Abstract

The temperature and salt dependencies of absorption by liquid water $\left({\text{H 2}}_{}\text{O}\right)$ and heavy water $\left({\text{D 2}}_{}\text{O}\right)$ were determined using a hyperspectral absorption and attenuation meter (WET Labs, AC-S). Sodium chloride (NaCl) was used as a proxy for seawater salts. There was no significant temperature $\left({\Psi }_T\right)$ or salt $\left({\Psi }_S\right)$ dependency of absorption at wavelengths $<550\text{\hspace{0.17em} nm}$. At wavelengths $>\text{550 nm}$, ${\Psi }_T$ exhibited peaks at $\sim 604$, 662, and $740\text{\hspace{0.17em} nm}$. A small negative trough in ${\Psi }_S$ occurred at $\sim 590\text{\hspace{0.17em} nm}$, followed by a small positive peak $\sim 620\text{\hspace{0.17em} nm}$, a larger negative trough at $\sim 720\text{\hspace{0.17em} nm}$, and a strong positive peak at $\sim 755\text{\hspace{0.17em} nm}$. The salt dependency of absorption by heavy water, ${{\Psi }_s}^H$, exhibited a negative power-law shape with very low ${{\Psi }_s}^H$, at wavelengths $>550\text{\hspace{0.17em} nm}$. Our experiments with NaCl, clean open ocean seawater, and artificial seawater support the hypothesis that salts modify the absorption spectra of seawater by modifying the molecular matrix and vibrations of pure water.

© 2006 Optical Society of America

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