Bio-Optical Variability in Tropical Peatland-Influenced Coastal Waters of South-East Asia, and Implications for Remote Sensing of CDOM and DOC

South-East Asia accounts for a significant fraction of the global riverine fluxes of dissolved organic matter and suspended sediment to the ocean. These fluxes impact carbon budgets and underwater light attenuation, and may have increased due to land-use change. However, the use of remote sensing for monitoring biogeochemical parameters in coastal waters in South-East Asia is still limited by our poor understanding of the bio-optical variability in this region. We will present bio-optical data from peatland-draining rivers and coastal waters in Sarawak (Borneo) and from a biogeochemical time-series in Singapore. In Sarawak, inputs from different river systems resulted in large spatial variability in bio-optical parameters, with >100-fold variation in CDOM absorption, suspended sediment concentration, backscattering, and particulate absorption. Light absorption budgets were dominated by CDOM and/or non-algal particles, depending on location, with non-algal particle absorption more important close to sediment-rich rivers, while CDOM dominated close to blackwater rivers and at more marine stations. Phytoplankton mostly accounted for <20% of light absorption at all stations. In contrast, bio-optical variability in Singapore was strongly seasonal, owing to the monsoonal changes in ocean circulation. We observed up to 10-fold seasonal variation in CDOM concentration, with a_y(440) ranging from 0.04–0.4 m^-1, reflecting seasonal advection of CDOM from peatlands in Sumatra. Light absorption in Singapore was CDOM-dominated. We will discuss the variability in specific inherent optical properties in both regions, and show that a semi-analytical remote sensing model based on a spectral library constructed from our in-situ measurements can retrieve CDOM and dissolved organic carbon in these optically complex waters.