UV-B, the Ozone Hole & Phytoplankton

Atmosphere

Ozone column 300 DU

Solar zenith angle 20°

Ocean

Water clarity K_d 0.12 m⁻¹

Live Readouts

Surface UV Index

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DNA-damage index

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Mean phytoplankton productivity (0–30 m)

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How it works

Stratospheric ozone absorbs solar UV-B (280–315 nm). Thinning it — the Antarctic "ozone hole" that forms each austral spring, ~150–220 Dobson Units versus a ~300 DU global baseline — lets more UV-B reach the surface. The relationship is captured by the Radiation Amplification Factor (RAF):

%ΔUV ≈ -RAF × %ΔO3
RAF ≈ 1.1  (erythemal / UV Index)
RAF ≈ 2.3  (DNA-damaging action spectrum, McKenzie et al. 2011)

Surface UV also falls off with solar zenith angle θ as the slant path through the atmosphere lengthens:

UVI(θ, DU) = UVI_ref · (DU_ref/DU)^RAF · (cosθ)^b,   b ≈ 0.65
DNA(θ, DU) = DNA_ref · (DU_ref/DU)^RAF_DNA · (cosθ)^b

Under water, UV-B is absorbed exponentially with depth z (Beer–Lambert law), governed by the diffuse attenuation coefficient K_d (clear open ocean ≈ 0.05–0.15 m⁻¹, turbid coastal water > 0.3 m⁻¹):

I(z) = I(0) · e^(−Kd·z)

Phytoplankton primary production is photoinhibited by excess UV via a saturating Kirk-type response — DNA damage and photosystem-II repair are overwhelmed at high dose:

P(z)/Pmax = 1 / (1 + (I(z)/Ih)^n)

Field measurements in the Bellingshausen Sea under the Antarctic ozone hole (Smith et al., Science 1992) found measurable reductions in primary production in the UV-exposed mixed layer — the mechanism this simulator reproduces: thinner ozone → higher surface UV Index and DNA-damage index → lower productivity near the surface, recovering with depth as the water column attenuates the dose. Toggle the two presets to compare a healthy ozone layer against a spring ozone-hole event at the same water clarity.

Healthy phytoplankton UV-photoinhibited

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