Vertical profiles of 228 Ra (half-life: 5.75 years) in the ocean provide valuable information on water mixing and ages of the upper ocean. However, its application is hampered by extremely low levels of 228 Ra in the deep ocean. In this study, we measured high-resolution 228 Ra/ 226 Ra ratio profiles (>21 depths) in the East Sea (Japan Sea) by mooring Mn-fiber. Using the measured 228 Ra profile from 228 Ra/ 226 Ra ratios and 2...