Plain Language Summary: We used a novel method to image through the Larsen C Ice Shelf, Antarctica, at a suture zone, where two ice masses merge. We discovered two distinct layers: a 300‐m‐thick upper layer of dense, impermeable ice likely formed from compacted snow, and a thinner layer of porous, frozen seawater. The latter marine ice layer at the base of the ice shelf is less dense than that of a basal marine ice layer observed at a location 195 km downstream. This suggests the basal layer consolidates as it flows toward the ocean. Understanding this layered structure is essential for predicting the ice shelf's stability.