Distribution Characteristics Of Dissolved Carbohydrates In The Yellow Sea And The East China Sea

Carbohydrates are ubiquitous in marine environments, including marine organisms, dissolved organic matter, colloids, sediments, and sinking and suspended particles. They are the prime products of photosynthesis which can be transformed into other essential components such as proteins, lipids and nucleic acids, they also are the largest identified fraction of dissolved organic carbon in the ocean. Therefore, they play important roles in the marine food web cycle and marine carbon cycle.In this present dissertation, we systematically studied distributions, influencing factors of dissolved monosaccharides (MCHO) and polysaccharides (PCHO), and their contributions to dissolved organic carbon (DOC) in the continental shelf of China—the Yellow Sea and the East China Sea. Furthermore, we focus on the production of MCHO and PCHO during the growth stages of two typical offshore algae by laboratory culture experiment. The main conclusions are drawn as follows:1. Seawater samples were collected from the Yellow Sea (YS),the Changjing River estuares and its adjacent area for determinations of dissolved monosaccharide (MCHO), polysaccharide (PCHO) from November to December in 2009. Their horizontal and vertical distributions were systematically studied in this paper. In the surface water, the concentrations of MCHO and PCHO ranged from 0.1 to 52.4μmol C/L and from 0.1 to 214.7μmol C/L, with average values of 11.0±9.9 and 39.8±49.9μmol C/L respectively. Both MCHO and PCHO have similar distribution patterns, with several closed high or low value areas accounting for different reasons. No strong correlations were observed between carbohydrate species (MCHO and PCHO) and phytoplankton, suggesting that it was not the sole factors controlling the concentration of carbohydrate in the surface water and water columns. In late autumn, there were not obvious change patterns of MCHO and PCHO concentrations within the water column due to strong vertical mixing at our studied transects. And several carbohydrate enrichments in the near-bottom waters were found at the bottom of several stations in our studied water column, which underlines that there are important sources of carbohydrate in deep waters or bottom sediments.2. Seawater samples were collected at 35 stations, including 6 stations in the vertical section, in the East China Sea from December 2009 to January 2010. Concentrations of monosaccharides (MCHO), polysaccharides (PCHO), total dissolved carbohydrate (TCHO) were measured with TPTZ method, and their horizontal and PN vertical distributions were studied. The results showed that the horizontal distributions of MCHO, PCHO and TCHO were obviously influenced by the Yangtze River effluent and the oligotrophic Kuroshio waters, displaying a decreasing trend from the inshore to the offshore. At transect PN, because of strong vertical mixing of seawater caused by strong northeast monsoon in winter, no obvious change pattern was observed in the profiles of concentrations of MCHO, PCHO and TCHO. Linear regressive analyses were made between the concentrations of TCHO and environmental parameters measured at three transects outside the Yangtze River estuary, and the results indicated that the concentrations of TCHO was negatively correlated with salinity and temperature, while it was positively correlated with chlorophyll a.3. The production of MCHO and PCHO are studied in different growth stages of Phaeodactylum tricornutum and Chlorella vulgaris. Moreover, we have studied the basic physiology of MCHO and PCHO in axenic cultures, and MCHO and PCHO contents of these two algae have been found to be important controls on MCHO and PCHO dynamics in the seawater. The results are shown as follows:To varing degrees, the two algae release a certain amout of MCHO and PCHO. The content of MCHO of Chlorella vulgaris is higher than Phaeodactylum tricornutum; the content of PCHO of Phaeodactylum tricornutum is higher than Chlorella vulgaris. On the whole, the MCHO and PCHO concentrations per Chl-a of Chlorella vulgaris are 19 and 1.7 times higher than Phaeodactylum tricornutum, respectively. And MCHO and PCHO have low concentrations in the exponential phase and stationary phase; in the senescent stage, the algae cells produce the largest amount of TCHO. In addition, the concentrations of MCHO and PCHO are significant positively correlated with DOC, respectively, while they are not correlated with Chl-a.