Using fluorescence to characterize dissolved organic matter in Antarctic sea ice brines

Sea ice plays a dynamic role in the air‐sea exchange of CO2. In addition to abiotic carbon fluxes, an active microbial community produces and remineralizes carbon, which can accumulate in sea ice brines as dissolved organic matter (DOM). In this study, the characteristics of DOM fluorescence in Antarctic sea ice brines the western Weddell Sea were investigated. Two humic‐like components were, which were identical to those previously found to accumulate in the deep ocean represent refractory material. Three amino‐acid‐like signals were found, one of which unique to the brines and another that was spectrally very similar to tryptophan and both in seawater and in brine samples. The tryptophan‐like fluorescence in the exhibited intensities higher than could be explained by conservative behavior during freezing of seawater. Its fluorescence was correlated with the accumulation of ‐rich DOM to concentrations up to 900 mmol L−1 as dissolved organic carbon (DOC) and, thus, potentially represented proteins released by ice organisms. A second, ‐poor DOM fraction also accumulated in the brines to concentrations up to 200 mmol L−1 but was not correlated with any of the fluorescence signals identified. of the high C: N ratio and lack of fluorescence, this material is thought to extracellular polymeric substances, which consist primarily of polysaccharides. clear grouping of the DOM pool into either proteinaceous or carbohydrate‐dominated indicates that the production and accumulation of these two subpools of DOM in ice brines is, to some extent, decoupled.