Dissolved organic matter (DOM) plays a pivotal role in the Arctic Ocean's biogeochemical cycles, yet its size-resolved molecular composition remains complex and variable under changing climate conditions. In this study, we investigated the size spectra and chemical composition of DOM in the Arctic Ocean using Asymmetrical Flow Field-Flow Fractionation (AF4) and high-resolution Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (FT-ICR-MS). We present a comprehensive dataset derived from samples collected during Arctic expeditions in 2014, 2023, and 2024. This multi-year investigation allows for the assessment of both spatial heterogeneity and inter-annual variability. Specifically, we report detailed molecular characteristics for DOM in the Chukchi Sea, highlighting distinct DOM sources and degradation states across different size fractions. Furthermore, we present new findings from 2023 and 2024, revealing unique molecular signatures that suggest that diel migration of zooplankton might be the additional source for the deep DOM. By integrating size fractionation with ultra-high-resolution mass spectrometry, our results provide new insights into the cycling mechanisms of Arctic DOM and its response to environmental changes.
 

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