HERE TODAY, GONE TOMORROW: DISSOLUTION OF FOSSIL BONE UNDER A CHANGING CLIMATE

Fossils provide an important archive of past life, ecosystems, and environments. Like all rocks and minerals, fossils are susceptible to weathering and dissolution over time resulting in partial or total loss of fossil material and paleoenvironmental information. Fossil bone is a mixed mineral system composed primarily of calcium and phosphorus-bearing apatite minerals, with additional secondary minerals such as calcite, gypsum, and silicates also commonly present. The complex mineralogy of fossils makes thermodynamic prediction of dissolution rates challenging, and empirical studies of rates of fossil dissolution under different environmental conditions are lacking. Generating improved estimates of environmental impacts on fossil dissolution rates has direct implications for resource management and conservation efforts, and is particularly important in the face of changing climate. We performed a series of controlled experiments to quantify and characterize fossil dissolution when exposed to waters with variable pH (4, 5, 6), temperature (20 and 30°C), and pH buffered by addition of different acids (hydrochloric and acetic). These conditions were designed to reflect the impacts of modern climate change including increasingly acidic precipitation, higher temperatures, and enhanced organic acid production resulting from greening. Over 21 days, fossil loss occurred under all experiments with the greatest mass loss (up to 40%) observed with acetic acid buffered solutions at 20°C and pH 4. Overall, increased mass loss was observed with lower pH and in acetic acid buffered solutions with no change in mass loss found between temperatures. The fossil bones used in this experiment initially consisted of fluorapatite (36%), calcite (35%), and amorphous phases (29%). Fossil loss was primarily driven by loss of calcite in experiments with acetic acid buffered solutions, whereas loss of amorphous phases in experiments with hydrochloric acid buffered solutions dominated. These results demonstrate the complex interplay between fossil mineralogy and solution chemistry and their impact on fossil stability when exposed at Earth’s surface. Additionally, these results provide insight into differences in fossil stability across geographic regions and as a result of changing climates, which can be used to guide conservation and resource management decisions.