Seawater samples were collected at various depths during the MOSAiC (Multidisciplinary drifting Observatory for the Study of Arctic Climate) expedition. The following carbohydrate fractions were analyzed: dissolved free carbohydrates (DFCHO), dissolved combined carbohydrates (DCCHO), and particulate combined carbohydrates (PCCHO). DFCHO and DCCHO concentrations were determined from 0.2 µm filtered seawater. Samples were first desalinated by electrodialysis and subsequently analyzed using high-performance anion exchange chromatography with pulsed amperometric detection (HPAEC-PAD). PCCHO concentrations were measured from material retained on 0.2 µm polycarbonate membrane filters. DCCHO and PCCHO were released by acid hydrolysis. All carbohydrate fractions (DFCHO, DCCHO, PCCHO) were quantified as the sum of their constituent monosaccharides, including arabinose, glucose, galactose, glucosamine, galactosamine, muramic acid, galacturonic acid, and others. Carbohydrate measurements were obtained from samples of MOSAiC legs 1, 3, 4, and 5.

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