We have re-assessed the Sr isotopic budget of the modern ocean taking into account the high erosion rates of volcanic islands, and especially of island arcs, emphasizing important contribution from subsurface weathering to global budgeting. We propose that intensive weathering on volcanic islands, island arcs and oceanic islands, coupled with large surface and subsurface water fluxes is the missing source of mantlederived 87Sr/86Sr (0.703) in seawater Sr isotope balance. In our approach, it represents 60% of the actual mantle-like input of Sr to the oceans, the remaining 40% supplied by ridge-crest hydrothermal activity and sea-floor low-temperature alteration of basalts. The seawater Nd isotopic budget is consistent with this interpretation and explains well the regional contributions from ridge crest and island arc activity among the oceans.