Temperature and iron (Fe) are key drivers of phytoplankton physiology, yet how they interact to influence phytoplankton growth and distribution remain poorly understood. In this study, we quantified the growth, photophysiology and cellular Fe content of Emiliania huxleyi across a range of temperature and iron concentrations. We further integrated these physiological responses with present-day and future projections of sea surface temperature and iron availability to predict shifts in the biogeographic distribution of E. huxleyi. Our results demonstrate that temperature and iron availability interactively influenced E. huxleyi growth. Iron limitation significantly reduced the maximum growth rate (μ_max), thermal niche width, and optimal growth temperature (T_opt). In addition, cellular Fe demand increased as temperatures deviated from Topt, revealing a U-shaped relationship between temperature and Fe demand. Under projected ocean warming and altered Fe supply, the distribution of E. huxleyi is expected to shift poleward. Notably, E. huxleyi is predicted to disappear from parts of tropical oceans under future climate scenarios. Our study reveals the critical role of temperature–iron interactions in coccolithophore physiology and distribution, highlighting the importance of nutrient limitation in modulating phytoplankton thermal responses and biogeographic patterns under climate change.
 

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