Photosynthetic life is not expected at the Martian poles, but the data reveal the apparently favourable radiation environment for life within the polar caps

An interesting paper from the last polar conference. According to the authors 30 cm of snow (and presumably ice) would reduce DNA damage on living organisms to no worse than Earth. Also the amount of sunlight penetrating is still sufficient for photosynthesis.

"Convolved with a simple Mars radiative transfer
model, the data suggests that under ~6 cm of Martian
snow, DNA-damage would be reduced by an order of
magnitude [2]. Under approximately 30 cm of snow,
DNA damage would be no worse than that experienced
at the surface of the Earth. Although we do not
know the exact characteristics of Martian snows, these
first-order data suggest that burial in even modest coverings
of Martian snows could allow for the long-term
survival (and if water if present, even growth) of contaminant
microorgannisms at the Martian polar caps
even under the extreme UV fluxes of clear Martian
skies. These coverings of snow will also allow for enhanced
preservation of organics against UVdegradation.
Intriguingly, at the depth at which DNA damage is
reduced to similar levels as those found on the surface
of present-day Earth, light levels in the photosynthetically
active region (400 to 700 nm) are still two orders
of magnitude higher than the minimum required for
photosynthesis, showing that within snow-pack on
planets lacking an ozone shield, including Mars, UV
damage can be mitigated, but light levels are still high
enough for organisms that have a requirement for exposure
to light for their energy needs. Photosynthetic
life is not expected at the Martian poles, but the data
reveal the apparently favourable radiation environment
for life within the polar caps."