Direct evidence using tritium data for throughflow from the Pacific into the Indian Ocean

Abstract

Basin-wide exchange between the Pacific and Indian oceans through the Indonesian Archipelago has received attention, both in relation to the oceans' role in the Southern Oscillation¹ and in efforts to balance the salt and mass fluxes of the individual basins^2–5. Wyrtki⁶ made the first indirect estimate using hydro-graphic data of a mean annual transport from the Pacific to the Indian Ocean of 2 × 10⁶ m³ s⁻¹ in the upper 200m. Recent estimates have been considerably higher: 14 × 10⁶ m³ s⁻¹ by Piola and Gordon², 10 × 10⁶ m³ s⁻¹ by Godfrey and Golding⁵, and 5 × 10⁶ m³ s⁻¹ by Godfrey and Ridgeway³. However, Wunsch et al.⁴ concluded that, as a result of inverse calculations on sections across the South Pacific, there was a negligible throughflow transport. A meridional maximum in bomb-produced tritium (half-life 12.4 yr) observed in the South Equatorial Current (SEC) of the Indian Ocean is used here to show direct evidence that in the mean there is a net transport (in the upper 300 m) of 5 × 10⁶ m³ s⁻¹ from the Pacific into the Indian Ocean.