DOI: 10.25921/y8fz-8j47
title: NOAA/WDS Paleoclimatology - New Caledonia Coral Proxy Data Sampling Resolution Comparison

description: Coral-based climate reconstructions typically have not used multiple cores from a region to capture and replicate a climate signal largely because of concerns of coral conservation, analytical expense, and time constraints. Coral Sr/Ca reproducibility through the twentieth century was investigated using three intracolony and three intercolony coral records from the reefs offshore of Amédée Island, New Caledonia. Different sampling resolutions were examined in coral Sr/Ca (fortnightly and monthly) and d18O (fortnightly, monthly, and seasonally) as well as similar scale subsampling of the daily in situ sea surface temperature (SST) record. The mean coral Sr/Ca, d18O, and SST values do not change as a function of sampling resolution. The coral Sr/Ca signal is highly reproducible; the average absolute offset between coeval monthly Sr/Ca determinations between any two coral time series is 0.035 ± 0.026 mmol/mol (1s) (~0.65°C), which is less than twice the analytical precision of the coral Sr/Ca measurements. The stack average of the monthly coral Sr/Ca variations and monthly anomalies are significantly correlated with monthly in situ SST (1967-1992; r = -0.96 and -0.64, respectively; p < 0.05; and n = 302) and 1° grid monthly SST data product (1900-1999; r = -0.95 and -0.56, respectively; p < 0.05; and n = 1198). The coral Sr/Ca-SST reconstruction exhibits interannual and decadal- timescale fluctuations that exceed those observed in the gridded SST record, which may reflect true differences between SST at a shallow reef site and those averaged over a 1° grid box or inadequacies in the methodology used to create the gridded SST product when few observations are available. A warming trend of ~0.6°C is observed in the twentieth century coral Sr/Ca-SST record.
description: Sampling resolution comparison for corals collected at Amédée Island, New Caledonia.  Seasonal, Monthly, and Fortnightly sampling of coral Sr/Ca, Mg/Ca, d18O, and d13C for 1942-1951 AD. The data from the sampling resolution comparison (~seasonal,~monthly, and ~fortnightly) between parallel paths presented in Figure 3 of DeLong et al. 2007. Note: the reminder of the data presented in the study of DeLong et al., 2007 is available in another contribution and cited as DeLong et al., 2012. The coral section, 92-PAA1-B, was originally sampled at 0.28 cm per sample (seasonally) by Quinn et al. 1998. The study of DeLong et al. 2007 sampled the coral slab on either side of the Quinn et al. 1998 path (<0.5 cm) with increasing resolution: 0.0692 cm per sample (monthly) and 0.030 cm per sample (fortnightly) down the core. Refer to figure 2 in DeLong et al. (2007) for sampling path location on the core, which is 1942 to 1951 AD. Coral samples were analyzed for d18O, d13C, Sr/Ca, and Mg/Ca with an analytical precision (1S) of ±0.06‰, ±0.04‰, ±0.017 mmol mol-1, and ±0.024 mmol mol-1, respectively. Note: these Mg/Ca data were not shown or discussed in DeLong et al. 2007; however, these data are provided here for completeness. For Figure 3 in DeLong et al. (2007), the fortnightly Sr/Ca depth was adjusted to align with monthly Sr/ Ca variations, and depth adjustments were applied to other geochemical records; these adjustments are shown in columns labeled "Aligned depth (cm)." The same method of adjustments was applied to the seasonal records using monthly d18O depth. Comparisons are based on depths common to all resolutions (gray rectangle). Mean coral Sr/Ca, d18O, and d13C values do not change significantly as a function of sampling resolution; however, the averages of the summer and winter amplitudes determined for each sampling resolution reveal a decrease in seasonal cycle with decreasing sampling resolution. Amédée Island, New Caledonia:  22°28.5'S, 166°28'E, water depth 3 m.