Effect of salinity on the skeletal chemistry of cultured scleractinian zooxanthellate corals: Cd/Ca ratio as a potential proxy for salinity reconstruction
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The effect of salinity on the elemental and isotopic skeletal composition of modern zooxanthellate scleractinian corals (Acropora sp., Montipora verrucosa and Stylophora pistillata) was investigated in order to evaluate potential salinity proxies. Corals were cultured in the laboratory at three salinities (36, 38 and 40). The other environmental parameters were kept constant. For all species analyzed, Sr/Ca, Mg/Ca, U/Ca and Li/Ca ratios were not influenced by salinity changes. The Ba/Ca ratio also lacks a systematic relationship with salinity and exhibits high inter-generic variations, up to one order of magnitude. On the contrary, the Cd/Ca ratio decreases as a function of increasing salinity, and δ18O and δ13C also presented a significant response, but with opposite trends to salinity variations. Since Cd/Ca is usually considered as an upwelling proxy, its salinity dependence could compromise the upwelling signal, unless some corrections can be carried out. Regardless, if the dependence found in the present dataset proved to be widespread and systematic, the Cd/Ca ratio could represent a promising salinometer awaiting further investigation. This study also confirmed the reliability of the well-established temperature proxies Sr/Ca, Mg/Ca and U/Ca, as these ratios were insensitive to salinity variations. Moreover, our results showed that δ18O or δ13C can be considered as reliable temperature recorders as far as the salinity effect is removed from the parameter reconstructed (e.g., temperature). Investigating the influence of salinity on the skeletal chemistry of scleractinian corals grown under controlled environmental conditions confirmed previous results, validated isotopic corrections, and identified a promising proxy of salinity.
KeywordsSea-surface salinity (SSS) Sea-surface temperature (SST) Salinity proxy Elemental ratios Carbon isotopes Oxygen isotopes Scleractinians Laboratory culture
The support of the Swiss National Science Foundation (SNF) through Grants 20MA21-115944 and 200020-140618 in the frame of the European Science Foundation (ESF) EUROCORES Program EuroMARC is acknowledged. This work is a contribution to the European Project on Ocean Acidification (EPOCA), which received funding from the European Community’s Seventh Framework Program (FP7/2007-2013) under Grant Agreement No. 211384. We would like to thank M. Joachimski (GeoZentrum Nordbayern, Erlangen, Germany) for analyses of C and O isotopes. Thanks are due to M. Holcomb (Perth University, Australia) for fruitful discussion and an anonymous reviewer for comments.
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