Are seasonal deposits in spring at the Martian North Pole much shallower
than previously thought?
The seasonal deposition and sublimation of CO2 constitute a major
element in the Martian volatile cycle. Here, we propose to use the
shadow variations of the ice blocks at the foot of the steep scarps of
the North Polar Layered Deposits (NPLDs) to infer the vertical evolution
of the seasonal deposits at high polar latitudes. We conduct an
experiment at a steep scarp centered at (85.0°N, 151.5°E). We show that
the average thickness of the seasonal deposits due to snowfalls in Mars
Year 31 is 0.97±0.13 m at Ls = 350.7° in late winter, which then
gradually decreases in springtime. The large snow depth measured makes
us wonder if snowfalls are more frequent and violent than previously
thought. Meanwhile, we show that the average frost thickness due to
direct condensation in Mars Year 31 reaches 0.64±0.18 m at Ls = 350.7°
in late winter and quasi-linearly decreases towards the summer solstice.
Combined, the total thickness of the seasonal cover in Mars Year 31
reaches 1.63±0.22 m at Ls = 350.7° in late winter, continuously
decreases to 0.45±0.06 m at Ls = 42.8° in middle spring and 0.06±0.05 m
at Ls = 69.6° in late spring. These estimates are up to 0.8 m lower than
the existing MOLA results during the spring, which can be mainly
attributed to MOLA-related biases. In terms of interannual variations,
we observe that snow in the very early spring of Mars Year 36 can be
0.36±0.13 m deeper than that in Mars Year 31.