| Summary: | In connection with phytoplankton studies, a non-optical, non-electric instrument has been devised for the measurement of relative light intensity in sea-ice bore holes. When used with a sensitive photometer, absolute values for the ambient light field can be determined within and immediately under the ice. As anticipated, attenuation is greatest at the ice-air interface; values just below the ice surface were 3 to 20% of incident. Another 70 to 100 cm of ice was required to effect a further 50% decrease in illumination. Extinction values were also measured on the ice cores in the laboratory, but scattering greatly complicates the interpretation of laboratory results.
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