This 2D cross-section renders the same water-column physics as the 3D version, viewed edge-on instead of in perspective. Sunlight is cut down by two stacked absorbers, snow and ice, following Beer–Lambert extinction:
I_under = I0(sun) · e^(−k_snow·d_snow) · e^(−k_ice·d_ice)
k_snow ≈ 15 m⁻¹ (snow is a far stronger absorber than ice)
k_ice ≈ 1.5 m⁻¹
Ice-algae growth is light-limited but photoinhibited at high irradiance (Steele's curve), then grazed by copepods and lost to sinking/mortality:
μ(I) = μmax · (I/Iopt) · e^(1 − I/Iopt)
dB/dt = μ(I)·B − g·Z·B/(B+Kb) − m·B
dZ/dt = a·g·Z·B/(B+Kb) − r·Z
Difference from the 3D version: the copepod seed population here starts at a realistic low pre-bloom density (≈1.2 proxy units) rather than a high one. With the 3D model's original seed of 6 units, grazing pressure at the default sliders overwhelms the tiny 0.15 mg/m³ starter biomass within well under a simulated day — the bloom never gets a chance to establish at any but the brightest settings. Lowering the starter grazer stock lets the light-driven bloom actually appear before consumers build up on it, matching the real Arctic succession (grazers increase after the bloom starts, not before). The light physics and growth/grazing equations themselves are unchanged.
- Snow depth — the single biggest lever on under-ice light; a thin snow cover can trigger an under-ice bloom weeks before open water.
- Ice thickness — thinning multi-year ice transmits more PAR even with the same snow load, a key climate-driven shift.
- Sun elevation — stands in for the spring progression from polar night toward the equinox, raising I0.
- Grazing pressure — copepods (Calanus) graze the algae layer and store its lipids as wax esters, the energy currency that arctic cod, seals and eventually polar bears depend on.
The right-hand strip chart plots under-ice PAR, algae biomass and copepod population against simulated days, so you can watch the bloom rise and fall in real time rather than only reading a snapshot number.