In the South Pacific Ocean, upper and lower Circumpolar Deep Water (UCDW and LCDW, respectively) occupy the deep layers; however, the presence and fate of both these water masses in the western equatorial Pacific have been mostly based on sparse measurements in both space and time. In this study, unprecedented deep measurements from three cruises conducted in the Solomon Sea region along with the World Ocean Atlas 2018 database are examined to better characterize the properties and pathways of deep water in the Southwest Pacific. At depths encompassing most of the UCDW, estimated transports derived from two inverse model solutions indicate interbasin exchanges between the Solomon Sea Basin and the Coral Sea Basin to the south and the East Caroline Basin to the north. The deep water transport variability found across the Solomon Sea is consistent with observed water mass modifications due, for the most part, to diapycnal mixing. At depths greater than about 2600 m, deep water inflow into the Solomon Sea Basin is limited to the south, emanating from the Coral Sea remote basins via complex trench topography. Spreading of LCDW in the Coral Sea and subsequently into the Solomon Sea is blocked by the Tonga-Kermadec Ridge to the east and bottom topography to the south, however, the densest part of UCDW entering both the Coral and Solomon Seas is likely influenced by LCDW properties, as oxygen is found to increase and silicate decrease with depth in the region. Waters trapped in closed deep basins, in the Bismarck Sea below 1750 m and the northern Solomon Sea below 3500 m show a remarkably constant pattern in oxygen with depth.