Abrading Dunes in the North Polar Erg (natural colors; credits: Lunexit)

This location is where Mars Global Surveyor (a.k.a.: MGS) saw evidence of dunes that either shrank or completely disappeared over a span of a few years. HiRISE provides new details at higher resolution.
As seen here, the dunes show clear evidence of erosion.
Based on the shape of the dunes in this picture, the strongest winds have blown from the upper right (South-East) to lower left (North-West).
Streamers of dark sand are visible on the white, frost-covered surface downwind of the dunes. This is particularly prominent at the “horns” of the barchan dunes (these are the dunes with the prominent points at their edges).

Scientists believe these dunes are cemented, by ice, such that the wind is progressively eroding them over time. Future observations by HiRISE will determine if the dunes shrink as indicated by MGS, or maybe even migrate, over time.