Unraveling Both Community Divergences and Driving Factors of Pelagic Microbial Food Web in Different Water Masses of the Eastern Arctic Ocean

Abstract Microbial food webs (MFWs) constitute the foundational framework of marine pelagic ecosystems, yet their community structure, trophic interactions, and associated abiotic driving factors remain inadequately characterized in the Arctic Ocean. To fill this gap, we conducted a comprehensive ship‐based survey during summer 2020 to investigate three MFW trophic levels (picoplankton—Pico, nanoplankton—Nano, microzooplankton—Micro) from surface to 500 m layers. Each MFW component displayed a consistent subsurface peak in its vertical distribution. Additionally, five distinct water masses were identified, and each harboring a distinctive MFW composition. Within this framework, heterotrophic prokaryotes dominated numerically across all water masses, and Pacific‐origin Synechococcus emerged as a valuable bioindicator for tracking Arctic environmental fluctuations. Notably, trophic‐level abundance ratios conformed to a pyramidal structure, spanning five and two orders of magnitude for Pico:Micro (3.5–12.8 × 10 5 :1) and Nano:Micro (1.6–10.0 × 10 2 :1), respectively. Unlike biomass ratios, for which spanned one and zero order in Pico:Micro (0.4–1.2 × 10 1 :1) and Nano:Micro (0.8–2.6:1), respectively. Concerning biotic‐abiotic interactions, both abundance and biomass of each MFW component demonstrated a linear increase with both temperature and Chl a concentrations in Pacific Summer Water. Therein, picoeukaryotes exhibited the steepest slope revealed that their heightened sensitivity to temperature changes. Furthermore, the driving factors for MFW trophic linkages varied significantly among water masses, and the bottom‒up control (resource availability) predominating microzooplankton composition. This study upon trophic‐level interaction establishes a baseline for quantifying and predicting how future environmental changes may affect pelagic MFWs in polar marine ecosystems.