An empirical ocean color algorithm for estimating the contribution of chromophoric dissolved organic matter to total light absorption in optically complex waters

To estimate the depth-integrated rate of photochemical processes involving chromophoric dissolved organic matter (CDOM) in coastal waters, the contribution of CDOM to the total absorption coefficient must be known from UV to green. At 307 sites sampled in various coastal marine environments, the ratio between CDOM and the total absorption coefficient ([a(CDOM/)a(t)]) at 412 nm was found to vary over a wide range, from 0.20 to 0.95. An empirical algorithm was developed to retrieve [a(CDOM)/a(t)](412) from satellite remote sensing reflectance. The absolute uncertainty on the [a(CDOM)/a(t)] retrieval was 0.14. As exemplified with the data from the Baltic and North Seas, the algorithm provides a means to distinguish the contribution of CDOM to the absorption coefficient of colored detrital material (i.e., CDM = CDOM + nonalgal particles) at the regional scale. The implications of the variability in the magnitude and spectral shape of [a(CDOM)/a(t)] for the assessment of depth-integrated production of any photoproducts involving CDOM photolysis are discussed in details. We applied the algorithm to a Sea-viewing Wide Field-of-View Sensor (SeaWiFS) image of the Southeastern Beaufort Sea where terrestrial inputs are abundant. The spatial variability in the [a(CDOM)/a(t)] reaches as much as threefold over the continental shelf and beyond. These results clearly show that it is necessary to account for the spatial variability of [a(CDOM)/a(t)] when quantifying CDOM-related photochemical processes in the ocean.