Effects of organic solvents on stable isotopic composition of otolith and abiogenic aragonite

Abstract

Otoliths are important proxies for climate change and ecological studies and are typically stored in glycerin or ethanol for preservation. This study is the first attempt to assess the isotopic effects of these preservatives on carbon and oxygen isotope ratios of otolith aragonite. Experimental tests from the 4th annulus of dried Pacific halibut otoliths were compared to samples from the same otoliths collected after 30day storage in either glycerin or ethanol. In addition, isotopic measurements of abiogenic pure aragonite samples soaked in glycerin, ethanol, acetone, dichlorom (DCM), and methanol were compared to the initial values following the same protocol. No δ18O effect was observed for otoliths stored in glycerin or ethanol; and no isotopic effects (both δ18O and δ13C) were observed for abiogenic pure aragonite stored in the five organic solvents commonly used in geochemical laboratories. Although there was a significant but very small difference in carbon isotope ratios of halibut otoliths, the shift was of a barely measureable magnitude and the statistically significant difference only in δ13C values may result from the inhomogeneous composition and structure of otoliths. Thus we concluded that there was no isotopic exchange during organic solvent storage or preservative interference in the isotope ratio measurements.