BIOOPTICAL OBSERVATIONS OF 1ST-YEAR ARCTIC SEA-ICE

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.