Primary productivity in Arctic sea ice and Ocean

• Main Author: Fernández-Méndez, Mar
• Other Authors: Boetius, Antje, Waite, Anya
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: Universität Bremen 2014
• Subjects: Arctic; primary productivity; sea-ice algae; nitrogen fixation; carbon cycle; Melosira arctica; 570; 570 Life sciences; biology; ddc:570; Arctic Ocean; Arktis*; Global warming; ice algae; Phytoplankton; Sea ice
• Online Access: https://media.suub.uni-bremen.de/handle/elib/753; https://nbn-resolving.org/urn:nbn:de:gbv:46-00104070-11

Primary productivity in the Arctic Ocean is heavily influenced by sea ice dynamics, which govern light and nutrient availability. Until the last decade, the permanently ice-covered Central Arctic, north of 78ºN, was considered to have low productivity and was often neglected in estimates of primary production in the Arctic. Due to global warming, the Central Arctic is shifting from a perennial to a seasonal ice zone. The reduction in ice cover and thickness leads to an increase in the amount of light that penetrates the ice. In addition, ice melt strengthens stratification that hinders nutrient upwelling, increasing nitrate limitation. Our knowledge about how changes in light and nutrients affect carbon and nutrient budgets in sea-ice algae and phytoplankton is limited, especially in the ice-covered oligotrophic Central Arctic. Understanding the processes that control primary productivity is crucial to predict how the Arctic ecosystem will react to further sea-ice decline. The overall objective of this thesis was to better understand the physical and biological processes that affect primary productivity in the Central Arctic. Specific goals were to investigate i) the role of microbial algal aggregations in carbon and nutrient cycling, ii) the contribution of sea ice to total primary productivity and the impact of sea-ice retreat on annual productivity, and iii) the diversity of nitrogen-fixing bacteria in the Central Arctic. The methods used in this thesis included net primary productivity (NPP) measurements by radioactive carbon (14C) uptake at different irradiances, an irradiance-based model to upscale measured NPP and annual production estimates from the seasonal nutrient drawdown in the mixed layer since last winter. In Chapters I-IV the first specific goal was addressed. Our results showed that sub-ice algal aggregates, such as Melosira arctica filaments, can sink rapidly to the seafloor in early summer when the ice melts contributing to carbon export to the benthos (Chapter I). The aggregates that remain ...