Surface distributions of 228Ra in seas and oceans globally: Implications for water circulation and contaminant transport.

ABSTRACT

Seawater movements are challenging to track and monitor for the transport of various soluble materials. Since the 1960s, naturally occurring radium isotopes (Ra), particularly 228Ra, with a half-life of 5.75 y, have provided unique insights into oceanic seawater circulations within a 30 y timescale. Since the 1980s, especially in the 2000s, frequent research expeditions and improvements in analytical techniques have enabled the determination of fine-scale lateral variations in 228Ra/226Ra ratio and 228Ra concentration. These results describe ocean-, sea-, and basin-scale seawater circulations and current mixing, including seasonal variations. Additionally, the source areas of Ra in seawater (i.e., coastal and shallow shelf areas) often overlap with areas containing contaminants released by human activities. Notably, the surface current systems inferred from the distribution of 228Ra closely explained the transport patterns of radiocesium derived from the Fukushima Dai-ichi Nuclear Power Plant. Databases of 228Ra/226Ra ratios and 228Ra concentrations have the potential to predict flow pathways and timescales for various soluble contaminants in ocean and sea environments.