A biological origin for climate signals in corals—Trace element “vital effects” are ubiquitous in Scleractinian coral skeletons

Abstract

Laser ablation ICP/MS was used to analyze Mg, Sr and U at fine (hundreds of microns) and seasonal spatial scales in the reef coral Porites and the non‐photosynthetic “deep‐sea” corals Lophelia, Oculina, and Desmophyllum. Tropical corals display strong seasonal correlations between Mg, Sr and U, even when normal cycles are perturbed by unknown factors. An inverse relationship between Mg and U is a universal feature of all the corals, but is much larger in deep corals despite stable environmental conditions. This correlation originates from two aragonitic skeletal types: Mg‐rich opaque centers of calcification, and U‐rich large translucent crystals. The Mg‐rich material probably precipitates rapidly and corresponds to materials strongly deficient in 18O and 13C compared to isotopic equilibrium. Combined, these observations imply that varying proportions of the two skeletal types may account for most of the “temperature” or “climate” signal in tropical corals, as well as anomalous “vital effects”.

The influence of seawater pH on U / Ca ratios in the scleractinian cold-water coral <i>Lophelia pertusa</i>

“…Using a seawater U / Ca ratio of 1.305 µmol mol −1 (Chen et al, 1986), the partition coefficient D U = (U / Ca) skeleton / (U / Ca seawater ) varies between 0.9 and 1.6 and is in line with previous studies of U / Ca in CWCs (Anagnostou et al, 2011;Montagna et al, 2005;Sinclair et al, 2006). However, the observed CWC carbonate U / Ca ratios exhibit a two-fold greater variability compared to tropical corals (Shen and Dunbar, 1995;Inoue et al, Error bars correspond to pH of ±0.15.…”

“…7). Previous studies that analysed Mg / Ca ratios in L. pertusa show comparable absolute values in the theca wall as well as in the COC (compare Cohen et al, 2006;Sinclair et al, 2006). These studies could clearly identify the COC by scanning electron microscope pictures.…”

“…Besides the uranium speciation, the effect of growth rates on coral U / Ca ratios has been investigated and discussed more thoroughly (e.g. Anagnostou et al, 2011;Inoue et al, 2011;Min et al, 1995;Sinclair et al, 2006). The latter study suggested that two different aragonitic endmembers may cause the different element composition.…”

“…Furthermore, a lower U content in the COC compared to the majority of the skeleton has been observed in other CWCs (Robinson et al, 2006;Sinclair et al, 2006). Some models attempting to explain the trace metal and isotope incorporation into corals suggest that Rayleigh fractionation from a closed system plays a significant role (e.g.…”

Coral skeleton P/Ca proxy for seawater phosphate: Multi-colony calibration with a contemporaneous seawater phosphate record

“…This confirms that most (70-90%) of the variation in the P/Ca of an individual coral can be explained by changes in PO 4 SW . The remaining 10-30% variability in P/Ca could result from other factors including biologically-regulated "vital effects", extension rate (de Villiers et al, 1995;Sinclair et al, 2006), or the influence of additional seawater conditions on P incorporation (Section 3.4). The mean slope and y-intercept, with average deviation for both (n = 3 colonies per species), were calculated from the individual colony regressions to create the following multi-colony calibrations.…”