āCā and āDā means a triangle node on the coastline corresponding to
Fig. S1.
For stations C1-C18, the radium activities and salinity at each triangle
node on the coastline were approximated by those at the nearest seawater
station and the water depths at these nodes are set to be zero.
For stations D1-D4, 18O value, 228Ra
activity, salinity and depth of these triangle nodes were calculated
based on the distance-weighted method. The distance is between the
triangle node and corresponding two or three near seawater stations.