| Summary: | We evaluated six empirical and semianalytical models of the diffuse attenuation coefficient at 490 nm (<i>K<sub>d</sub></i>(490)) using an in situ dataset collected in the Pearl River estuary (PRE). A combined model with the most accurate performance (correlation coefficient, <i>R</i><sup>2</sup> = 0.92) was selected and applied for long-term estimation from 2003 to 2017. Physical and biological processes in the PRE over the 14-year period were investigated by applying satellite observations (MODIS/Aqua data) and season-reliant empirical orthogonal function analysis (S-EOF). In winter, the average <i>K<sub>d</sub></i>(490) was significantly higher than in the other three seasons. A slight increasing trend was observed in spring and summer, whereas a decreasing trend was observed in winter. In summer, a tongue with a relatively high <i>K<sub>d</sub></i>(490) was found in southeastern Lingdingyang Bay. In Eastern Guangdong province (GDP), the relatively higher <i>K<sub>d</sub></i>(490) value was found in autumn and winter. Based on the second mode of S-EOF, we found that the higher values in the eastern GDP extended westward and formed a distinguishable tongue in winter. The grey relational analysis revealed that chlorophyll-a concentration (<i>C<sub>chla</sub></i>) and total suspended sediment concentration (<i>C<sub>tsm</sub></i>) were two dominant contributors determining the magnitude of <i>K<sub>d</sub></i>(490) values. The <i>C<sub>tsm</sub></i>-dominated waters were generally located in coastal and estuarine turbid waters; the <i>C<sub>chla</sub></i>-dominated waters were observed in open clear ocean. The distribution of constituents-dominated area was different in the four seasons, which was affected by physical forces, including wind field, river runoff, and sea surface temperature.
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