BIOAPATITE THERMOMETER IN THE MODERN WORLD

Reconstructing paleoclimates relies on temperature proxies. These proxies relate water temperature to trace elemental composition of biominerals, most commonly calcium carbonate. In the ocean, calcium carbonate can only exist above the carbonate compensation depth (CCD). Bioapatite is another common biomineral that may have potential for storing paleotemperatures and exists below the CCD. Fish teeth are made of bioapatite and reflect environmental water chemistry because fish are cold blooded. Bioapatite is a calcium phosphate mineral, in which strontium will replace calcium in trace amounts. This presentation investigates the hypothesis that Sr/Ca ratios of bioapatite will be higher in warmer water temperatures than in colder water temperatures. Here we show that preliminary Sr/Ca ratios of mosquitofish and king mackerel teeth reflect the temperature of water that the fish lived. Further, teeth and bones were extracted from 30 bluegill fish collected from the Tracy Fish Collection Facility. This work revealed that cold maceration time corresponds with fish size. Otoliths were found and the size of fish teeth correlates to the size of the fish. These 30 bluegills represent two different temperature groups and are roughly the same age. This study contributes refinement of methods for tooth and bone extraction as well as information about bluegill environment and history. The preliminary data supports the hypothesis of fish tooth trace elemental composition and water temperature. The method refinement and fish ecology findings enable further testing of this hypothesis. The development of a bioapatite temperature proxy will further paleoclimate research and open the door to a temperature proxy that is not reliant on calcium carbonates.