We applied ultrahigh-resolution mass spectrometry to monitor the production and turnover of 7,360 distinct molecular DOM features in an unprecedented long-term mesocosm study in a Swedish Fjord, covering a full cycle of marine production. DOM concentration and molecular composition did not differ significantly between present-day and year 2100 CO2 levels.Measurements of DOC and TDN: High-Temperature Catalytic Oxidation on Shimadzu TOC-VCPH analyzer with ASI-V auto sampler; values represent mean of two replicates; presumable outliers were excluded from the dataset (values 30 % higher than mean of the two replicates)"