Nitrogen Limitation of the Summer Phytoplankton and Heterotrophic Prokaryote Communities in the Chukchi Sea

• Published in: Frontiers in Marine Science
• Main Authors: Mills, Matthew, Brown, Zachary, Laney, Samuel, Ortega-Retuerta, Eva, Lowry, Kate, van Dijken, Gert, Arrigo, Kevin
• Other Authors: Department of Earth System Science Stanford (ESS), Stanford EARTH, Stanford University-Stanford University, Woods Hole Oceanographic Institution (WHOI), Laboratoire d'Océanographie Microbienne (LOMIC), Institut national des sciences de l'Univers (INSU - CNRS)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Observatoire océanologique de Banyuls (OOB), Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2018
• Subjects: phytoplankton; nitrogen; Chukchi Sea; nitrate; nutrient limitation; [SDE]Environmental Sciences; [SDU.STU.OC]Sciences of the Universe [physics]/Earth Sciences/Oceanography; [SDV.MP]Life Sciences [q-bio]/Microbiology and Parasitology; Arctic; Chukchi; Phytoplankton
• Online Access: https://hal.science/hal-04002590; https://hal.science/hal-04002590/document; https://hal.science/hal-04002590/file/fmars-05-00362.pdf; https://doi.org/10.3389/fmars.2018.00362

Major changes to Arctic marine ecosystems have resulted in longer growing seasons with increased phytoplankton production over larger areas. In the Chukchi Sea, the high productivity fuels intense benthic denitrification creating a nitrogen (N) deficit that is transported through the Arctic to the Atlantic Ocean, where it likely fuels N fixation. Given the rapid pace of environmental change and the potentially globally significant N deficit, we conducted experiments aimed at understanding phytoplankton and microbial N utilization in the Chukchi Sea. Ship-board experiments tested the effect of nitrate (NO 3 −) additions on both phytoplankton and heterotrophic prokaryote abundance, community composition, photophysiology, carbon fixation and NO 3 − uptake rates. Results support the critical role of NO 3 − in limiting summer phytoplankton communities to small cells with low production rates. NO 3 − additions increased particulate concentrations, abundance of large diatoms, and rates of carbon fixation and NO 3 − uptake by cells >1 µm. Increases in the quantum yield and electron turnover rate of photosystem II in +NO 3 − treatments suggested that phytoplankton in the ambient dissolved N environment were N starved and unable to build new, or repair damaged, reaction centers. While some increases in heterotrophic prokaryote abundance and production were noted with NO 3 − amendments, phytoplankton competition or grazers likely dampened these responses. Trends toward a warmer more stratified Chukchi Sea will likely enhance summer oligotrophic conditions and further N starve Chukchi Sea phytoplankton communities.