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. 2016 May 31:6:26888.
doi: 10.1038/srep26888.

Understanding cold bias: Variable response of skeletal Sr/Ca to seawater pCO2 in acclimated massive Porites corals

Catherine Cole  1 , Adrian Finch  1 , Christopher Hintz  2 , Kenneth Hintz  3 , Nicola Allison  1
Affiliations

Understanding cold bias: Variable response of skeletal Sr/Ca to seawater pCO2 in acclimated massive Porites corals

Catherine Cole et al. Sci Rep. .

Abstract

Coral skeletal Sr/Ca is a palaeothermometer commonly used to produce high resolution seasonal sea surface temperature (SST) records and to investigate the amplitude and frequency of ENSO and interdecadal climate events. The proxy relationship is typically calibrated by matching seasonal SST and skeletal Sr/Ca maxima and minima in modern corals. Applying these calibrations to fossil corals assumes that the temperature sensitivity of skeletal Sr/Ca is conserved, despite substantial changes in seawater carbonate chemistry between the modern and glacial ocean. We present Sr/Ca analyses of 3 genotypes of massive Porites spp. corals (the genus most commonly used for palaeoclimate reconstruction), cultured under seawater pCO2 reflecting modern, future (year 2100) and last glacial maximum (LGM) conditions. Skeletal Sr/Ca is indistinguishable between duplicate colonies of the same genotype cultured under the same conditions, but varies significantly in response to seawater pCO2 in two genotypes of Porites lutea, whilst Porites murrayensis is unaffected. Within P. lutea, the response is not systematic: skeletal Sr/Ca increases significantly (by 2-4%) at high seawater pCO2 relative to modern in both genotypes, and also increases significantly (by 4%) at low seawater pCO2 in one genotype. This magnitude of variation equates to errors in reconstructed SST of up to -5 °C.

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Figures

Figure 1
Figure 1. Multiple genotypes of massive Porites spp. stained with alizarin.
Representative colonies of (a) Porites lutea genotype 1; (b) Porites lutea genotype 2; (c) Porites murrayensis, cultured at ambient pCO2 within our aquarium system. (d) Alizarin stain lines mark skeletal extension during the 5-week experimental period. Scale bars are 1mm.
Figure 2
Figure 2. Influence of seawater pCO2 on coral aragonite:seawater Sr/Ca partition coefficients (KDSr/Ca) for 3 genotypes of Porites spp. following acclimation to 198, 416 and 750 μatm pCO2 at 25 °C.
Bars represent the mean KDSr/Ca of multiple analyses (n = 12–41; see Table S1) across 2 or more skeletal units within individual colonies. Within each species/genotype, different letters indicate significant differences between treatments (p < 0.05; ANOVA and Tukey post-hoc). Error bars represent the combined 95% confidence limits of seawater and skeletal Sr/Ca measurements.
Figure 3
Figure 3. Genotypic variations in mean coral aragonite: seawater KDSr/Ca in individual colonies of Porites spp. following >5 months of acclimation to 198, 416 and 750 μatm3 pCO2 at 25 °C.
Within each pCO2 treatment, different letters indicate significant differences between genotypes (p < 0.05; ANOVA and Tukey post-hoc). Error bars represent the combined 95% confidence limits of seawater and skeletal Sr/Ca measurements.
See this image and copyright information in PMC

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