Articles | Volume 12, issue 11
Biogeosciences, 12, 3525–3549, 2015
Biogeosciences, 12, 3525–3549, 2015

Research article 09 Jun 2015

Research article | 09 Jun 2015

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

M. Fernández-Méndez1,2, C. Katlein1, B. Rabe1, M. Nicolaus1, I. Peeken1,3, K. Bakker4, H. Flores1,5, and A. Boetius1,2 M. Fernández-Méndez et al.
  • 1Alfred Wegener Institute Helmholtz Center for Polar and Marine Research, Bremerhaven, Germany
  • 2Max Planck Institute for Marine Microbiology, Bremen, Germany
  • 3MARUM, Center for Marine Environmental Sciences, University of Bremen, Bremen, Germany
  • 4Royal Netherlands Institute for Sea Research, Texel, the Netherlands
  • 5University of Hamburg, Zoological Institute and Zoological Museum, Biocenter Grindel, Hamburg, Germany

Abstract. The ice-covered central Arctic Ocean is characterized by low primary productivity due to light and nutrient limitations. The recent reduction in ice cover has the potential to substantially increase phytoplankton primary production, but little is yet known about the fate of the ice-associated primary production and of the nutrient supply with increasing warming. This study presents results from the central Arctic Ocean collected during summer 2012, when sea-ice extent reached its lowest ever recorded since the onset of satellite observations. Net primary productivity (NPP) was measured in the water column, sea ice and melt ponds by 14CO2 uptake at different irradiances. Photosynthesis vs. irradiance (PI) curves were established in laboratory experiments and used to upscale measured NPP to the deep Eurasian Basin (north of 78° N) using the irradiance-based Central Arctic Ocean Primary Productivity (CAOPP) model. In addition, new annual production has been calculated from the seasonal nutrient drawdown in the mixed layer since last winter. Results show that ice algae can contribute up to 60% to primary production in the central Arctic Ocean at the end of the productive season (August–September). The ice-covered water column has lower NPP rates than open water due to light limitation in late summer. As indicated by the nutrient ratios in the euphotic zone, nitrate was limiting primary production in the deep Eurasian Basin close to the Laptev Sea area, while silicate was the main limiting nutrient at the ice margin near the Atlantic inflow. Although sea-ice cover was substantially reduced in 2012, total annual new production in the Eurasian Basin was 17 ± 7 Tg C yr−1, which is within the range of estimates of previous years. However, when adding the contribution by sub-ice algae, the annual production for the deep Eurasian Basin (north of 78° N) could double previous estimates for that area with a surplus of 16 Tg C yr−1. Our data suggest that sub-ice algae are an important component of the productivity in the ice-covered Eurasian Basin of the central Arctic Ocean. It remains an important question whether their contribution to productivity is on the rise with thinning ice, or whether it will decline due to overall sea-ice retreat and be replaced by phytoplankton.

Short summary
Photosynthetic production in the central Arctic Ocean is controlled by light availability below the ice, nitrate and silicate concentrations in the upper ocean, and the role of sub-ice algae that contributed up to 60% to primary production in summer 2012 during the record sea-ice minimum. As sea ice decreases, an overall change in Arctic PP would be foremost related to a change in the role of the ice algal production and nutrient availability.
Final-revised paper