ABSTRACT. Kau Bay, Halmahera, Indonesia is a small marine basin that is separated from the adjacent SW Pacific Ocean by a shallow sill, 40m deep. Radiocarbon dating on piston cores in combination with a study on microfossils demonstrate that Kau Bay was a freshwater lake in Weichselian times. At 10,000 BP, the Bay became reconnected with the open ocean. If sill depth did not change in the intervening years, sea level at 10,000 BP stood 40m below the present level.