Temperature control on high-resolution SIMS oxygen isotopic compositions in Porites coral skeletons

Oxygen isotope composition (delta O-18) in Porites coral skeletons at the micrometer scale has been proposed to be uninfluenced by temperature in previous studies. Considering that temperature is the main controlling factor of coral delta O-18 at the macro scale, the effect of temperature on the delta O-18 variations at the micrometer scale should be evaluated carefully. To better understand the climatic and biological significance of high-resolution delta O-18 in coral skeletons, in situ delta O-18 values were analyzed in three modern Porites corals from the South China Sea and the Great Barrier Reef by a Cameca IMS 1280-HR secondary ion mass spectrometry (SIMS). A twice vacuum impregnation procedure for sample mount preparation and a subsection calibration method based on multiple controlling points for coral matrix effect correction were used for SIMS analysis. The derived SIMS coral delta O-18 time series exhibit consistent long-term variations with the monthly delta O-18 (measured by conventional gas isotope ratios mass spectrometry), monthly Sr/Ca, and daily sea surface temperature, first highlighting the dominant temperature control on micrometer-scale coral delta O-18. The 1.5 parts per thousand fluctuation amplitude of SIMS coral delta O-18 at the scales of 400-800 mu m can be explained by the combined SST effects of similar to 10-day variation and day-night fluctuation, whereas the effects of seawater delta O-18 and growth rate on SIMS coral delta O-18 seem not dominant. Some abnormally negative delta O-18 values possibly resulted from the primary ion bombardment on indistinguishable centers of calcification. Copyright (C) 2021, Guangzhou Institute of Geochemistry. Production and hosting by Elsevier B.V.

Automated summary

High-resolution delta O-18 values in coral skeletons were analyzed using secondary ion mass spectrometry in Porites corals from the South China Sea and the Great Barrier Reef. The results showed that temperature has a significant effect on micrometer-scale coral delta O-18 variations, while the effects of seawater delta O-18 and growth rate were found to be minor. Abnormally negative delta O-18 values could be attributed to ion bombardment on calcification centers.