Dissolved organic carbon in the INDEX area of the Central Indian Basin

Dissolved organic carbon (DOC) concentrations at the Indian Deep-Sea Environment Experiment (INDEX) site of the Central Indian Basin can be divided into three depth intervals. The subsurface layer (25–200 m) shows highly variable distribution with concentrations ranging from 52 to 191 μM. Between 500 and 800 m, DOC shows a minimum (41–57 μM) and is associated with decreased oxygen. The bottom waters (3500–5300 m) show decrease with little variability in the DOC concentrations (41–64 μM) suggesting its refractory nature in the deep ocean. The variable concentration of DOC with depth is related to the biochemical activity as well as to the chemical features of the water column. Both high and low values of DOC with high apparent oxygen utilisation (AOU) indicate no significant correlation between DOC and AOU and suggest simultaneous utilisation of oxygen for the oxidation of other species of organic matter in the water column.