The interrelationships among snow cover, ice structure, optical proper
ties, and biological activity are of critical importance in understand
ing the response and behavior of sea ice systems. Of particular concer
n in this regard are the optical properties of the algae and the effec
t of snow thickness on biomass accumulation. In this paper we present
the first direct in situ measurements of biomass specific diffuse atte
nuation spectra for arctic ice algae. The data show in situ attenuatio
n values that are about 3 times larger than those obtained from corres
ponding in vivo absorption measurements, apparently reflecting differe
nces in the geometrical distribution of the algae or the influence of
skeletal ice and dissolved organic material. Observations also confirm
that maximal algal accumulation occurs when there is a thin layer of
snow covering the ice. A new technique to separate the effects of snow
and algae in observed transmission spectra is presented. The ratio of
transmittance between 600 nm and 450 nm is a sensitive indicator of b
iomass, while the 700 nm to 600 nm ratio is strongly affected by snow
depth.