Coralline Ba/Ca ratios and luminescent line records in Con Dao Island, offshore Vietnam, as indicators of Mekong river runoff between 1948 and 1999

Abstract

The Ba/Ca ratios and luminescent lines recorded in coral skeleton in near-shore corals are reflected by fresh river flows. This paper shows 52-year Ba/Ca ratios and bright luminescent lines recorded in coral Porites in the Con Dao Island area, offshore Vietnam, about 90 km from the mouth of the Mekong River. Bright luminescent lines and Ba/Ca ratios are cyclical and formed annually, where the bright luminescent lines and the highest Ba/Ca ratios are simultaneously formed. The measured Mekong River discharge (MRD) and salinity data recorded during the 1985-1999 period show that the annual maximum MRD and minimum salinity in Con Dao Island were synchronous, and that the annual maximum Ba/Ca ratio was formed during maximum MRD and minimum salinity. When the annual minimum MRD and salinity were stable, the annual minimum Ba/Ca ratio was variable. Overall, the mean annual MRD and Ba/Ca ratio slightly decreased during the 1985-1999 period, suggesting that the Ba/Ca ratio is mainly controlled by MRD. The decreasing trend in Ba/Ca ratios over the period between 1948 and 1999 is probably related to the MRD reduction due to human activities and/or climate change.