Abstract
Ice streams deposit sediment at their grounding lines, where ice reaches
flotation. Grounding Zone Wedge (GZW) deposits indicate standstills in
past grounding-line retreat, and are thought to stabilize grounding
lines by reducing local water depth, restricting ice flow. However, the
mechanisms of GZW growth are uncertain, as are the effects of
sedimentation on a retreating grounding-line prior to GZW formation. We
develop a 1-D coupled model of ice flow and sediment transport,
considering both subglacial deposition of deforming sediments, and
proglacial melt-out of entrained sediments from ice shelves. A refined
grid near the grounding line resolves small sediment features and their
effect on ice dynamics. The model simulates the growth of low-profile,
prograding, asymmetric features consistent with observed GZWs. We find
that the characteristic shape of GZWs arises from the coupling of
sedimentation and ice dynamics. This mechanism is consistent with
deposition from either deforming or entrained sediments, and does not
require a low-profile ice shelf to limit vertical GZW growth. We also
find that during grounding-line retreat, sedimentation provides a
stabilizing feedback when other factors initially slow retreat. This may
turn a slowdown in retreat into a long standstill, even when ice
dynamics are far out of equilibrium. The feedback depends on total
sediment flux and its spatial pattern of deposition, making these
priorities for future study. Our study suggests that sedimentation might
significantly extend pauses in deglaciation, and the model provides a
new tool for exploring links between ice-stream dynamics and submarine
landforms.