Dynamics of dissolved neutral and acidic sugars in seawater

Carbohydrates are an important component of organic matter in the ocean. They originate from primary production, and are used by the phytoplankton cell as structural components and for energy storage, or released to the pool of dissolved organic matter by exudation, leakage, grazing or cell lysis. It is generally accepted that dissolved carbohydrates (dCHO) serve as an important food source for heterotrophic organisms, especially bacteria. More recently, it has been demonstrated that dCHO, and in particular acidic sugars, are also involved in abiotic processes, such as the formation of carbohydrate colloids and their subsequent aggregation into gel particles, or in the scavenging of trace metals, such as thorium, from the dissolved phase. The understanding of these processes is prerequisite to better estimate upper ocean particle dynamics and organic matter export to the deep-sea. To ascertain the temporal dynamics of dCHO and their partitioning into gel particles, we measured the abundances of neutral and acidic sugars and transparent exopolymer particles (TEP) during several lab, mesocosm and field studies. Analysis of neutral and acidic sugars in seawater was performed using High Performance Anion Exchange Chromatography (HPAEC) after desalination by dialysis (1000 Da) and acid hydrolysis. Here, we show preliminary results on the composition and abundance of dCHO and TEP in the course of phytoplankton blooms that were dominated by either diatoms or coccolithophores.