Marginal sea Shelf-sea

Internal waves a b s t r a c t The hydrographic characteristics and the distributions of nitrateþnitrite, or (NþN), and soluble reactive phosphate, or SRP, in the Northern South China Sea Shelf-sea (NoSoCS) were determined in four transects across the shelf in the summer of 2010 and in two transects in the winter of 2011. The NoSoCS may be sub-divided into the inner shelf, the middle shelf and the outer shelf at water depths of o40 m, 40– 90 m and 90–120 m, respectively. The water in the inner shelf is colder and its concentrations in the nutrients and chlorophyll-a (Chl_a) are higher in both seasons while the water in the outer shelf is warmer and its concentrations are lower. With depth, since the mixed layer depth in the NoSoCS in the winter (70 m) and in the summer (40 m) are both shallower than the shelf break depth (120 m), the colder and relatively nutrient-rich upper thermocline-upper nutricline water in the open South China Sea (SCS) can freely extend into the NoSoCS to become its bottom water. This is a distinguishing characteristic of the NoSoCS as, unlike many of the more extensively studied temperate shelf-seas, vertical mixing within the NoSoCS, rather than shelf-edge processes such as upwelling, is the primary mechanism for bringing the nutrients from the sub-surface in the adjoining northern SCS to its mixe