Monthly Strontium/Calcium oscillations in symbiotic coral aragonite: Biological effects limiting the precision of the paleotemperature proxy

Abstract

In thermodynamic equilibrium with sea water the Sr/Ca ratio of aragonite varies predictably with temperature and the Sr/Ca ratio in coral have thus become a frequently used proxy for past Sea Surface Temperature (SST). However, biological effects can offset the Sr/Ca ratio from its equilibrium value. We report high spatial resolution ion microprobe analyses of well defined skeletal elements in the reef‐building coral Porites lutea that reveal distinct monthly oscillations in the Sr/Ca ratio, with an amplitude in excess of ten percent. The extreme Sr/Ca variations, which we propose result from metabolic changes synchronous with the lunar cycle, introduce variability in Sr/Ca measurements based on conventional sampling techniques well beyond the analytical precision. These variations can limit the accuracy of Sr/Ca paleothermometry by conventional sampling techniques to about 2°C. Our results may help explain the notorious difficulties involved in obtaining an accurate and consistent calibration of the Sr/Ca vs. SST relationship.

Reconstructing twentieth‐century sea surface temperature variability in the southwest Pacific: A replication study using multiple coral Sr/Ca records from New Caledonia

“…Sinclair [2005] microsampled Porites corals from the Great Barrier Reef, Australia and reported large-magnitude, submonthly coral Sr/Ca variability, which would equate to $20°C. Unlike Meibom et al [2003] and Cohen and Sohn [2004], Sinclair [2005] did not observe concentrations of variance at common periodicities and noted different variations between corals. Previous coral-based climate reconstructions contrast with micron-scale investigations, which use micron-scale sampling to recover $1 mm 2 area from within a single corallite, whereas typical coral-based climate reconstructions sample an $1 mm 2 area which may contain multiple corallites depending on the species.…”

“…Meibom et al [2003] observed approximately monthly oscillations in coral Sr/Ca sampled at 30 mm (approximately daily), which they attributed to metabolic variability related to the lunar cycle. Cohen and Sohn [2004] attributed coral Sr/Ca variations sampled in discrete 20 mm spots (approximately daily) to tidal forcing.…”

“…[24] Recent investigations of micron-scale variations in coral skeletal Sr/Ca concluded that micron-scale frequency variations in coral Sr/Ca are not related to SST variations [Meibom et al, 2003;Allison and Finch, 2004;Cohen and Sohn, 2004;Sinclair, 2005]. Meibom et al [2003] observed approximately monthly oscillations in coral Sr/Ca sampled at 30 mm (approximately daily), which they attributed to metabolic variability related to the lunar cycle.…”

Reconstructing skeletal fiber arrangement and growth mode in the coral <i>Porites lutea</i> (Cnidaria, Scleractinia): a confocal Raman microscopy study

“…Sr / Ca) did not only depend on the target parameter (e.g. T ) but was potentially influenced by other parameters like (1) metabolic changes involving spawning and larval release at a lunar periodicity (Meibom et al, 2003), (2) weekly tidal forcing overlying temperature forcing (Cohen and Sohn, 2004), and (3) a strong bi-weekly periodicity that was hypothesized to result from increased calcification required for the formation of synapticulae (Cohen and Sohn, 2004). The latter corresponds to the biweekly growth bands (ORGL 2) described in this study.…”

“…Meibom et al, 2007). High-resolution proxy studies detected a cyclicity of measured proxy values in the range of weekly to monthly periods (Meibom et al, 2003;Rollion-Bard et al, 2003;Cohen and Sohn, 2004;Allison et al, 2010Allison et al, , 2011. In these studies the proxy relation (e.g.…”