Coral-based estimates of tropical Pacific climate during the Little Ice Age: Intercolony variability and the need for replication

Hussein R Sayani1, Kim M Cobb2, Agraj Khare2,3, Colin Stone2, Pamela R Grothe2, Tianran Chen2, Yanbin Lu4, Hai Cheng5 and R. Lawrence Edwards6, (1)Georgia Institute of Technology, Earth and Atmospheric Sciences, Atlanta, GA, United States, (2)Georgia Institute of Technology Main Campus, Earth and Atmospheric Sciences, Atlanta, GA, United States, (3)University of Maryland Center for Environmental Science, Chesapeake Biological Laboratory, Solomons, MD, United States, (4)University of Minnesota, Department of Earth Sciences, Minneapolis, MN, United States, (5)Xi'an Jiaotong University, Institute of Global Environmental Change, Xi'an, China, (6)University of Minnesota, Minneapolis, MN, United States
Abstract:
Massive surface corals offer continuous, high-resolution records of tropical climate variability, but reconstructing climate beyond the last century requires combining records from many different coral colonies [e.g. Cobb et al., 2003]. When combining coral records to build a reconstruction, however, one must grapple with the fact that corals growing on the same reef can yield Sr/Ca and δ18O records with significantly different mean values. These intercolony offsets equate to uncertainties of 1-3˚C when converted to SST [e.g. Felis et al., 2003; DeLong et al., 2011], significantly larger than the magnitude of decadal- to centennial-scale tropical climate variability during the last millennium [Emile-Geay et al., 2013]. Using a large suite of modern coral cores from Palmyra Atoll (6°N, 162°W), we quantify intercolony variability in Sr/Ca and δ18O records with respect to Sr/Ca-SST slopes and mean offsets. We document intercolony Sr/Ca offsets of ±0.09mmol/mol (1σ) or ~1˚C, and δ18O offsets of ±0.04‰ or ~0.2˚C. Sr/Ca-SST calibrations from six cores differ by ±5%, yielding temperatures ranging 26˚C to 29˚C when applied to a given coral Sr/Ca value. While individual corals are associated with large uncertainties, a composite of six modern cores offers a much reduced error bar of ±0.6˚C (1s). Applying these lessons to paired Sr/Ca and δ18O records from 3 Palmyra fossil corals from the 17th century, we find that central tropical Pacific (CTP) SST during the Little Ice Age (LIA) was 1.7±0.9˚C cooler than the 20th century. Seawater δ18O estimates derived from these fossil corals suggest drier conditions at Palmyra, consistent with lake sediment records from the Line Islands [Sachs et al., 2009].

References:
Cobb, K. M., et al. (2003) Nature. 10.1038/nature01779
DeLong, K. L., et al. (2011) Palaeogeo Palaeoclim Palaeoeco. 10.1016/J.Palaeo.2011.05.005
Emile-Geay, J., et al. (2013) Journal of Climate. 10.1175/JCLI-D-11-00511.1
Felis, T., et al. (2003) Coral Reefs. 10.1007/s00338-003-0324-3
Sachs, J. P., et al. (2009) Nature Geoscience. 10.1038/ngeo554

Back to: High-Resolution Geochemical Proxies of Global Change: Progress, Problems, and Utility II Posters