Quantifying errors in coral‐based ENSO estimates: Toward improved forward modeling of δ18O. (16th October 2013)

• Record Type: Journal Article
• Authors: Stevenson, S.; McGregor, H. V.; Phipps, S. J.; Fox‐Kemper, Baylor
• Is Part Of: Paleoceanography. Volume 28:Number 4(2013:Dec.)
• Page Start: 633
• Page End: 649
• Publication Date: 2013-10-16
• Subjects: Paleoceanography -- Periodicals; 551.46
• DOI: 10.1002/palo.20059
• Languages: English
• ISSNs: 0883-8305

Abstract

<abstract abstract-type="main" id="palo20059-abs-0001"> <title> <x xml:space="preserve">Abstract</x> </title> <p id="palo20059-para-0001">[1] The oxygen isotopic ratio (<italic>δ</italic><sup>18</sup>O) in tropical Pacific coral skeletons reflects past El Niño–Southern Oscillation (ENSO) variability, but the <italic>δ</italic><sup>18</sup>O‐ENSO relationship is poorly quantified. Uncertainties arise when constructing <italic>δ</italic><sup>18</sup>O data sets, combining records from different sites, and converting between <italic>δ</italic><sup>18</sup>O and sea surface temperature (SST) and salinity (SSS). Here we use seasonally resolved <italic>δ</italic><sup>18</sup>O from 1958 to 1985 at 15 tropical Pacific sites to estimate these errors and evaluate possible improvements. Observational uncertainties from Kiritimati, New Caledonia, and Rarotonga are 0.12–0.14‰, leading to errors of 8–25% on the typical <italic>δ</italic><sup>18</sup>O variance. Multicoral syntheses using five to seven sites capture the principal components (PCs) well, but site selection dramatically influences ENSO spatial structure: Using sites in the eastern Pacific, western Pacific warm pool, and South Pacific Convergence Zone (SPCZ) captures "eastern Pacific‐type" variability, while "Central Pacific‐type" events are best observed by combining sites in the warm pool and SPCZ. The major obstacle to quantitative ENSO estimation is the <italic>δ</italic><sup>18</sup>O/climate conversion, demonstrated by the large errors on both <italic>δ</italic><sup>18</sup>O variance and the amplitude of the first principal component resulting from the use of commonly employed bivariate formulae to relate SST and SSS to <italic>δ</italic><sup>18</sup>O. Errors likely arise from either the instrumental data used for pseudoproxy calibration or influences from other processes (<italic>δ</italic><sup>18</sup>O advection/atmospheric fractionation, etc.). At some sites, modeling seasonal changes to these influences reduces conversion errors by up to 20%. This indicates that understanding of past ENSO dynamics using coral <italic>δ</italic><sup>18</sup>O could be greatly advanced by improving <italic>δ</italic><sup>18</sup>O forward models.</p> </abstract>