The present study is part of the INTERICE 4 project that ran at the Arctic Environmental Test basin (Hamburgische Schiffsbauversuchsanstalt) in October 2009. One aim of the experiment was to investigate the behaviour of dissolved organic matter (DOM) during sea-ice formation. DOM is important for biogeochemical cycles in oceans but also within sea ice, since it is produced and degraded by abiotic and biotic processes. The coloured fraction of DOM alters the optical properties of sea ice and therefore influences photosynthetic sympagic (ice-associated) organisms and photochemical processes. Fractionation during the formation of sea ice separates ice crystals from high saline brine, which also contains dissolved and particular matter. Diffusion and drainage cause the release of brine through the brine channel network into the under-ice water. However, we presumed that physical processes as well as biogeochemical interactions keep DOM within the ice causing an enrichment of organic matter relative to salt. Experiments were performed in 1 m³ bags filled with North Sea water (S = 33.1) from which half were treated with additional algae-derived DOM to investigate the impact of DOM concentration and quality on the fractionation. Within 1 week of freezing, under-ice water, bulk ice, brine and frost flowers were sampled and analysed. We addressed the characterization of DOM by a combination of methods: DOC and nutrient analysis, the absorption coefficient of CDOM, the spectral slope coefficient of CDOM, excitation emission matrices (EEMs) and PARAFAC modelling as well as size-exclusion chromatography (LC-SEC). The enrichment in ice and brine and frost flowers relative to salinity was calculated using the enrichment factor. Preliminary results based on CDOM absorbance, DOC/DON and nutrient analysis suggest an enrichment of DOM in ice and frost flowers, enrichment being higher at higher initial DOM concentrations. In brine, DOM is only enriched if the initial water was treated with additional DOM. Since this effect occurred after 1 day of ice growth, abiotic processes alone are assumed to prevent the rejection of DOM from ice in the same quantity as salts. Additionally, DOM, DOC/ DON and nutrients were found to be enriched in frost flowers, indicating upward movements of brine under very cold conditions.