The lack of a marine DOM reference material is problematic and hinders method development and dataset alignment in marine biogeochemistry within the DOM characterisation field and in related subjects such as natural product discovery and trace metal speciation analysis. In order to fill this resource gap, we have prepared and characterised a marine DOM reference material from 45 m deep coastal seawater obtained from the Tjärnö Marine Laboratory (Gothenburg University) on the west coast of Sweden. The material was collected in this first effort in May 2022 from 1,500 L seawater using a commercially available aqueous-compatible C18 column (C18-AQ hereafter), and after sample clean-up, totalled 1.06 g in mass. We have given the sample a unique designation 'Tjarno Reference Material -May 2022' (TRM-0522), allowing for future efforts to collect and distribute more material. In this article, we characterise the material using HRMS, UPLC-HRMS/MS and NMR.