This is a plan-view (map) grid of the same marine-ice-sheet physics as the 3D flowline model, seen from above instead of from the side. Each grid cell holds an ice thickness H(x,y); whether it is grounded or floating is set purely by the local depth of bedrock (which only varies along the flow direction x) against Archimedes' flotation criterion:
H_f(x) = (ρ_w / ρ_i) · (sea level − bed(x))
grounded if H(x,y) ≥ H_f(x), floating otherwise
Mass conservation and Glen's-law diffusive flux (n≈3) are solved independently along every row y: ∂H/∂t = a − ∂Q/∂x, Q ∝ H^(n+2)|∂S/∂x|^(n−1)∂S/∂x, with a Schoof-style grounding-line export flux Q_gl ∝ H_gl^α (α≈4.2) that makes retreat self-accelerating on a retrograde bed — the MISI mechanism. What makes this a genuinely 2D field rather than one line copied sideways is a lateral drag profile: flow is fastest in a central channel and drags against slower margins (as real Antarctic ice streams do against their shear margins), plus a small lateral diffusive coupling between neighbouring rows. That channelization means the grounding line and calving front are not straight — they bow forward in the fast core and lag at the margins, producing a curved, embayment-like front and icebergs calving independently at different points across the width, all from per-row application of the identical 1D equations used in the 3D version.
- Bed profile — retrograde (deepens inland, unstable) vs prograde (shallows inland, stable); read directly off the grid as the grounded region growing or shrinking without bound.
- Basal slipperiness / ice softness — scales flux and grounding-line export in every row.
- Sub-shelf ocean melt — thins the floating shelf uniformly; strong enough melt can trigger runaway retreat even on a stable bed profile.
- Sea-level offset — raises the flotation threshold everywhere, an independent MISI trigger.