Abstract

Icebergs are hardly colorless monoliths, and even nominally white bergs routinely display many hues.¹-³ However, satisfactorily accounting for vivid bottle-green icebergs⁴-⁸ has proven to be an elusive goal. Obviously, the colors of some sea and glacier ice are caused by intrinsically colored⁹ minerals or organisms.¹⁰-¹² Yet ice recently taken from (or near) green icebergs indicates that they may not be dominated by green inclusions. Amos reported that an unusual ice sample taken near a green iceberg was “remarkably bubble-free” and included "a large number of fibers …ranging from colorless to blue, orange, and green; obsidian flakes; a few quartz grains; amorphous aggregates; black, charcoal-like fragments; pieces of shelly material; and diatoms …."⁷ Dieckmann et al. sampled a green iceberg in the Weddell Sea, and they found ice containing "grey mineral and biogenic material apparently of marine origin" distributed in “relatively well defined layers" throughout.⁸ They reached the same tentative conclusion as Amos, holding that: "Our analyses and observations confirm that the green colouration was not caused by green pigmentation, but probably by reflection and/or absorption of light due to the more or less densely spaced, parallel layers of incorporated debris. Green feldspars which could have been responsible for the colour were rarely found. "⁸ They also note that their ice block "changed from green to a translucent white upon separation from the iceberg. "⁸ (Gerhard Dieckmann kindly provided me with some original color slides of this green iceberg.)

© 1990 Optical Society of America