On the Variability of Phytoplankton Photophysiology Along a Latitudinal Transect in the North Atlantic Surface Ocean

• Main Authors: Aardema, Hedy M., Slagter, Hans A., Hrabe de Angelis, Isabella, Calleja, Maria Ll., Dragoneas, Antonis, Moretti, Simone, Schuback, Nina, Heins, Lena, Walter, David, Weis, Ulrike, Haug, Gerald H., Schiebel, Ralf
• Format: Article in Journal/Newspaper
• Language: English
• Published: American Geophysical Union 2024
• Subjects: phytoplankton; photophysiology; North Atlantic; variable fluorescence; surface ocean; photosynthesis; North East Atlantic; Subarctic
• Online Access: https://hdl.handle.net/20.500.11850/692916; https://doi.org/10.3929/ethz-b-000692916

Phytoplankton photosynthesis is the first step of energy capture in the open ocean and is therefore fundamental for global biogeochemical processes and ecosystem functioning. High-resolution methods are required to fully capture the variability of marine photosynthesis and its environmental drivers. Here, we combine two high-resolution underway methods to study phytoplankton photophysiology, Fast Repetition Rate fluorometry and Flow Cytometry, along a transect in the North-East Atlantic Ocean from the polar circle to the equator. Significant spatial distinctions in photophysiological strategies were found between biogeographical provinces. The most pronounced distinction was present between the subarctic North Atlantic and the oligotrophic subtropical gyre, where the latter was typified by high photosystem II (PSII) turnover rates, low pigment-to-cell volume ratios, low PSII quantum efficiency and low absorption cross sections for photochemistry in PSII. Small-scale variability along the transect results from varying diel cycles in photophysiology, possibly governed by light availability and cell metabolism. In general, we found that variability in PSII photochemistry was associated with variability in sea surface temperature, whereas the median mixed layer irradiance could explain more of the variation in the light harvesting capacity of the phytoplankton community. This implies that the expected climate change driven shoaling of the mixed layer may impact phytoplankton light harvesting strategies. Marine photosynthesis is the basis of life in the ocean and therefore plays a fundamental role in the worlds' largest ecosystem. Phytoplankton adjust their photosynthesis to different environmental conditions, such as nutrients and light. Here, we combine data from two high-resolution methods to study phytoplankton in the eastern North Atlantic Ocean from the polar circle to the equator. We show that the photosynthesis of phytoplankton differs between oceanographic regions and that daily cycles as well as ...