NOAA/WDS Paleoclimatology - Palmyra Atoll Porites spp. d18O and Sr/Ca Data from 1982-2010 CE

Quantitative estimates of natural climate variability are required to detect anthropogenic climate trends in the tropical Pacific; however, instrumental records from this region are too short and scarce. Coral oxygen isotopic (d18O) and strontium to calcium (Sr/Ca) records are often used to extend instrumental observations; however, differences in the mean Sr/Ca and d18O values of Porites spp. colonies from the same reef can introduce large uncertainties in coral-based climate reconstructions. To quantify intercolony variability at Palmyra Atoll, we generate monthly resolved Sr/Ca and d18O time series from five Porites spp. colonies that grew between 1980 and 2010. Monthly to interannual variability in Sr/Ca and d18O is well-reproduced among different colonies; however, we document intercolony offsets in mean Sr/Ca of ±0.09 mmol/mol (1s) or ~1 °C, and in mean d18O of ±0.12‰ (1s) or ~0.1 °C. The sensitivity of each proxy to climate also varies across colonies, with Sr/Ca-SST slopes ranging from -0.06 to -0.1 mmol mol-1 °C-1 and d18O-SST slopes ranging from -0.25 to -0.35‰ °C-1. Intercolony variability in both coral Sr/Ca and d18O reduces the reproducibility of coral-based d18Osw reconstructions across overlapping colonies. Accounting for both intercolony variability and slope error suggests that SST reconstructions using Sr/Ca from a single Palmyra coral have an uncertainty of ±1.3 °C (1s); however, replicating Sr/Ca records across multiple colonies can greatly reduce this uncertainty. A composite Sr/Ca record built using five modern cores, for example, offers a reduced error of ±0.6 °C (1s) in mean SST reconstructions, ~2.5 times smaller than errors associated with reconstructions from single corals.