## 2 Methods  
Recently, [PERSON] and coworkers refined the models for light scattering by pure water [9], by pure seawater [10,11], and by simple sea salt solutions [12] using the improved measurements of the key thermodynamic parameters, and their models agree with the spectral scattering measurements [13,14] for both pure water and seawater within the experimental errors (2%). Localized fluctuation in density for pure water, as well as additional fluctuations in the mixing ratio of salt ions and water for pure seawater, lead to microscopic inhomogeneities in the refractive index (\(n\)) [15], which in turn cause scattering of light. Since the fluctuations in density and mixing ratio are independent, the scattering coefficient of seawater, \(b\) (m\({}^{-1}\)) can be expressed as  
\[b=b_{d}+b_{c}, \tag{1}\]where \(b_{d}\) represents the scattering due to density fluctuation, and \(b_{c}\) the scattering due to fluctuation of mixing ratio (concentration). Following [PERSON] and [PERSON] [9],  
\[b_{d}=\frac{8\pi^{3}}{\lambda^{4}}(\rho\frac{\partial n^{2}}{\partial\rho})^{2} _{T}kT\beta_{T}h(\delta), \tag{2}\]  
and following [PERSON] et al. [11]  
\[b_{c}=\frac{8\pi^{3}}{\lambda^{4}N_{A}}(\frac{\partial n^{2}}{\partial S})^{2 }\frac{M_{w}}{\rho}\frac{S}{-\partial\ln a_{w}/\partial S}h(\delta), \tag{3}\]  
where, respectively, \(\lambda\), \(k\) (=1.38064852 \(\times\) 10\({}^{-23}\) m\({}^{2}\cdot\)kg\(\cdot\)s\({}^{-2}\cdot\)K\({}^{-1}\)), and \(N_{A}\) (=6.022 \(\times\) 10\({}^{23}\) mol\({}^{-1}\)) are the wavelength of light, the Boltzmann constant, and Avogadro's number; \(\rho\), \(n\), \(T\), \(\beta_{T}\), \(S\), and \(\delta\) are the density, the absolute refractive index, the absolute temperature, the isothermal compressibility, the mass concentration of salts, and the depolarization ratio of the seawater; and \(a_{w}\) and \(M_{w}\) (=18.01528 g mol\({}^{-1}\)) are the activity and molecular weight of pure water. Also, \(h(\delta)=(2+\delta)/(6-7\delta)\). In Equation (1), \(b_{c}\) vanishes for pure water, and the scattering of light is due entirely to density fluctuation. Replacing the density derivative in Equation (2) with pressure derivative, i.e., \((\rho\frac{\partial n^{2}}{\partial\rho})_{T}=\frac{2n}{\beta_{T}}(\frac{ \partial n}{\partial\rho})_{T}\), Equation (2) becomes the Einstein-Smoluchowski equation  
\[b_{d}=\frac{32\pi^{3}}{\lambda^{4}}\frac{n^{2}}{\beta_{T}}(\frac{\partial n}{ \partial P})^{2}_{T}kTh(\delta) \tag{4}\]  
which was used by [PERSON] [6] and [PERSON] et al. [7] in evaluating the temperature dependence of scattering by pure water. Historically, Equation (4) was often used because the isothermal piezo-optic coefficient \((\partial n/\partial P)_{T}\) was relatively easier to measure, even though the uncertainty was high as compared to \(n\)(\(T\)), \(n\)(\(\lambda\)), or \(n\)(\(S\)) [16]. However, recent theoretical development [17] has greatly improved our knowledge in \((\rho\partial n/\partial\rho)_{T}\). This, together with the development of Equation (3) to explicitly account for the effect of salinity on scattering [11], has advanced our capability for modeling scattering by seawater [9; 10; 11], and our confidence in using Equations (1)-(3) to evaluate its temperature effect. The formulae used in the equations to estimate \(n\), \(\rho\), \(\beta_{T}\), and \(a_{w}\) can be found in [PERSON] [9] and [PERSON] et al. [11], and the Matlab code for the model can be accessed at [[https://goo.gl/jkAZgT](https://goo.gl/jkAZgT)]([https://goo.gl/jkAZgT](https://goo.gl/jkAZgT)). Light scattering by seawater is a function of salinity, temperature, and pressure. In this study, we focus on the temperature and salinity ranges of 0-60 \({}^{\circ}\)C and 0-40 psu under one atmospheric pressure, which cover the majority of natural inland, coastal, and oceanic surface water bodies.