygen isotopes) trapped in their apatite phosphate. A major advantage of apatite phosphate is that it changes very rapidly in early enzyme reactions. However, it changes extremely slowly in inorganic systems over geological timescales preserving the oxygen isotopic ratio at the time of formation. Fossil shark teeth make a good proxy for reconstructing ancient environments because of their relative abundance and the geochemical stability of their tissues. Data from the fossilised teeth can then be compared with the teeth of modern sharks. The EU-funded 'Vertebrate isotopes and the environment' (VISE) project tested the reliability of using apatites in fossil shark teeth as a proxy. This was done by comparing them with the analysis of shed teeth from living sharks kept in marine aquaria under controlled conditions for water temperature and composition. Data from the VISE project will form a critical test regarding the use and limitations of using vertebrate apatite proxies for reconstructing past climates.
