Contribution of small phytoplankton to total primary production in the Chukchi Sea

Given a projection of thriving small phytoplankton in the Arctic Ocean under climate-induced environmental changes, it is important to estimate the contribution of small phytoplankton (0.7–5 μm) to the total primary production in the Chukchi Sea, which is an important conduit of organic matter from the North Pacific to the Arctic Ocean. Based on a 13C–15N dual isotope tracer technique, small phytoplankton productivity measurements were taken during two consecutive cruises in the Chukchi Sea in 2004. The total phytoplankton carbon uptake rates ranged from 0 to 25.38 mg C m−3 h−1, whereas the uptake rates of small phytoplankton ranged from 0 to 2.87 mg C m−3 h−1. In comparison with the carbon uptake rates, total phytoplankton nitrate uptake rates ranged from 0 to 4.40 mg N m−3 h−1 while small phytoplankton nitrate uptake rates ranged from 0 to 0.39 mg N m−3 h−1. Ammonium uptake rates ranged from 0 to 8.34 mg N m−3 h−1 and from 0.01 to 2.18 mg N m−3 h−1, for total and small phytoplankton, respectively. Small phytoplankton contributed 24.80% (S.D.=±23.0%) to the total chlorophyll-a concentration, and 59.41% (S.D.=±52.12%) to the total carbon biomass due to its higher particulate organic carbon per chlorophyll-a unit during the two cruises in 2004. In the Chukchi Sea, the average contributions of small phytoplankton to carbon and total nitrogen (nitrate+ammonium) uptake rates were 31.72% (S.D.=±23.59%) and 37.31% (S.D.=±26.06%), respectively.