Geochemical characteristics of Kau Bay water

Abstract

Water in Kau Bay (Halmahera, Indonesia) differs chemically and physically from the water in the adjacent Pacific Ocean. Ventilation of the bay, with a maximum depth of 480 metre, is restricted by the presence of a sill at the entrance of the bay at a depth of 40 metre. Because of this restriction bottom waters in the deepest part of the bay become almost anoxic due to the complete consumption of oxygen by microbial degradation of labile organic matter. Suboxic mineralization of organic matter at the sediment-water interface brings about a flux of dissolved manganese into the bottom water, where it is re-oxidized and precipitated by microbial mediation into particulate manganese oxides. The profile of dissolved ΣPO 4 displays an almost perfect image of the O 2 profile. The Si profile shows a continuous increase with depth. The chemical profiles all point at a transient state of the water column. The profiles of a few redox-sensitive ionic species (UO 2 2+, V, Sb 3+/Sb 5+, As 3+/As 5+) show some relation with the oxygen profiles, but are probably to a large extent coupled with fluxes and mineralization of organic matter in the water column.