DOI: 10.25921/487b-cm78
title: NOAA/WDS Paleoclimatology - Rabaul - Stable Isotope and Sr/Ca Data

description: We have generated monthly resolved, stable isotope (d18O and d13C)  and Sr/Ca time series from a massive Porites coral from Rabaul  (4ï¿½S, 152ï¿½E): a site located in the warmest sector of the Western  Pacific Warm Pool (WPWP). The coral d18O and Sr/Ca time series are  well correlated to each other and positive excursions in both records  coincide with times of ENSO warm phase events. These time series  contain abundant interannual variability that exhibits the well- recognized pattern of low amplitude ENSO variation between ~1920ï¿½1960  and high amplitude ENSO variation between 1880ï¿½1920 and 1960ï¿½1997.  The ENSO-filtered coral d18O and Sr/Ca time series are well matched  to each other (r = 0.73) and to similarly filtered coral d18O records  from Papua New Guinea (r > 0.56). There is no long-term trend in the  coral d18O record, but there is a long-term trend of increasing coral  Sr/Ca from 1867 to 1997. This trend in coral Sr/Ca suggests a cooling  of ~0.7ï¿½C, which is rather unlikely and implies that factors other than  SST may be influencing the coral Sr/Ca record. The trend in coral Sr/Ca  is not an analytical artifact, nor a product of time varying riverine  input, nor a product of skeletal diagenesis, nor the results of kinetic  effects, but may reflect surface-water variability in Sr/Ca.  Despite the presence of a nonclimatic trend in coral Sr/Ca,  the Rabaul coral records contain abundant interannual- to multidecadal- scale variability, much of which is coherent with other proxy records  from the WPWP and with instrumental records of ENSO variability.
description: A ~1.8 m Porites lobata coral head was recovered in ~8 m of water from offshore of Rabaul, East New Britain, Papua New Guinea (4°11.493'S, 151°58.63'E) in September, 1998. A 5-mm thick slab of the coral core was sampled for geochemical analyses every 0.625 mm along the major axis of coral growth. Petrographic thin sections and SEM images were examined for evidence of secondary minerals; none was observed in the 0-174 cm section of the coral core used in this study. The basal section of the core was not used in this study because it is characterized by extensive evidence of alteration (Quinn and Taylor, 2006). Stable isotopic and elemental ratio determinations were made on splits of the same powder using instrumentation at the University of South Florida (USF; ThermoFinnigan DeltaPlus with Kiel III carbonate device and Perkin Elmer 4300 DV Inductively Coupled Plasma Optical Emissions Spectrometer). Stable isotopic precision, based on daily measurements of laboratory standards (N > 500) over the past 12 months, is ±0.06 per mil (1 sigma) for oxygen, ±0.03 per mil (1 sigma) for carbon. All values are reported in standard delta notation relative to the VPDB isotopic standard using the conventional notation. Analytical precision for Sr/Ca determinations, based on repeated measurements of an internal gravimetric standard (n > 25,000), is ±0.14% (2 sigma; ±0.013mmol/mol) and is ±0.25% (2 sigma; ±0.022 mmol/mol) based on repeated measurements of a homogenized coral powder (n > 600). The pooled standard deviation of >100 Sr/Ca analyses on replicate samples is 0.030 mmol/mol. The accuracy of our standard's Sr/Ca value has been externally verified by TIMS analysis at the University of Minnesota Isotope Laboratory. LAST UPDATE: This file corrected 2019-07-03. Column headers for columns 4 and 5 (d13C and Sr/Ca) switched to correct an earlier error. Data values were not affected.