VISE

Vertebrate isotopes and the environment

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 Obiettivo del progetto (Objective)

'Predictions of the impact of future climate change have to be grounded in a firm understanding of environmental change in the geological past. Proxies for the isotopic composition of past oceans are widely used to give an insight into their water chemistry and, by extension, the surface temperature of these oceans. Variations in the ratio of Oxygen 16:Oxygen 18 (δ18O) are the most widely utilized proxy for water temperature, and are typically derived from fossil hard tissues, with the δ18O of biogenic apatites such as that of fish teeth being considered to be the most robust. Nevertheless, the isotopic behaviour of fossil biogenic apatites in general, including the effects of diagenesis and other postmortem artefacts, is still not fully understood, which ultimately reflects a lack of primary and systematic study. This project tests the reliability of biogenic apatite δ18O in a controlled modern environment, utilizing the regularly shed teeth of sharks living in a contained body of water from which we can directly monitor variations in isotopic composition and also assess compositional variation due to species fractionation. This will also provide the basis for rigorous testing of the proposition that the isotopic geochemistry of marine vertebrate biogenic apatites are influenced by standard laboratory processing methods of fossil materials. Using evidence derived from these experimental studies, taxonomic variations in isotopic composition within phylogenetically distinct fossil vertebrates through documented intervals of palaeoclimatic change in the Palaeozoic will be evaluated. The results of this project will provide a critical and timely test of the use and limitations of vertebrate biogenic apatite proxies in the reconstruction of past climates. Our project will provide training to a promising Lithuanian researcher in experimental methods in isotope geochemistry within state of the art isotope laboratories and a unique integration of modern and fossil materials'

Introduzione (Teaser)

Shark teeth are helping scientists understand what the Earth's climate was like millions of years ago.

Descrizione progetto (Article)

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.