Nutrient dynamics and coupling with phytoplankton species composition during the spring blooms in the Yellow Sea

Nutrient dynamics during spring phytoplankton bloom period in the Yellow Sea (YS) was discussed based on field observations performed in February, March–April and June 2009. Abundant nutrients and optimal molar ratios among dissolved inorganic nitrogen, phosphorus and Silicic acid in early spring provided favorable conditions for blooming phytoplankton. Depletion of phosphorus and nitrogen in the euphotic zone terminated the spring bloom in the central YS in early summer. Continuous observations in every 3 h for about 4–5 days were conducted to investigate supply, consumption and other characteristics of nutrients during phytoplankton bloom period at two drift stations. The major sources of nutrients are Yellow Sea Warm Current water (in winter and early spring) and Changjiang Diluted Water (in early summer). The upward nutrient fluxes from deep water to the euphotic zone (upper 30 m depth) by means of diffusion and turbulent entrainment were important nutrient sources to sustain the bloom, and they appeared to account 56% of N, 56% of P and 69% of Si for phytoplankton growth demand. 57–76% of DIN and 46–68% of PO43− in the upper 10–20 m water were utilized by phytoplankton in about one week to produce a bloom.