New production in polar regions: the role of environmental controls

Abstract

Polar regions have extreme environmental conditions, but the degree to which polar phytoplankton have adaptations, particularly with respect to nitrogen uptake, is unknown. The effects of temperature, nutrient concentrations and irradiance on nitrogen uptake were investigated in diverse (Arctic and Antarctic) polar environments by analysing experimental data as well as previously published results. The effect of temperature on nitrogen uptake was found to be similar to its effect on photosynthesis, with Q 10 values slightly greater than 2. Phytoplankton showed a saturation response to nitrogen (nitrate, ammonium and urea) concentrations, and half-saturation constants were less than 1.0μM. Both of these responses are similar to those found in temperate waters. The coupling of irradiance to nitrogen uptake was significantly different from that of carbon. Ammonium and nitrate uptake saturated at lower irradiances than carbon uptake (<10 vs 30–55 W m −2), and nitrate uptake showed the greatest photoinhibition. A significant amount of ammonium was removed in darkness, which is consistent with the trends observed in field studies. Ratios of carbon:nitrogen uptake throughout the water column were inconsistent with the observed C:N ratios in the particulate matter. The functional relationship between nitrogen uptake and irradiance make estimates of new production in polar waters difficult without a complete understanding of the relationship between carbon and nitrogen uptake.