To evaluate links between dissolved organic matter (DOM) dynamics and oxygen availability, we investigated the DOM composition at molecular level under varying levels of oxygen in a seasonally hypoxic fjord through a monthly time-series during February 2018 and November 2019. The DOM samples were collected from the near-bottom (60m, bottom depth: 71m) waters in the Compass Buoy Station, Bedford Basin, Nova Scotia, Canada. DOM was isolated by solid-phase extraction (SPE) and molecularly characterized using Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (FT-ICR-MS). Results from FT-ICR MS are reported as peak intensities of a nominal mass converted to a molecular formula.