Fig. 9: Conceptual illustration of the proposed mechanism to create variable accumulation across a shallowing surface around the grounding zone of an ice shelf.

Ice flows from left to right, accumulating as it flows along a concave-upwards surface trajectory (thick grey line) over eight time periods. During #1, Unit 4 accumulates (blue lines). During #2, Unit 4 rotates to dip steeply as it flows down the steep-gradient bedrock over the grounding zone, and Unit 2 (red lines) starts to accumulate at this steep angle. As the surface slope shallows through #3 and #4, Unit 2 becomes increasingly less steeply dipping as it accumulates. During #5 to #8, the ice shelf surface is approximately horizontal and accumulating layers of Unit 1 (grey lines) also remain approximately horizontal. Unit 3 in the JP-21 borehole would be located between Units 4 (blue) and 2 (red) but is not included here as it is not present at both sites.