Nutrient cycling in the Arctic and Subarctic oceans: a stable isotope study

• Main Author: Debyser, Margot
• Other Authors: Ganeshram, Raja, Pichevin, Laetitia, Tuerena, Robyn, UKRI, Changing Arctic Ocean program, SAGES
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: The University of Edinburgh 2023
• Subjects: nutrient; isotope; biogeochemistry; Arctic Ocean; polar; Arctic; Laptev Sea; Pacific; Climate change; Fram Strait; Global warming; laptev; lena river; North Atlantic; Subarctic
• Online Access: https://hdl.handle.net/1842/39796; https://doi.org/10.7488/era/3044

Anthropogenic global warming is actively changing nutrient supply and the food web of the Arctic Ocean and the subpolar regions. This study uses the stable isotopes of dissolved silicon and nitrate, two vital nutrients for marine life, to investigate the marine biogeochemical cycling of nutrients in these regions. This work analyses datasets acquired from 7 oceanographic expeditions in three key regions: the Laptev Sea shelf, polar outflow waters of the Fram Strait (79˚N) and a full transect across the subpolar North Atlantic (50-60˚N). Hydrographic data, alongside concentrations of nitrate (NO3), dissolved silicon (DSi) and their isotopic composition (d15N-NO3, d18O-NO3, d30Si(OH)4) is presented to provide spatially and temporally integrated information on biogeochemical cycling in these regions. The overall objective of this work is to determine the processes which control nutrient budgets and cycling in the Arctic Ocean, export to the subpolar regions and the sensitivity of these processes to ongoing climate change. On the shallow Eurasian shelves of the Arctic Ocean, nitrogen is strongly depleted. This results from intense biological utilisation and significant benthic denitrification in the coastal regions, coupled with nitrogen-poor freshwater sources. Primary production in these regions is limited by N availability as a result of this. This puts a biological control on the extent of DSi utilisation in surface waters and modulates its export to the central Arctic Ocean. Over 40% of riverine DSi supplied by the Lena river is consumed and buried into the sediments of the Laptev shelf, enabled by vigorous recycling of nitrogen. Extrapolating these burial rates to the Eurasian shelf leads to an excess riverine DSi export of 3.10 ± 0.71 kmol/s through the Transpolar Drift to the central Arctic Ocean and outflowing currents. Consequently, Eurasian rivers significantly contribute to the DSi inventory of outflow polar surface waters, providing 40 ± 4% of the total DSi. By contrast, Pacific sources, which were ...