National Research Institute of Fisheries Science, Fisheries Research Agency
Abstract
Size-fractionated primary productivity and chlorophyll a (Chl a) concentration were measured in the middle domain of the southeastern Bering Sea shelf in summer 2004. A subsurface Chl a maximum of 7.9 μg l^(-1) was observed at 20 m depth, around the pycnocline in the coastal front around St. Paul Island. Large phytoplankton exceeding 10 μm in size accounted for about 80% of the primary productivity and Chl a concentration at the subsurface Chl a maximum. The growth rate of the large phytoplankton was estimated to be 0.09 d^(-1), which is low compared to previously reported growth rates as well as other rates obtained in this study (0.06-0.56 d^(-1)). More abundant nutrient supply from deeper to upper layers due to the topography of the area is considered the leading factor producing the subsurface Chl a maximum. Moreover, ineffective grazing of the large phytoplankton in the middle shelf domain and their accumulation around the pycnocline are thought to be advantageous factors maintaining the subsurface Chl a maximum
