Basal Terraces on Melting Ice Shelves

Abstract:

Ocean waters melt the margins of Antarctic and Greenland glaciers and individual
glaciers' responses and the integrity of their ice shelves are expected to depend on the
spatial distribution of melt. The bases of the ice shelves associated with Pine Island
Glacier (West Antarctica) and Petermann Glacier (Greenland) have similar geometries,
including kilometers-wide, hundreds-of-meter-high channels oriented along and across
the direction of ice flow. The channels are enhanced by, and constrain, oceanic melt.
New, meter-scale observations of basal topography reveal peculiar glaciated landscapes.
Channel flanks are not smooth, but are instead stepped, with hundreds-of-meters-wide
flat terraces separated by 5-50 m-high walls. Melting is shown to be modulated by the
geometry: constant across each terrace, changing from one terrace to the next, and greatly
enhanced on the ~45°-inclined walls. Melting is therefore fundamentally heterogeneous
and likely associated with stratification in the ice-ocean boundary layer, challenging
current models of ice shelf-ocean interactions.