Variations in dissolved free and combined carbohydrates during a phytoplankton bloom in the northern North Sea were investigated. Large amounts of carbohydrates are released into seawater during the bloom; the major portion of this release occurs towards the end of the bloom. A considerable part of the released carbohydrates is in the combined form. Free dissolved carbohydrates are formed mainly by in situ hydrolysis of dissolved combined carbohydrates. Glucose and fructose dominate the free dissolved carbohydrate fraction. Glucose is formed biologically, and fructose biologically and abiotically from glucose. Glucose comprises more than 60 % of the combined carbohydrate fraction, followed by mannose, galactose and xylose. The production and release of dissolved carbohydrates in large amounts appear to be related to the availability of nutrients. The vertical distribution of dissolved carbohydrates is controlled by boundary layers in mid-water.
Monosaccharide composition of acid‐hydrolyzable carbohydrates was analyzed in particulate matter collected during a plankton bloom in the northern North Sea. Concentrations of total particulate carbohydrates varied from 50 nmol·liter−1 to >600, with maximum concentrations in the upper layers above 1% light depth. The monosaccharide spectra, considered in conjunction with those of dissolved carbohydrates from the same samples, suggest that the variations observed were caused by variations in the production of carbohydrates by phytoplankton and significant loss of produced carbohydrates into the dissolved fraction. Two loss phases could be discerned: first, labile glucose polymers, followed by the relatively stable structural polysaccharides.
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