DOI: 10.25921/8kkt-0207
title: NOAA/WDS Paleoclimatology - Punta Pitt - Stable Isotope and Ion Data  1936-1982

description: A variety of geochemical tracers has been developed in reef corals as a means of reconstructing the natural variability of the tropical surface ocean over wide ranging time frames. The purpose of this paper is to calibrate the performance of five of these tracers in a modern coral colony, over an extended period. A 47-year growth interval (1936–1982) in a colony of Pavona clavus taken from San Cristobal Island, Galapagos Islands, was sectioned into 187 quarterly intervals and analyzed for δ18O, δ13O, Ba/Ca, Cd/Ca, and Mn/Ca. The resulting time series are compared with eastern Pacific sea surface temperatures—one of few instrumental data bases available for calibration over this time period. Linear least squares regressions of four of the tracers (δ18O, δ13O, Ba/Ca, Cd/Ca) against Peruvian SST show highly significant correlations (p<0.0001). Over the annual, biennial, and ENSO (3.8 years) frequency bands, cross-spectral comparisons show even stronger coherency, with SST frequently accounting for 70–80% of the variance in these tracers. These results as well as the phase relationships determined from the spectral analyses suggest that the coupling between SST and δ18O and the nutrientlike tracers Ba and Cd is controlled principally by seasonal upwelling cycles and interannual interruptions of these cycles brought about by El Niño and anti-El Niño phenomena. An inverse relationship between SST and δ13C has its primary origins in the co-occurrence of the warm SST phase with high light levels during the first half of the calendar year. The association with sunlight derives from the photosynthetic response of algal symbionts which results in fractionation of light and heavy carbon isotopes between soft tissues and CaCO3 skeleton. The fifth tracer, the transition metal Mn, exhibits poorer correlations against both SST and the other tracers. Slight shifts in phasing of the historical Mn/Ca annual cycle suggest that the general water column distribution of this tracer, which is the reverse of a nutrient, may not be stable. The erratic behavior of Mn illustrates how complex hydrography near Galapagos may influence tracers with diverse source signatures.
description: Site: Punta Pitt, Isla San Cristobal, Galapagos Islands, Ecuador (0 40'S, 89 10'W). Water depth 14m. Coral species Pavona clavus. Time span: 1936-1982.5 at quarterly resolution (missing data from 1950). File contains data presented by Shen et al. (1992a). Table includes d18O, d13C, Cd/Ca, Mn/Ca, and Ba/Ca data from a 2m coral head and, for comparison, SST records from Academy Bay (Galapagos; 0 40'S, 90 20'W) and Puerto Chicama (Peru; 8 S, 80 W). All coral measurements derive from the same samples, which were treated as described in Shen et al. (1992a). Stable isotopes were measured at Lamont-Doherty Earth Observatory by  J. Cole and R. Fairbanks on a Finnigan MAT-251 mass spectrometer with automated Carousel-48 carbonate device; values are in standard per mil notation relative to PDB. Cd/Ca and Mn/Ca were measured at the University of Washington by G. Shen and L. Linn on a Hitachi Z-9000 multichannel atomic absorption spectrophotometer. Ba/Ca was measured at the University of California/Santa Barbara by D. Lea on a VG Elemental PQ2+ inductively coupled plasma mass spectrometer. Measurement precisions are as follows: 0.08‰ d18O; 0.04‰ d13C; 9.8% for Cd/Ca; 6.6% for Mn/Ca; 1% for Ba/Ca. Ages for samples were assigned on the basis of well-defined density banding, assuming that the base of the dense band corresponds to February and that extension rates between these points are linear. Coral measurements were made at quarterly resolution. SST records were averaged from monthly resolution to quarterly based on the following 3-month groupings: Feb-Mar-April, May-June-July, Aug-Sep-Oct, and Nov-Dec-Jan.