DOI: 10.25921/x5sp-6y18
title: NOAA/WDS Paleoclimatology - Palmyra Island,Fanning Island,Kiritimati Island - Line Islands Coral SST and d18Osw Reconstructions

description: Global climate models and analyses of instrumental datasets provide a wide range of scenarios for future tropical Pacific climate change, limiting the accuracy of regional climate projections. Coral records provide continuous reconstructions of tropical Pacific climate trends that are difficult to quantify using the short, sparse instrumental datasets available from the tropical Pacific. Here, we present coral-based reconstructions of late 20th century sea-surface temperature and salinity trends from several islands in the central tropical Pacific. The coral data reveal warming trends that increase towards the equator, implying a decrease in equatorial upwelling in the last decades. Seawater freshening trends on the southern edge of the Inter-Tropical Convergence Zone suggest a strengthening and/or an equatorward shift of the convergence zone. Together, the new coral records support a late 20th century trend towards “El Niño-like” conditions in the tropical Pacific, in line with the majority of coupled global climate model projections.
description: This dataset contains coral-derived sea-surface temperature (SST, via Sr/Ca) and salinity (SSS, via d18Osw) reconstructions from Palmyra, Fanning, and Christmas Islands, Line Islands, central tropical Pacific, for the period 1972-1998 (to 2005 for Fanning). Cobb et al. [2001] presented the century-long oxygen isotopic (d18O) record from Palmyra, and we present new d18O records from Fanning and Christmas, in addition to new Sr/Ca records from Palmyra, Fanning, and Christmas. We measured coral d18O values on a GV Isoprime-Multiprep mass spectrometer with an analytical precision of ± 0.06‰ (1ó), and Sr/Ca ratios with a Jobin Yvon Ultima 2C Inductively Coupled Plasma-Optical Emission Spectrometer (ICP-OES) with an analytical precision of ± 0.08-0.24% or ± 0.11-0.27ºC (1ó) 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%), (SST)fann = 166.81 – 15.47 x (Sr/Ca)fann (Nov 1981-June 2005; R=-0.79; CI > 99%), (SST)chrs = 141.57 – 12.66 x (Sr/Ca)chrs (Nov 1981-Mar 1998; R=-0.80; CI > 99%). The Fanning d18O and Sr/Ca records were constructed by splicing records from two separate coral cores (spliced at 1984) in order to avoid diagenesis evident in one of the cores. 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 for Palmyra: d18O, Sr/Ca-derived SST and d18Osw records from 1972 to 1998 were used in the trend calculations reported in the paper, while Sr/Ca record from 1981-1998 was used for the Sr/Ca-SST calibration. Note for Fanning: d18O, Sr/Ca-derived SST and d18Osw records from 1972 to 1998 were used in the trend calculations reported in the paper, while Sr/Ca record from 1981-2005 was used for the Sr/Ca-SST calibration. Spliced Fanning timeseries are constructed by splicing Fanning core 1 to Fanning core 2 at time 1984. These are the records used in the calibration and trend analyses, and in the construction of the Fanning d18Osw record. Note for Christmas Island: d18O, Sr/Ca-derived SST and d18Osw records from 1972 to 1998 were used in the trend calculations reported in the paper, while Sr/Ca record from 1981-1998 was used for the Sr/Ca-SST calibration.