Mekong river discharge and the east asian monsoon recorded by a coral geochemical record from Con Dao Island, Vietnam

Abstract

The offshore flow of the Mekong River is strongly governed by the East Asian monsoon (EAM). Monthly-resolved skeletal carbonate Sr/Ca, Ba/Ca and oxygen isotope (d18Oc) data from 1980 to 2005 of a Porites coral from Con Dao Island, ~90 km from the Mekong River mouth, were analyzed for capturing the past flood events and the signal of East Asian winter monsoon. Ba/Ca time series is characterized with intra-annual double peaks, the first large one in March during the dry season and relative small one in August during the wet season. The low values of seawater d18O (d18Osw), deduced from both the Sr/Ca ratio and d18Oc, in the wet season resulted from precipitation and/or freshwater input from the Mekong River. The difference in the seasonal characteristics of Ba/Ca and d18Osw between flood and no-flood years could be attributed to the seasonal reversal of the regional ocean current derived from the EAM.