DOI: 10.25921/kxxr-wb79
title: NOAA/WDS Paleoclimatology - Palmyra Island Coral 110 Year Sr/Ca SST and d18Osw

description: Accurate projections of future temperature and precipitation patterns in many regions of the world depend on quantifying anthropogenic signatures in tropical Pacific climate against its rich background of natural variability. However, the detection of anthropogenic signatures in the region is hampered by the lack of continuous, century-long instrumental climate records. This study presents coral-based sea surface temperature (SST) and salinity proxy records from Palmyra Island in the central tropical Pacific over the twentieth century, based on coral strontium/calcium and the oxygen isotopic composition of seawater (δ18OSW), respectively. On interannual time scales, the Sr/Ca-based SST record captures both eastern and central Pacific warming “flavors” of El Niño–Southern Oscillation (ENSO) variability (R = 0.65 and 0.67, respectively). On decadal time scales, the SST proxy record is highly correlated to the North Pacific gyre oscillation (NPGO) (R = −0.85), reflecting strong dynamical links between the central Pacific warming mode and extratropical decadal climate variability. Decadal-scale salinity variations implied by the coral-based δ18OSW record are significantly correlated with the Pacific decadal oscillation (PDO) (R = 0.54). The salinity proxy record is dominated by an unprecedented trend toward lighter δ18OSW values since the mid–twentieth century, implying that a significant freshening has taken place in the region, in line with climate model projections showing enhanced hydrological patterns under greenhouse forcing. Taken together, the new coral records suggest that low-frequency SST and salinity variations in the central tropical Pacific are controlled by different sets of dynamics and that recent hydrological trends in this region may be related to anthropogenic climate change.
description: This dataset contains coral-derived sea-surface temperature (SST, via Sr/Ca) and salinity (SSS, via the oxygen isotopic composition of seawater or d18Osw) reconstructions from Palmyra Island of the Line Islands chain in the central tropical Pacific, for the period 1886-1998. Cobb et al. [2001] presented the century-long coral oxygen isotopic (d18O) record from Palmyra, and here we present the century-long Sr/Ca and d18Osw records from Palmyra. The late 20th century portion of the Sr/Ca and d18Osw records was presented in Nurhati et al.[2009]. We measured coral d18O values on a GV Isoprime-Multiprep mass spectrometer with an analytical precision of ± 0.05‰ (1sigma), and Sr/Ca ratios with a Jobin Yvon Ultima 2C Inductively Coupled Plasma-Optical Emission Spectrometer (ICP-OES) with an analytical precision of ± 0.07% or ± 0.006 mmol/mol(1s) using the nearest-neighbor correction method from Schrag [1999]. We used the monthly 1ºx1º IGOSS SST dataset [Reynolds et al., 2002] to calibrate Sr/Ca ratios via reduced major axis regression, where (SST)palm = 130.43 – 11.39 x (Sr/Ca)palm (Nov 1981-Mar 1998; R=-0.71; CI > 99%). We derive the oxygen isotopic composition of seawater (d18Osw) by subtracting the Sr/Ca-derived SST contribution from coral d18O following the method outlined in Ren et al. [2003]. Fairbanks et al. [1997] find an empirical linear relationship between d18Osw and SSS in the central tropical Pacific, so we use the d18Osw records to reconstruct SSS variability associated with changes in the hydrological balance.  Note: Coral d18O data has been previously published by Cobb et el. (2001). Sr/Ca data from 1981-1998 was used for the Sr/Ca-SST calibration. Coral d18O, Sr/Ca-derived SST and d18Osw data from 1886 to 1998 were used in the trend calculations reported in the paper. Core location: Palmyra: 5°53'N, 162°5'W, 9m depth