| Summary: | First posted online: Fri, 31 Jul 2020 09:53:38 | This content has not been peer reviewed. Manuscript submitted to JGR: Oceans The article of record as published may be found at https://doi.org/10.1002/essoar.10503749.1 In July 2011, observations of a massive phytoplankton bloom in the ice-covered waters of the western Chukchi Sea raised questions about the extent and frequency of under seaice blooms and their contribution to the carbon budget in the Arctic Ocean. To address some of these questions, we use the fully-coupled, high-resolution Regional Arctic System Model to simulate Arctic marine biogeochemistry over a thirty-year period. Our results demonstrate the presence of massive under sea-ice blooms in the western Arctic not only in summer of 2011 but annually throughout the simulation period. In addition, similar blooms, yet of lower magnitude occur annually in the eastern Arctic. We investigate the constraints of nitrate concentration and photosynthetically available radiation (PAR) on the initiation, evolution and cessation of under sea-ice blooms. Our results show that increasing PAR reaching the ocean surface through the sea-ice in early summer, when the majority of ice-covered Arctic waters have sufficient surface nitrate levels, is critical to bloom initiation. However, the duration and cessation of under sea-ice blooms is controlled by available nutrient concentrations as well as by the presence of sea-ice. Since modeled critical PAR level are consistently exceeded in summer only in the western Arctic, we therefore conclude that the eastern Arctic blooms shown in our simulations did not develop under sea ice, but were instead, at least in part, formed in open waters upstream and subsequently advected by ocean currents beneath the sea ice. This research was partially supported by the following: Collaborative Research: Understanding Arctic Marine Biogeochemical Response to Climate Change for Seasonal to Decadal Prediction Using Regional and Global Climate Models, Award number IAA1417888, ...
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