HAWAII MR1 side-scan sonar and six-channel seismic reflection data reveal a history of carbonate platform growth, drowning, and back stepping in the Huon Gulf, Papua New Guinea. This is one of the few modern sites where active carbonate platform development and foredeep subsidence are linked. 230Th methods date aragonitic shallow-water corals, recovered from a modern depth of 2000 m, at 348 ± 10 ka. This documents rapid subsidence of the Huon Gulf in response to the encroaching Finisterre Mountains at an average rate of 5.7 mm/yr for the past 348 k.y., the highest subsidence rate reported from any foredeep setting. Carbonate deposition has moved toward the foreland at an average rate of 110 mm/yr over the same period. Comparisons of the measured age with sea-level history (derived from the oxygen isotope record) suggest that the reefs may have formed during sea-level lowstands and drowned during rapid rates of sea-level rise.