Spatiotemporal variation characteristics and related affecting factors of dissolved carbohydrates in the East China Sea

- Concentrations of MCHOs and PCHOs exhibited an evident spatiotemporal variation.
- Phytoplankton biomass controlled seasonal and diel variation of carbohydrates.
- Carbohydrates have similar source and transformation mechanism to DOC.
- Salinity correlated negatively with MCHOs, TCHOs, DIN and chlorophyll a.
- Carbohydrate enrichment was sometimes found in near-bottom water.

Carbohydrates are the largest identified fraction of dissolved organic carbon and play an important role in biogeochemical cycling in the ocean. Seawater samples were collected from the East China Sea (ECS) during June and October 2012 to study the spatiotemporal distributions of total dissolved carbohydrates (TCHOs) constituents, including dissolved monosaccharides (MCHOs) and polysaccharides (PCHOs). The concentrations of TCHOs, MCHOs and PCHOs showed significant differences between summer and autumn 2012, and exhibited an evident diurnal variation, with high values occurring in the daytime. Phytoplankton biomass was identified as the primary factor responsible for seasonal and diurnal variations of dissolved carbohydrates in the ECS. The TCHOs, MCHOs and PCHOs distributions in the study area displayed similar distribution patterns, with high concentrations appearing in the coastal water. The influences of chlorophyll-a, salinity and nutrients on the distributions of these carbohydrates were examined. A carbohydrate enrichment in the near-bottom water was found at some stations, implying that there might be an important source of carbohydrate in the deep water or bottom sediment.