We discuss recent measurements of the wavelength-dependent absorption coefficients in deep South Pole ice The method uses transit-time distributions of pulses from a variable-frequency laser sent between emitters and receivers embedded in the ice. At depths of 800-1000 m scattering is dominated by residual air bubbles, whereas absorption occurs both in ice itself and in insoluble impurities. The absorption coefficient increases approximately exponentially with wavelength in the measured interval 410-610 nm At the shortest wavelength our value is approximately a factor 20 below previous values obtained laboratory, ice and lake me: with increasing wavelength the discrepancy with previous measurement8 decreases. At ~ 415 to ~ 500 nm the experimental uncertainties are small enough for us to resolve extrinsic contribution to absorption in ice; submicrometer dust particles contribute by an amount that increases with depth and corresponds well with the expected increase seen near the Last Glacial Maximum m Vostok and Dome C ice cores. The laser pulse method allows remote mapping of gross structure in dust concentration as a function of depth in glacial ice.#1997 Optical Society of America
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