## Materials and Methods
### Field Measurements  
Seven field surveys were performed between 2008 and 2017 (October 2008, January 2011, May 2011, March 2013, November 2016, March 2017, and April 2017; Figure 1 and Table 1). The remote sensing reflectance (\(R_{\mathrm{rs}}\)) and the downwelling diffuse attenuation coefficient (\(K_{\mathrm{d}}\)) were measured in situ, and water samples were collected at the surface (\(\sim\)30 cm) with a standard two-liter polyethylene water-fetching instrument immediately after the optical radiometric measurements. The water samples were stored in the dark at a low temperature (4 \({}^{\circ}\)C) before the laboratory analyses of Chla (\(\mu\)g/L), SPM (mg/L), SPIM (mg/L), suspended particulate organic matter (SPOM, mg/L), and absorption coefficients (m\({}^{-1}\)). Environmental parameters, such as the surface wind speed and cloud conditions, were recorded simultaneously. Laboratory analyses: Chla was measured spectrophotometrically. The water samples were first filtered using Whatman GF/C glass-fiber filters (pore size of 1.1 \(\upmu\)m), and pigments were extracted with 90% acetone. The Chla concentrations were calculated from the absorbances at 630, 645, 663, and 750 nm, which were measured by a Shimadzu UV-2600 spectrophotometer [36]. The SPM concentrations were gravimetrically determined from samples collected on pre-combusted and pre-weighed 47 mm Whatman GF/C glass-fiber filters that were dried at 105 \({}^{\circ}\)C overnight. SPM was differentiated into SPIM and SPOM by burning organic matter from the filters at 550 \({}^{\circ}\)C for 3 h and weighing the filters again [36; 37; 38]. The absorption coefficients of the total particulate matter (\(a_{\mathrm{p}}\)), phytoplankton pigments (\(a_{\mathrm{ph}}\)), and detritus (\(a_{\mathrm{d}}\)) were determined using the quantitative filter technique [39; 40] with 47 mm Whatman GF/C glass-fiber filters and a Shimadzu UV-2600 spectrophotometer. After measuring the total particulate absorption (\(a_{\mathrm{p}}\)), the absorption of the detrital particles (\(a_{\mathrm{d}}\)) was determined from the absorbance measured after the pigments were bleached with sodium hypochlorite, and the difference was the absorption of phytoplankton pigments (\(a_{\mathrm{ph}}\)). The CDOM absorption (\(a_{\mathrm{g}}\)) was determined from filtered water (Millipore filter with a 0.22 \(\upmu\)m pore size) using a Shimadzu UV-2600 spectrophotometer with Milli-Q water as the reference [41; 42]. Remote sensing reflectance (\(R_{\mathrm{rs}}\)): Following NASA protocols [43], the downwelling radiance and upwelling total radiance above the water surface were measured with the above-water measurement method using ASD field spectrometers. A FieldSpec Pro Dual VINR spectroradiometer (350-1050 nm, Analytical Spectral Devices, Inc.) was used to measure the remote sensing reflectance before December 2016, and a FieldSpec Pro HandHeld 2 hand-held spectroradiometer (325-1075 nm, Analytical Spectral Devices, Inc.) was used after. The total water leaving radiance (\(L_{\mathrm{sw}}\)), radiance of the gray panel (\(L_{\mathrm{p}}\)), and sky radiance (\(L_{\mathrm{sky}}\)) were measured to obtain \(R_{\mathrm{rs}}\):  
\[R_{\mathrm{rs}}(\lambda)=(L_{\mathrm{sw}}(\lambda)-r\cdot L_{\mathrm{sky}}( \lambda))/(L_{\mathrm{p}}(\lambda)\cdot\pi/\rho_{\mathrm{P}}(\lambda)) \tag{1}\]  
where \(r\) is the air-water surface reflectance (a value of 2.5% was used), and \(\rho_{\mathrm{P}}(\lambda)\) is the reflectance of the standard reflectance panel. Downwelling diffuse attenuation coefficient (\(K_{\mathrm{d}}\)): The downwelling irradiance (\(E_{\mathrm{d}}(\lambda,z)\)) was measured using a TriOS RAMSES-ARC (Ramses, Germany) with a spectral resolution of 3.3 nm and a sampling interval of 1 nm. Measurements were made from the sunny side of the boat.