Algal Bloom, Succession, and Drawdown of Silicate in the Chukchi Sea in Summer 2010

The Chukchi Sea is the inflow shelf between the Arctic and the Pacific. A comprehensive research on algal dynamics, physical–biological interactions, and impacts on nutrient drawdown was conducted in summer 2010. The study found a phytoplankton bloom with chlorophyll a (Chla) > 10 mg m−3 at ice edge in July. There were 36 shared algal species in both sea ice and open water, and those species dominated numerically both environments highlighting the seeding role of ice algae for the phytoplankton bloom. The succession pattern of diatom genera at three phases from sea-ice to open-water bloom and post-bloom conditions was revealed, and the phytoplankton abundance was positively correlated with the concentration of > 20 µm fractionated Chla. An anticyclonic eddy was detected in July and significantly reduced nutrient inventories in the impacted area relative to historical values. Phytoplankton composition was an important factor for both variable drawdown ratios of silicate to dissolved inorganic nitrogen (1.31–3.37) and dissolved inorganic nitrogen to dissolved inorganic phosphorus (7.62–12.32); however, both ratios also changed between July and August. The results indicated highly dynamic biogeochemical processes during the summer. In addition, the lower bound of silicate drawdown was comparable to the amount imported through the Bering Strait, indicating the Chukchi Sea is a significant silicate sink.