[1] Two cruises were carried out in the summer and winter of 1998 to study coupled physical-chemical-biological processes in the South China Sea and their effects on phytoplankton stock and production. The results clearly show that the seasonal distributions of phytoplankton were closely related to the coupled processes driven by the East Asian Monsoon. Summer southwesterly monsoon induced upwelling along the China and Vietnam coasts. Several mesoscale cyclonic cold eddies and anticyclonic warm pools were identified in both seasons. In the summer, the upwelling and cold eddies, both associated with rich nutrients, low dissolved oxygen (DO), high chlorophyll a (Chl a) and primary production (PP), were found in the areas off the coast of central Vietnam, southeast of Hainan Island and north of the Sunda shelf, whereas in the winter they form a cold trough over the deep basin aligning from southwest to northeast. The warm pools with poor nutrients, high DO, low Chl a, and PP were found in the areas southeast of Vietnam, east of Hainan, and west of Luzon during the summer, and a northwestward warm jet from the Sulu Sea with properties similar to the warm pools was encountered during the winter. The phytoplankton stock and primary production were lower in summer due to nutrient depletion near the surface, particularly PO 4 . This phosphorus depletion resulted in phytoplankton species succession from diatoms to dinoflagellates and cyanophytes. A strong subsurface Chl a maximum, dominated by photosynthetic picoplankton, was found to contribute significantly to phytoplankton stocks and production.

Micro-and nanogels prepared by ionically crosslinking chitosan with tripolyphosphate (TPP) attract keen interest as potential drug carriers. To achieve their optimal performance, it is essential to control their stability to aggregation and dissolution. Yet, literature on this subject (especially at physiological ionic strength and pH) remains filled with opposing reports. Recently, one of us hypothesized that these conflicting findings might stem from: (1) variations in the chitosan molecular structure;(2) the dissimilar particle concentrations used by the various groups; and (3) occasional overreliance on dynamic light scattering (DLS) as the sole analytical tool. To explore this hypothesis, here we use isothermal titration calorimetry, light scattering and UV-Vis spectroscopy to analyze the effects of chitosan degree of deacetylation (DD) and particle concentration on chitosan/TPP particle stability. Their dissolution stability increases with the chitosan DD (due to the stronger chitosan/TPP binding) and when the particles are used at higher concentrations, and evidently depends on the chitosan molecular weight.Conversely, their aggregation stability decreases with the DD, because the chitosan is more prone to TPP bridging and becomes more lyophobic at near-neutral (physiological) pH. We also show how using DLS-derived size distributions as the sole tool for characterizing particle stability can lead to erroneous conclusions. Comparison of these findings to literature experimental conditions reconciles many of the opposing reports and provides essential guidelines for tuning chitosan/TPP particle stability.

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The East China Sea (ECS) and the Southern Yellow Sea (SYS) ecosystem is undergoing dramatic changes, but the spatiotemporal patterns and forcing mechanisms of phytoplankton variations remain understudied. Phytoplankton lipid biomarkers are useful proxies for productivity and community structure changes, and they were measured in suspended particles of more than 81 sites from spring and summer of 2011 in the ECS and SYS. In spring, the concentrations of brassicasterol (4.7-127 ng L À1 ) and dinosterol (0.7-37 ng L À1 ) were markedly higher in the northern and central SYS, while C 37 alkenones (0-15 ng L À1 ) were detected at only seven sites in the ECS. In summer, brassicasterol (25.3-1178 ng L À1 ) and dinosterol (0-125 ng L À1 ) showed high values off the Changjiang River Estuary (CRE), while C 37 alkenones (0-410 ng L À1 ) had high values in the northwest and central SYS. The mean concentrations of the three lipid biomarkers in summer were 3 to 61 times higher than those in spring. Spatiotemporal patterns of biomarkers reveal higher ratios of diatom/dinoflagellate and diatom/haptophyte in higher productivity areas, off the CRE in summer and the northern and central SYS in spring. This study validates the applicability of brassicasterol, dinosterol, and alkenones as proxies of productivity and community structure of the three phytoplankton taxa: diatoms, dinoflagellates, and haptophytes. The results indicate that nutrients (in summer) and turbidity-induced photosynthetic available radiation (in spring) play important roles in regulating spatiotemporal variations of phytoplankton in the ECS and SYS.