MSGSS
Parameterization of photoinhibition for phytoplankton
Phytoplankton—the microscopic plants of the ocean—drive roughly half of global primary production. To quantify how much carbon they fix, ocean scientists rely on photosynthesis–irradiance (P–I) curves, which describe how photosynthesis changes with light. Classical models capture the initial rise and saturation of these curves, but consistently fail under photoinhibition, the decline in photosynthesis caused by excessive light.
In this talk, I introduce a new and unusually simple P–I model that resolves this long-standing problem. Rather than using the traditional exponential decay with irradiance, we propose a saturating function of the reciprocal of irradiance. Tested against ~4,000 open-ocean P–I experiments, this formulation outperforms all existing models and avoids the interpretive pitfalls that have challenged the field for a century. It is mathematically more stable, statistically more accurate, and provides clean, direct estimates of key quantities (maximum photosynthesis rate, photoinhibition rate, and the onset of photoinhibition) directly from data, something that previous models could not reliably achieve.