The unique chromatographic behaviour of DOM was investigated on three exemplary water samples representing coastal DOM, oceanic surface DOM and oceanic refractory DOM. Weddell Sea surface (30 m depth, oceanic surface DOM) and deep water (1356 m depth, refractory DOM) was sampled with a rosette sampler on RV Polarstern during ANT XXII/2 (station PS67/006-130, latitude -67.5633, longitude -55.3448) and are described elsewhere (El Naggar et al., 2007; Koch et al., 2008). Coastal DOM is routinely extracted from southern North Sea (latitude 54.1447, longitude 7.8711) and used as an in-house laboratory standard. Mass spectra were obtained with liquid chromatography coupled to a Fourier-transform Orbitrap mass spectrometer (LC-FT-Orbitrap-MS) with negative electrospray ionisation. A Q-Exactive Plus (Thermo Fisher Scientific, Bremen, Germany) was coupled to an ultra-performance liquid chromatography system (UPLC, Vanquish, Thermo Fisher Scientific, Bremen, Germany). Reversed phase chromatography was done with a C18 column (Waters AQUITY 2 x 100 mm, 1.7 µm) column at 0.3 mL min 1 and a linear gradient: A (ultrapure water, 4 mmol L 1 ammonium formate) 2 min: 99 %, 11 min: 0 %, 14.9 min: 99 %; B (MeOH, 4 mmol L 1 ammonium formate) 2 min: 1 %, 11 min: 100 %, 14.5 min 100 %, 14.9 min 1 %. The exact mass lists and intensities of the 1.1 min binned scans were exported with the Xcalibur software package (Thermo Electron Corporation).