The onset of widespread barrier reef development in the Coral Sea region is thought to have occurred during the period 400-1000ka. Whether the timing of reef inception was limited by either global or regional climatic changes remains unresolved. Here we present a new set of paired down-core foraminiferal δ¹⁸Oplanktic - Mg/Ca measurements from the southeastern boundary of the modern West Pacific Warm Pool (core MD06-3018, 2470m water depth, 23°S, 166°E in the New Caledonia Trough) that span the past 1000ka at ~5kyr resolution. If it is assumed that glacial-interglacial variations in sea surface salinity only exert a negligible effect on Mg/Ca ratios then past δ¹⁸Oseawater values may be calculated from the paired δ¹⁸Oplanktic - Mg/Ca measurements. The component of δ¹⁸Oseawater variability not attributable to global ice volume changes must originate from changes in the regional hydrological cycle. The MD06-3018 records suggest that prior to MIS 15 (~600ka) interglacial conditions were in general both cooler and fresher (light δ¹⁸Oseawater values) than those before it. Such a transition from relatively cool and fresh to relatively warm and salty interglacial stage surface waters may have been caused by a southward expansion of the influence of West Pacific Warm Pool waters and is consistent with a climatic control on reef inception.