Study On The Size Fractionated Chlorophyll A And Primary Productivty In Spring And Summer In The Yellow Sea And East China Sea

Chlorophyll a is the main pigment in phytoplankton that carries out the process ofphotosynthesis and a good indicator of algal biomass in the ocean. Primaryproductivity indicates the capacity of producing organic compounds by phytoplankton.It plays an important role in the global carbon cycle, leading to a strong influence onglobal climate change.Based on the two cruises of―973‖porject―The key processes, mechanism andecological consequences of jellyfish bloom in China coastal waters‖, the size fractionatedchlorophyll a and primary productivity were studied in the Yellow Sea and East ChinaSea during the spring and summer of2011. The average chlorophyll a content inwater column in spring was1.426mg/m~3, whereas the value in summer (0.64) mg/m~3showed a significant decrease. The chlorophyll a concentration from the surface to thebottom uniformly distributed in spring, and the vertical distribution of chlorophyll aconcentration showed a more obvious stratification in summer in the South YellowSea. The highest value of chlorophyll a was in the upper waters of0-20m in springand summer in the East China Sea, and the high value areas were concentrated in thewest of124.5°N waters.The chlorophyll a concentration and phosphate concentration showed significantlynegative correlations, and showed significant positive correlations with the nitrogen tophosphorus ratio in the whole investigation sea area in spring, therefore the phosphatemay become the controlling factor for phytoplankton growth in spring.In the spring, the range of Micro-, Nano-and Pico-phytoplankton concentrationwas0~4.36,0.02~2.27,0~2.66mg/m~3, and the average concentrations were0.56,0.31and0.14mg/m~3, with their contribution of55.4%、30.8%and13.8%to the totalchlorophyll a concentration respectively. In the summer, the range of Micro-, Nano-and Pico-phytoplankton concentration was0~6.78,0~2.59,0~0.86mg/m~3, and theaverage concentrations were0.50、0.24and0.07mg/m~3, with their contribution of61.8%,30.1%and8.1%to the total chlorophyll a concentration respectively. The vertical distribution of micro-phytoplankton was homogeneous, whereas theconcentration of Nano-and Pico-phytoplankton decreased with the depth in the spring.In summer, there was abrupt change on the depth of10m. The concentration ofmicro-and Nano-phytoplankton was much higher on the layer shallower than10m.The concentration of Pico-phytoplankton was low at all layers in summer. The changeon the pattern of temperature, salinity and nutrients was the major factors resulting inthe change of the phytoplankton size structure in the Yellow Sea and East China Sea.The average primary productivity in water column was993.9mgC/(m~2·d) inspring, and1274mgC/(m~2·d) in summer，which increased by comparing with that of1984-1985. The horizontal distribution of primary productivity shows less variation insummer than in spring. It was the highest in the middle of the Yellow sea and theChangjiang Estuary in spring, and the highest in the coast of Shandong, the coast ofZhejiang and the Changjiang Estuary in summer. The contribution of Micro-, Nano-and Pico-phytoplankton to the total primary productivity were24.08%,72.65%,3.27%in the spring and7.96%,88.38%,3.66%in summer.The spatial of pattern of the chlorophyll a concentration are similar with the past20years in different periods. The chlorophyll a concentration significantly increasedin the Yellow Sea and East China Sea, especially in the East China Sea. The primaryproductivity showed an increasing trend, but fluctuated significantly.