Temperature influence on light absorption by fresh water and seawater in the visible and near-infrared spectrum

The influence of temperature on light transmission in the spectral range from 400 to 760 nm has been determined in a two-cell instrument constructed especially for this purpose. Light transmission was measured over a 1-m path length in both a photometric and a spectral mode in double-ion-exchanged fresh water and filtered seawater with a salinity of approximately 25‰. For both groups of samples the temperature-dependence coefficient of the absorption was found to be −0.00091 ± 0.00006 m−1 K−1 in the range from 400 to 550 nm, in contrast to earlier findings. Reproducible signals could be observed only when the samples were left undisturbed for long periods of time between shifts in temperature. The temperature was scanned in alternating directions between 6 and 30 °C in steps of ±2 °C. The time for recording a set of data was between 2 and 3 weeks. Finally, the temperature dependences of the absorption spectra were recorded in the range 400 to 760 nm. These measurements are only partially in agreement with earlier measurements.