The western boundary of the tropical Pacific is not continuous, and leakage of low-frequency energy from the Pacific to the Indian Ocean is possible. At low frequencies, equatorial Kelvin and Rossby waves have very large east-west scales compared with the east-west scale of the land masses in the region. Consequently, these land masses may be treated as islands that are infinitesimally thin in the east-west direction. By generalizing previous theory for a single island, the leakage and multiple reflection of low-frequency energy through the seven major ''islands'' forming the boundary of the western Pacific can be studied. The results obtained depend on continuity of mass and large-scale balances and not on the details of nonlinear and/or frictional flow near island eastern boundaries. The major results are as follows: (1) When a mode 1 low-frequency Rossby wave is reflected at the discontinuous western Pacific boundary, the eastward reflected Kelvin wave energy flux is about one third of the incoming energy flux, or about two thirds of that expected for a solid meridional wall. In other words, the reflected Kelvin wave amplitude is 83% of that which would be reflected from a solid meridional wall. The reflection mainly occurs from the Indonesia/Borneo/Asia land mass and very little energy gets into the Indian Ocean. (2) Sea levels in the western equatorial Pacific and on the western boundaries of the major western Pacific land masses should be in phase and of a similar amplitude. In particular, in-phase interannual sea levels should occur along Australia's western coast and be highly correlated with sea levels in the western equatorial Pacific. Sea level data at Truk Island and on Australia's western coastline confirm this prediction.

(3) The interannual exchange of water between the Pacific and Indian oceans due to interannual oscillations in the Pacific is about 6 Sv (1 Sv=106 m3 s-1), is highly correlated with El Ni¿o/Southern Oscillation (ENSO) events, and bears definite phase relationships to sea level stations at locations in the western Pacific. For example, for a high sea level at Darwin, the transport is westward from the Pacific Ocean into the Indian Ocean. It seems that interannual transport may be approximately monitored using coastal sea level. (4) Strong narrow low-frequency currents are predicted to occur westward of some island tips. (5) Interannual Indian Ocean Kelvin wave signals are largely blocked at the Indonesia/Borneo/Asia land mass. (6) In terms of net transport, reflection, and transmission properties, the seven island Pacific western boundary can be reduced to a simpler two-island problem, in which one island is the Indonesia/Borneo/Asia land mass and the other New Guinea/Australia. (7) The comparatively small Halmahera Sea between Halmahera and New Guinea is dynamically important. Closing this sea for the incident first meridional mode Rossby wave case reduces the interannual transport between the Pacific and Indian Oceans by 40%. ¿1991 American Geophysical Union