Fossil fish teeth as proxies for seawater Sr and Nd isotopes

We analyzed Nd and Sr isotopic compositions of Neogene fossil fish teeth fr om two sites in the Pacific in order to determine the effect of cleaning pr otocols and burial diagenesis on the preservation of seawater isotopic valu es. Sr is incorporated into the teeth at the time of growth; thus Sr isotop es are potentially valuable for chemostratigraphy. Nd isotopes are potentia l conservative tracers of paleocirculation; however, Nd is incorporated pos t-mortem, and may record diagenetic pore waters rather than seawater. We ev aluated samples from two sites (site 807A, Ontong Java Plateau and site 786 A, Izu-Bonin Are) that were exposed to similar bottom waters, but have dist inct lithologies and pore water chemistries. The Sr isotopic values of the fish teeth appear to accurately reflect conte mporaneous seawater at both sites. The excellent correlation between the Nd isotopic values of teeth from the two sites suggests that the Nd is incorp orated while the teeth are in chemical equilibrium with seawater, and that the signal is preserved over geologic timescales and subsequent burial. The se data also corroborate paleoseawater Nd isotopic compositions derived fro m Pacific ferromanganese crusts that were recovered from similar water dept hs (Ling et al., 1997). This corroboration strongly suggests that both mate rials preserve seawater Nd isotope values. Variations in Pacific deepwater epsilon(Nd) values are consistent with predictions for the shearing of the Isthmus of Panama and the subsequent initiation of nonradiogenic North Atla ntic Deep Water that entered the Pacific via the Antarctic Circumpolar Curr ent. Copyright (C) 2000 Elsevier Science Ltd.