Measurements of the inherent optical properties were collected during the summer of 1998 above the Chukchi Plateau. These measurements show that attenuation by particles is sometimes very low, but absorption by colored dissolved organic materials (CDOM) is generally high, so the waters of the study site should not be considered to be among the clearest natural waters. The CDOM increases the absorption of shortwave radiation between 350 and 700 nm by over 30% in the top 10 m when compared to the clearest natural waters. Optical properties representative of those measured during phytoplankton blooms show that heating of the top 10 m can increase substantially during blooms. The increased absorption near the sea surface provides more heat for melting the bottom of the ice than previous models have assumed.