ABSTRACT

Deltaic sediments of the Mekong River delta sampled from a tidal beach in Vietnam during the wet season (late October 2011) showed strong ¹³⁷Cs and ¹³⁴Cs activities reflecting radionuclides released from the Fukushima Dai-ichi nuclear power plant (FDNPP) after the March 2011 Tohoku-oki earthquake and tsunami, but samples from the same site taken about three months later during the dry season (early February 2012) showed weak activities. This finding indicates that soil from the Mekong drainage basin was deposited along the delta front in the wet season and then removed in the dry season during the winter monsoon. Thus, seasonal changes in the sedimentary environment of sediment supply and accumulation were elucidated by Cs isotopes from the FDNPP accident. This finding may expand the usefulness of radionuclides for obtaining important information about geochemical events.