Iron biogeochemistry in Fram Strait and on the Northeast Greenland Shelf

• Main Author: Krisch, Stephan
• Format: Thesis
• Language: English
• Published: 2021
• Subjects: Arctic; Arctic Ocean; Greenland; Svalbard; Fram Strait; greenlandic; North Atlantic; Phytoplankton; Sea ice; Spitsbergen
• Online Access: https://oceanrep.geomar.de/id/eprint/54783/; https://oceanrep.geomar.de/id/eprint/54783/1/2021_11_17_Fe%20bgc%20in%20Fram%20Strait_PhD%20Thesis_Kurzfassung_Abstract.pdf; https://oceanrep.geomar.de/id/eprint/54783/7/2021_11_17_Fe%20bgc%20in%20Fram%20Strait_PhD%20Thesis.pdf; https://macau.uni-kiel.de/receive/macau_mods_00002124

Fram Strait is the major gateway for Arctic Ocean sea-ice export, and the only deep-water connection between the Arctic Ocean and high latitude North Atlantic. The region is confined by the NE Greenland Shelf to the west and Svalbard to the east; approximately half is covered by summer sea-ice. The bioessential micronutrient iron (Fe) limits primary production across much of the high latitude ocean, including parts of the sub polar North Atlantic south of Fram Strait. Whilst primary production in the Arctic Ocean is generally thought to be controlled by a combination of light and fixed nitrogen availability, the potential role of trace elements as co-limiting factors for phytoplankton growth and their role in ecosystem dynamics has scarcely been investigated. What factors control the supply of Fe to the dynamic Fram Strait region and how does this affect marine primary production? To answer these questions, in late summer 2016, we performed a detailed investigation into the macronutrient and trace element micronutrient distribution across Fram Strait as part of the GEOTRACES GN05 cruise, including full Fe speciation analysis, and conducted nutrient addition bioassay experiments to assess spatial patterns in limiting nutrients. Surface dissolved Fe (dFe), the biologically most accessible form of Fe, showed an east-to-west gradient across Fram Strait. Concentrations were elevated near the Greenlandic coast in proximity to the marine-terminating glaciers Nioghalvfjerdsbrae and Zachariæ Isstrøm, and depleted in the West Spitsbergen Current near Svalbard. Fixed nitrogen (N), the sum of nitrate, nitrite and ammonium, and dFe were deficient in seawater relative to typical phytoplankton requirements. An east to west trend in the relative deficiency of N and Fe was apparent and aligned with phytoplankton responses in bioassay experiments, which showed greatest chlorophyll-a increases in +N treatments near the Greenland continental margin, and +N+Fe near Svalbard. Collectively, our results suggest primary N limitation of ...