5. Conclusion
Our results demonstrate that SIMS is a powerful tool that can be used to generate accurate, multi-year Sr/Ca time series from altered fossils. As most coral proxies are impacted by diagenesis to some extent, the sampling and data processing strategies presented here serve as a “roadmap” for recovering accurate paleoenvironmental reconstructions from altered corals using a wide variety of micro-scale analytical techniques, e.g. SIMS-based oxygen isotopes or Mg/Ca using laser ablation ICP-MS. Given the sheer volume of analyses needed to overcome fine-scale heterogeneity in coral geochemistry (e.g. the 730 individual SIMS analyses presented here cost ~$15,000), microscale geochemical analyses are not practical in all circumstances. However, microscale analyses can and should be used to verify the accuracy of conventional, bulk Sr/Ca records from fossil corals, given that (i) no fossil coral is devoid of diagenesis, and (ii) even trace diagenesis can impart a significant artifact to coral Sr/Ca-based SST reconstructions, given the sensitivity of the coral Sr/Ca-SST relationship.
Acknowledgements
We’d like to thank Anne L. Cohen for providing laboratory resources and feedback that helped shape this work, and the phenomenal staff of the Northeast National Ion Microprobe Facility, including Nobumichi Shimizu, Glenn Gaetani, Kathyrn Rose-Pietro, and Peter Landry, for their invaluable assistance in making this work possible. We’d also like to thank Yolande Berta and Georgia Tech’s Center for Nanostructure Characterization for providing access to their SEM facilities, and the Khaled bin Sultan Living Ocean Foundation and The Nature Conservancy for financial and logistical support for field excursions to Palmyra. Funding for this work was provided by the National Science Foundation (Award #s 1502832 and 2002458 to K.M.C) and the National Oceanic and Atmospheric Administration (Award#: NA11OAR4310165 to K.M.C). ERSST V3b data provided by the NOAA PSD, Boulder, Colorado, USA, from their web site (http://www.cdc.noaa.gov/). New records presented in this study are archived on the Paleoclimatology section of the NOAA National Centers for Environmental Information data repository (link pending)