9All life exchanges molecules with its environment. While these metabolites are commonly 10 measured in terrestrial and limnic ecosystems, the presence of salt in marine habitats has 11 hampered quantitative analyses of the ocean metabolome. To overcome these limitations, we 12 developed SeaMet, a gas chromatography-mass spectrometry (GC-MS) method that detects 13 hundreds of metabolites down to nano-molar concentrations in less than one milliliter of 14 seawater. Using a set of metabolites dissolved in artificial seawater to benchmark our method, 15 we show metabolite signal detection increased on average across ions by 324 fold in comparison 16 to standard GC-MS methods. Our observed signal improvement occurred across tested 17 metabolite classes and provides reproducible and quantifiable results. To showcase the 18 capabilities of our method, we used SeaMet to explore the production and consumption of 19 metabolites during culture of a heterotrophic bacteria that is widespread in the North Sea. Our