Correlation between δ^(18)O, Sr/Ca and Mg/Ca of coral Acropora and seawater temperature from coral culture experiments

To be used as proxies of seawater surface temperature （SST）, the 61Soc values and Sr/Ca and Mg/Ca ratios of scleractinian coral skeletons must be verified by coral culture experiments in the laboratory. This paper describes a coral culture experiment that was conducted at several seawater temperatures T （21-28℃） using a tandem aquarium system and the new method for depositing coral skeletons grown under controlled conditions. The δ180c values and the St/Ca and Mg/Ca ratios of the cultured coral were measured. We concluded that the δ18Oc values and Sr/Ca and Mg/Ca ratios of the cultured coral are clearly corre- lated with T. The linear regression curve is δ18Oc（‰）=-0.1427×T（℃）-0.1495 （n=18, r=0.955, p〈0.0001）, and the slope of -0.1427‰/°d℃ is at the low end of the range of published values （-0.13-0.29‰/°d℃）. The Sr/Ca ratio decreases with increas- ing T, whereas the Mg/Ca ratio increases with increasing T, indicating a negative correlation between Sr/Ca and Mg/Ca. Their linear regression curves are Sr/Ca（mmol/mol）=-O.O4156×T＋lO.59 （n=15, r=-0.789, p〈0.005） and Mg/Ca （mmol/mol）= 0.04974×T＋2.339 （n=17, r=-0.457, p〈0.05）, respectively, which demonstrate that when Mg/Ca and Sr/Ca are increased by one unit, T increases by 5.19℃and decreases by 15.62℃, respectively. These variations are significantly lower than published values.

To be used as proxies of seawater surface temperature(SST), the δ 18Oc values and Sr/Ca and Mg/Ca ratios of scleractinian coral skeletons must be verified by coral culture experiments in the laboratory. This paper describes a coral culture experiment that was conducted at several seawater temperatures T(21–28°C) using a tandem aquarium system and the new method for depositing coral skeletons grown under controlled conditions. The δ 18Oc values and the Sr/Ca and Mg/Ca ratios of the cultured coral were measured. We concluded that the δ 18Oc values and Sr/Ca and Mg/Ca ratios of the cultured coral are clearly correlated with T. The linear regression curve is δ18Oc(‰)=δ0.1427δT(°C)δ0.1495(n=18, r=0.955, p<0.0001), and the slope of δ0.1427‰/°C is at the low end of the range of published values(δ0.13–δ0.29‰/°C). The Sr/Ca ratio decreases with increasing T, whereas the Mg/Ca ratio increases with increasing T, indicating a negative correlation between Sr/Ca and Mg/Ca. Their linear regression curves are Sr/Ca(mmol/mol)=δ0.04156δT+10.59(n=15, r=0.789, p<0.005) and Mg/Ca(mmol/mol)= 0.04974δT+2.339(n=17, r=0.457, p<0.05), respectively, which demonstrate that when Mg/Ca and Sr/Ca are increased by one unit, T increases by 5.19°C and decreases by 15.62°C, respectively. These variations are significantly lower than published values.