| Summary: | The mid-Pliocene warm period (3.29-2.97 Ma) was a time broadly characterised by global warmth and high sea levels. It represents the last time in Earth history when the level of atmospheric CO2 was similar to today (~ 380 ppm) and as such, it may provide a model for future global warming. The Mean Annual Range of Temperature (MART) experienced by a bryozoan colony can be estimated utilising the inverse relationship between zooid size in cheilostome bryozoans and water temperature at the time of budding (O'Dea and Okamura, 2000a). In this study the technique is applied to Pliocene bryozoan material from the UK, US Coastal Plain, Florida and the Isthmus of Panama. Absolute temperatures have been reconstructed from stable isotopic analyses performed on bryozoans from a number of sites. This technique relies on the principle that the skeletal material is secreted in isotopic equilibrium with seawater. The lighter oxygen isotope, ¹⁶0, is preferentially incorporated into the skeleton during warmer temperatures therefore the ratio of ¹⁶0:¹⁸0 can act as a thermometer allowing temperature of the water at the time of skeleton formation to be inferred. Data from a range of latitudes provide information about shelf sea temperatures, and are found to be consistent with outputs from mid-Pliocene scenarios generated by numerical models of climate (General Circulation Models).
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