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)