Photosynthetic production in the central Arctic Ocean during the record sea-ice minimum in 2012

[摘要] The ice-covered central Arctic Ocean is characterized by low primaryproductivity due to light and nutrient limitations. The recent reduction inice cover has the potential to substantially increase phytoplankton primaryproduction, but little is yet known about the fate of the ice-associatedprimary production and of the nutrient supply with increasing warming. Thisstudy presents results from the central Arctic Ocean collected during summer2012, when sea-ice extent reached its lowest ever recorded since the onset of satelliteobservations. Net primary productivity (NPP) was measured in the watercolumn, sea ice and melt ponds by ¹⁴CO₂ uptake at differentirradiances. Photosynthesis vs. irradiance (PI) curves were established inlaboratory experiments and used to upscale measured NPP to the deep EurasianBasin (north of 78° N) using the irradiance-based Central ArcticOcean Primary Productivity (CAOPP) model. In addition, new annual productionhas been calculated from the seasonal nutrient drawdown in the mixed layer sincelast winter. Results show that ice algae can contribute up to 60% toprimary production in the central Arctic Ocean at the end of the productiveseason (August–September). The ice-covered water column has lower NPP ratesthan open water due to light limitation in late summer. As indicated by thenutrient ratios in the euphotic zone, nitrate was limiting primaryproduction in the deep Eurasian Basin close to the Laptev Sea area, whilesilicate was the main limiting nutrient at the ice margin near the Atlanticinflow. Although sea-ice cover was substantially reduced in 2012, totalannual new production in the Eurasian Basin was 17 ± 7 Tg C yr⁻¹,which is within the range of estimates of previous years. However, whenadding the contribution by sub-ice algae, the annual production for the deepEurasian Basin (north of 78° N) could double previous estimatesfor that area with a surplus of 16 Tg C yr⁻¹. Our data suggest thatsub-ice algae are an important component of the productivity in theice-covered Eurasian Basin of the central Arctic Ocean. It remains animportant question whether their contribution to productivity is on the rise withthinning ice, or whether it will decline due to overall sea-ice retreat and bereplaced by phytoplankton.

[学科分类] 地球化学与岩石