EVALUATION OF BIOMEDIATED FRACTIONATION OF 13C AND 18O ISOTOPES: AQUATIC GASTROPOD PHYSIOLOGY AND MINERALOGY

Stable carbon and oxygen isotopes (13C and 18O) are widely used paleoenvironmental proxies within aquatic carbonate systems. This study characterizes fractionation from the incorporation of 13C and 18O from water into gastropod shells from spring locations in the West Desert region of Utah. Water-to-shell differences of stable isotopes between site, species (of which there were six), intrashell variations, and species physiology (gill and lung breathing) were measured. Water temperature, salinity, pH, and alkalinity were monitored over a four-year period at each of the locations and water isotope and major ion chemistry were characterized. Gastropod shells were isolated from the spring sediment and were cleaned using a combination of manual and chemical methods. The shells were separated by site and species then crushed into homogenized powders using a mortal and pestle. For some shells, intrashell transects were taken using a microdrill. Samples were analyzed for δ¹³C and δ¹⁸O at the SIRFER lab at the University of Utah. Thin sections were made and examined using microscopy for three of the species. The results demonstrate variations in isotopic fractionation between species, sites, and physiology. The intrashell variation had slight statistical significance indicating variation throughout the shells. This study contributes towards a larger study on the use of aquatic gastropod shells as paleoenvironmental proxies and helps to constrain stable isotope fractionation due to vital effects in physiology and mineralogy.