A transform boundary forms the northern border with the Pacific plate.

Along the border with the Philippine Sea plate is a convergent boundary that transitions into a rift.

The Caroline-Pacific boundary is a complex, evolving system partly and potentially developing into a subduction zone.

The presence of a trench and indications of subduction beneath the Pacific plate is suggestive but the absence of island arcs, which could be expected from substantial subduction in the past, makes the development along this boundary unclear.

[6] Before about 6 million years ago as the Ontong Java Plateau and Indo-Australian plate collided the Bismarck Sea was initially formed as a back-arc basin behind the New Britain arc, and after the collision, a transpressional zone developed in what is now the west Bismarck Sea, associated with subduction of the Caroline plate and North Bismarck plate at the New Guinea Trench.