Seasonal Distribution of Observed Colored Dissolved Organic Matter (CDOM) in the Eastern Indian Ocean

Colored dissolved organic matter (CDOM) is a crucial constituent that affects the optical absorption properties of seawater. Owing to the relatively limited measured data on the spatial distribution characteristics of CDOM in the tropical eastern Indian Ocean, this study analyzes the optical absorption characteristics of CDOM in the southeast Indian Ocean using the data collected during four seasons from 2013 to 2017. This work also systematically describes the seasonal horizontal and vertical distribution characteristics of CDOM in this area and conducts a preliminary analysis of the relevant factors affecting CDOM absorption characteristics in this region. Results indicate that the CDOM ag(440) during summer was remarkably lower than that in the coastal waters of Europe and coastal waters of China but slightly higher than that in the western and southeast Pacific. The spatial distribution of surface CDOM shows remarkable seasonal differences, and the spatial distribution characteristics of CDOM in the 5°S, 92°E region differ between spring/summer and autumn/winter. The values of ag(400) and ag(440) are weak/strong at a surface/subsurface level of 100 m, with differences found between summer and winter. The correlation of CDOM with temperature, salinity, and chlorophyll-a concentration is relatively low, indicating that CDOM is an independent driving mechanism influenced by phytoplankton degradation, photobleaching, and water mixing.