DOI: 10.25921/nkb2-v761
title: NOAA/WDS Paleoclimatology - Galapagos Fossil and Modern Coral Geochemical and Density Data

description: Coral geochemical climate reconstructions can extend our knowledge of global climate variability and trends over time scales longer than those of instrumental data. However, such reconstructions can be biased by coral growth and skeletal architecture, such as growth troughs, off-axis corallite orientation, and changing growth direction. This study quantifies the impact of skeletal architecture and growth on geochemistry using measurements of coral skeletal density, extension rate, and calcification rate, and uses these metrics to improve paleoclimate reconstructions. We present paired geochemistry-density records at Wolf Island, Galápagos, from three Porites lobata corals: two new paired density and geochemistry records from one fossil coral, and new density data from two previously published modern geochemistry records. We categorize each sampling transect used in this record by the quality of its orientation with respect to skeletal architecture. We observe relationships between geochemistry and density that are not detected using extension or calcification rate alone. These density-geochemistry relationships likely reflect both the response of coral growth to environmental conditions and the nonclimatic impact of skeletal architecture on geochemistry in suboptimal sampling transects. Correlations of density with Sr/Ca, Ba/Ca, and Mg/Ca are consistent with the Rayleigh fractionation model of trace element incorporation into coral skeletons. Removing transects with suboptimal skeletal architecture increases mean reconstructed SST closer to instrumental mean SST, and lowers errors of reconstruction by up to 20%. These results demonstrate the usefulness of coral density data for assessing skeletal architecture and growth when generating coral paleoclimate records.
description: Coral trace metal (Sr/Ca, Mg/Ca, and Ba/Ca) and skeletal density data from living and fossil samples collected near Wolf Island, Galapagos. Trace metal (Sr/Ca, Mg/Ca, and partial Ba/Ca) and coral skeletal density data are given after interpolating to monthly resolution, and, as in the publication, data are NOT averaged between overlapping transects to produce a single continuous time series. Analytical precisions for trace metals (+/- 1 standard deviation): Sr/Ca=0.031 mmol/mol; Mg/Ca=0.189 mmol/mol; Ba/Ca=0.188 umol/mol. Trace element data were corrected to an internal coral standard, and the inter-laboratory standard JCp-1 was measured for comparison. WLF04 and WLF05 are cored from the same subfossil coral colony and U/Th dated; WLF10 and WLF03 were collected from different live coral colonies. Both monthly data (trace elements, density) and annual data (trace elements, density, extension, and calcification) are given, where “annual” is defined as the time between successive March tie points, determined from Sr/Ca minima (inferred SST maxima). WLF03 and WLF10 Sr/Ca were previously published in Jimenez et al. (2018), and the data here differ slightly from the prior publication: these data are presented in monthly resolution (as opposed to bimonthly resolution), are corrected to updated known values of the internal coral standard, and are not averaged between overlapping transects. Additionally, colony growth data (density, extension, and calcification) are new in this study.