Table 1 Radium-228 sources and sinks (all in 1022 atoms year−1) in the Arctic surface ocean.

The shelf flux was determined by difference, assuming that, at steady state, the sources of 228Ra to the surface layer must be balanced by sinks. The best estimate for each term was used in the mass balance calculation; see Materials and Methods for details on how the minimum and maximum flux estimates were determined.

SinksBest-estimate flux (1022 atoms year−1)Minimum flux (1022 atoms year−1)Maximum flux (1022 atoms year−1)% of total sinks
Decay8.26.69.955
Advection6.85.41645
SourcesBest-estimate flux (1022 atoms year−1)Minimum flux (1022 atoms year−1)Maximum flux (1022 atoms year−1)% of total sources
Ice-rafted sediment0.0890.0120.40<1
Advection2.21.43.115
Rivers0.550.200.994
Shelf127.52581