Factors determining delta C-13 and delta O-18 fractionation in aragonitic otoliths of marine fish

Fish otoliths are aragonitic accretions located within the inner ear of teleost fish. The acellular nature of otoliths, along with taxon-specific shapes, chronological growth increments, and abundance in the fossil record suggest that the stable isotope chemistry of these structures may be unique recorders of environmental conditions experienced by fish in both modern and ancient water masses. To assess the factors determining delta(13)C and delta(18)O fractionation in fish otoliths, we reared Atlantic croaker (Micropogonias undulatus) larvae under controlled environmental conditions. Metabolic effects apparently generated large isotopic disequilibria in the delta(13)C Values of M. undulatus otoliths. We found evidence of a negative regression between delta(13)C(carbonate)-delta(13)C(water) (Delta(13)C) and temperature: Delta(13)C = -1.78 - 0.18 T degrees C However, this relationship was aliased to a degree by a positive correlation between Delta(13)C and somatic growth and otolith precipitation rates. Oxygen isotopes were deposited close to equilibrium with the ambient water. The relationship between temperature and the O-18/O-16 fractionation factor (alpha)) was determined empirically to be: 1000 ln alpha = 18.56 (10(3) T K-1) - 32.54 The fractionation factor was not affected by either otolith precipitation or fish growth rates. Reconstruction of water temperature histories should, therefore, be possible from the delta(18)O values of M. undulatus otoliths with a precision of 1 degrees C, providing the delta(18)O of the ambient water can be estimated. Copyright (C) 1997 Elsevier Science Ltd.