Effect of salinity on the skeletal chemistry of cultured scleractinian zooxanthellate corals: Cd/Ca ratio as a potential proxy for salinity reconstruction

Abstract

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

Evidence for the non-influence of salinity variability on the <i>Porites</i> coral Sr/Ca palaeothermometer

“…Results presented in this study are in agreement with previous laboratory investigations from Zhong and Mucci (1989) which concluded that for synthetic aragonite precipitated in seawater solutions of various salinities (from 5 to 44 psu), the incorporation of Sr 2+ is unaffected by salinity variations. Our results are also in agreement with the recently published work of Pretet et al (2013), who investigated the effect of salinity on the skeletal chemistry of cultured corals Acropora sp., Montipora verrucosa and Stylophora pistillata. The three coral genera were bred in three different aquaria with artificial seawater and at a salinity of 36, 38 and 40 psu, respectively.…”

“…Nevertheless, these studies were rather local and did not encompass a large salinity range. A recent laboratory experiment based on three different coral genera (Acropora sp., Montipora verrucosa and Stylophora pistillata) found no effect of salinity (in the range 36-40 psu) on Sr / Ca, but this study did not encompass the Porites genus (Pretet et al, 2013).…”

“…The three coral genera were bred in three different aquaria with artificial seawater and at a salinity of 36, 38 and 40 psu, respectively. Although Pretet et al (2013) did not work with Porites spp. and had a smaller salinity range, they reached similar conclusion; Sr / Ca and other elemental ratios (Mg / Ca; Li / Ca; U / Ca) measured in the coral skeleton do not vary with salinity changes.…”

Acropora interbranch skeleton Sr/Ca ratios: Evaluation of a potential new high‐resolution paleothermometer

“…Following the release of the Fourth and Fifth Assessment Reports of the Intergovernmental Panel on Climate Change the scarcity of paleoclimate data representing tropical marine environments and the southern hemisphere has become increasingly clear [e.g., Intergovernmental Panel on Climate Change , ; Masson‐Delmotte et al , ]. Of the available high‐resolution paleoclimate records, coral colonies are particularly useful because skeletal geochemistry can provide subannual time series data on past water temperature [ Bagnato et al , ; DeLong et al , ; Epstein et al , ; Gagan et al , ; Grottoli and Eakin , ; McCrea , ], salinity [ Corrège , ; Felis et al , ; Gagan et al , ; Hendy et al , ; Le Bec et al , ; Pretet et al , ; Wu et al , ], pH [ Hemming and Hanson , ; Pelejero et al , ; Shinjo et al , ; Wei et al , ], and nutrient concentration [ LaVigne et al , , ]. On a global scale, such proxy data can help unravel Earth's natural climate variability and therefore improve computer model predictions of future climate.…”

Coral Microcosms: Challenges and Opportunities for Global Change Biology

“…Slightest unintended variations in water parameters can cause significant effects to reef organisms [71][72][73][74]. Therefore, high-quality seawater is an important prerequisite for ensuring meaningful and comparable results in experimental systems [20,26].…”