Researchers led by Prof. SUN Weidong from the Institute of Oceanology of the Chinese Academy of Sciences (IOCAS) have investigated how oil-drilling affects Ba/Ca ratios in the Porites coral from Weizhou Island in the South China Sea. 

The study was published in Marine Pollution Bulletin. 

The ratio of Ba/Ca in coral is similar to that in seawater. Ba²⁺ appears to substitute readily for Ca²⁺ in the coral aragonite lattice in proportion to the aqueous Ba/Ca ratio. Therefore, the Ba/Ca ratio in coral skeleton reflects the ambient seawater chemistry and can provide a long-term historical record of coral’s environment. 

During the years 1983-1994 and 1996-2002, coral Ba/Ca ratios increased by 12%-17%. Terrestrial input seemed to have small effects on coral Ba/Ca, since precipitation showed no evidence of an increase in coupled with the increase of coral Ba/Ca records. 

The researchers found that the variability in annual coral Ba/Ca values coincided with oil exploration and drilling activities around Weizhou Island. 

"Barite is the main component of waste from offshore drilling platforms and is used as a weighting agent during oil exploration and drilling operations. Ba concentrations in seawater have been shown to increase markedly after drilling activities. This can be recorded in coral Ba/Ca," said Prof. SUN. 

On seasonal timescales, Ba/Ca maxima occurred in the dry season, which differed from the typical coral seasonal peaks in the wet season. "Weizhou Island is situated in the East Asian monsoon area, which has a higher wind speed during winter than summer. Re-suspended sediment on the shelf triggered by the winter monsoon is therefore identified as an important source of coral Ba/Ca peaks," said Dr. LI Xiaohua, first author of the study. "However, the influence of monsoon on annual coral Ba/Ca ratios is minor." 

This study was supported by National Natural Science Foundation of China and the Strategic Priority Research Program (B) of the Chinese Academy of Sciences.