Poster Session 3, Wednesday,  October  5, 16:00–18:00

Poster 3

Optical characterizations of photophysiology and nutrient limitation across the equatorial Pacific

Primary production plays a central role in the global carbon cycle and acts as a fundamental control in the cycling of biologically reactive elements in the ocean. As phytoplankton absorb light, the energy that is not used to drive photosynthesis can either be reemitted as fluorescence or dissipated as excess heat. Here, we take advantage of these competing processes to identify the inflection irradiance where chlorophyll fluorescence per unit chlorophyll decreases with increasing irradiance and excess absorbed energy is dissipated as heat. This fluorescence inflection irradiance has been found to be strongly related to the light saturation parameter for photosynthesis and can be used to characterize important photophysiological processes such as nonphotochemical quenching and phytoplankton photoacclimation. We use continuous underway sensors to resolve the surface light field, phytoplankton optical properties, and chlorophyll concentration and relate them to corresponding changes in biomass, community production, and nutrient concentration, specifically dissolved iron, across a 35 degree latitudinal gradient in the equatorial Pacific. We then explore the impacts of changes in phytoplankton community composition and nutrient limitation regimes on this optical photophysiological signal. The spatial patterns and relationships can be used to inform models of primary production and improve our understanding of drivers of ecological transitions across various biomes.

James Allen, University of Hawaii at Manoa, [email protected], 0000-0002-6765-7571

Fernanda Henderikx Freitas, University of Hawaii at Manoa, [email protected]

Angelicque White, University of Hawaii at Manoa, [email protected]

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