DOI: 10.25921/f93r-0r11
title: NOAA/WDS Paleoclimatology - Amédée Island, New Caledonia, 350 Year Coral Sr/Ca SST Reconstruction

description: A prime focus of research is differentiating the contributions of natural climate variability from those that are anthropogenically forced, especially as it relates to climate prediction. The short length of instrumental records, particularly from the South Pacific, hampers this research, specifically for investigations of decadal to centennial scale variability. Here we present a sea surface temperature (SST) reconstruction derived from highly reproducible records of strontium-to-calcium ratios (Sr/Ca) in corals from New Caledonia to investigate natural SST variability in the southwest tropical Pacific from AD 1649-1999. Our results reveal periods of warmer and colder temperatures of the order of decades during the Little Ice Age that do not correspond to long-term variations in solar irradiance or the 11-year sunspot cycle. We suggest that solar variability does not explain decadal to centennial scale SST variability in reconstructions from the southwest tropical Pacific. Our SST reconstruction covaries with the Southern Hemisphere Pacific decadal oscillation and the South Pacific decadal oscillation, from which SST anomalies in the southwest Pacific are linked to precipitation anomalies in the western tropical Pacific. We find that decadal scale SST variability has changed in strength and periodicity after 1893, suggesting a shift in natural variability for this location.
description: Coral Sr/Ca data and Sea Surface Temperature (SST) reconstruction for the past 350 years for New Caledonia, western tropical Pacific. Cores sampled include: two long cores (92-PAA1 and 92-PAA2) and one shorter core (99-PAA) from a single massive Porites lutea colony (PAA), and two cores (92-PAC and 92-PAD) from nearby colonies of the same species, all recovered from colonies offshore of Amédée Island, New Caledonia (Stephans et al., 2004; DeLong et al, 2007; DeLong et al, 2012a; DeLong et al, 2012b). Previous studies with this suite of coral colonies discuss the location and sampling methods (Quinn et al, 1996; Quinn et al, 1998; Stephans et al, 2004; DeLong et al, 2007).
 
Elemental ratio (Sr/Ca) determinations follow the method previously described by DeLong et al. (2007). The elemental data were analyzed on a Perkin Elmer Optima 4300DV ICP-OES following the drift-correction methods of Schrag (1999) at the University of South Florida (USF) and University of Texas. For cores 92-PAA1 and 92PAA2, the one-sigma analytical precision of a laboratory internal gravimetric standard is ±0.010 mmol per mol (n = 2,445) and of a homogenized powder from a Porites lutea coral is ±0.018 mmol per mol (n = 3,343), which is an additional estimate of precision. For cores 99-PAA, 92-PAC and 92-PAD, the analytical precision is reported by Stephans et al. 2004 and summarized here. Analytical precision (1 sigma) for the Sr/Ca determinations is 0.2% (0.018 mmol per mol), based on a laboratory standard solution of dissolved Porites lutea. The isotope data were analyzed at the University of South Florida College of Marine Science, on a Finnigan Delta Plus XL mass spectrometer and attached Kiel Carbonate Device with an analytical precision of 0.04 per mil for carbon and 0.08 per mil for oxygen (1 sigma) determined by repeated measurements of NBS 19 relative to VPDB. Stable isotopic and Sr/Ca determinations on samples from Cores 99-PAA, 92-PAC and 92-PAD were made at USF. Stable isotopic determinations on samples from core 92-PAA made at the University of Michigan.
 
Depth series were converted to time series using AnalySeries software (Paillard et al., 1996) to match Sr/Ca minima to SST maxima and vice versa. We established our master chronology with sclerochronology methods (DeLong et al., 2007; DeLong et al., 2012b) confirmed with 11 high-precision Th-230 dates (DeLong et al., 2012b; Shen et al., 2008). Coral Sr/Ca variations were compiled into a single time series by averaging contemporaneous monthly coral Sr/Ca variations from sampling paths within each colony, and then by averaging the coral Sr/Ca variations from the colonies together. The monthly-resolved coral Sr/Ca variations were converted to SST with the transfer equation previously determined for these corals, which were calibrated to 32-years of in situ SST (IRD-SST) from Institut de Recherche pour le Développement - Etudes Climatiques de l’Océan Pacifique tropical (IRD-ECOP) from Amédée Island, New Caledonia (DeLong et al., 2007). This calibration was verified with the 1-degree grid centre on our study site (22.5ºS, 166.5ºE; HadISST-AI) extracted from the HadISST1.1 database (Rayner et al., 2003), which was adjusted to match mean and variance of IRD-SST (DeLong et al., 2007). 
 
The error of the reconstruction was evaluated for varying scales from a single core to five cores by determining the standard error of regression (sR) for the calibration interval (1967-1992). This allows the sR shown by error bars in Fig. 2 of DeLong et al., 2012 Nature Climate Change to vary with time based on the number of cores. Time series smoothed with low pass finite impulse response (LPFIR) filter (Bloomfield, 2000). Anomalies determined with respect to average monthly values for the given interval. Time were detrended with a second order polynomial fit, see DeLong et al. 2012 Nature Climate change for equations.
 
The columns contain reference to figure numbers from cited references. The data from problematic paths presented in Figure 7 of DeLong et al., 2012 in P3 is given for instructions purposes ONLY and SHOULD NOT BE USED FOR CLIMATE RECONSTRUCTIONS.  

Note: A portion of this data replaces the data previously reported and archived by Stephans et al., 2004.

Amédée Island, New Caledonia:  22°28.5'S, 166°28'E, water depth 3 m.