The optical properties of sea ice exhibit considerable spatial, tempor
al, and spectral variability. During a field experiment at Barrow, Ala
ska, we examined the horizontal variability of spectral albedo and tra
nsmittance as well as the vertical variability of in-ice radiance. Tem
poral changes were monitored under cold conditions in April and during
the onset of melt in June. Physical properties, including ice structu
re and concentrations of particulate and dissolved material, were meas
ured to provide a context for understanding the observed temporal, hor
izontal, vertical, and spectral variability in optical properties. For
snow-covered first-year ice in April, wavelength-integrated (300-3000
nm) albedos were high (0.8) and spatially uniform, but there was cons
iderable variability in transmittance. Transmittance at 440 nm ranged
by more than a factor of 2 over horizontal distances of only 25 m, owi
ng primarily to differences in snow depth, although spectral variation
s in transmittance indicate that absorbing organic materials in the ic
e column contribute significantly to the horizontal variability. Peak
values of transmittance in April were 1% near 500 nm, decreasing at bo
th longer and shorter wavelengths. At the onset of melt in June, the i
ce surface rapidly evolved into a variegated mixture of melting snow,
bare ice, and melt ponds. Albedos were much lower and exhibited consid
erable spatial variability, ranging from 0.2 to 0.5 over distances of
a few meters concomitant with the variation in surface characteristics
. Transmission increased over the spring transition as surface charact
eristics evolved to decrease albedo and as in-ice structure was altere
d by heating to reduce attenuation within the ice. The exception to th
is trend occurred over a period of a few days when an algal bloom deve
loped on the underside of the ice and transmission was significantly r
educed. Variability in the in-ice spectral radiance values was observe
d between nearby sites in both first-year and multiyear ice. While the
radiance measurements are strongly dependent on the incident solar ra
diance, under similar solar conditions there was an observed shift in
the peak of the maximum in the spectral radiance from 460 nm in clean
ice to between 500 and 550 nm in ice that contained particulates in th
e surface layer. More impressive spectral shifts were found in an old
melt pond that had accumulated particles at its base. Not only was the
re a strong shift in the spectral nature of the radiance as a function
of horizontal distance, but there also existed large changes vertical
ly within tf ie ice. The vertical variability in the radiance attenuat
ion coefficient was spatially coherent with variations in both the phy
sical structure of the ice, especially grain size, and the concentrati
ons of particulate and dissolved materials entrapped in the ice. Not s
urprisingly, the short-lived algal layer on the underside of the ice r
esulted in changes in the radiance attenuation coefficient from approx
imately 1 m(-1) in the interior ice to approximately 40 m(-1) within t
hat layer.