Preprints
https://doi.org/10.5194/egusphere-2022-254
https://doi.org/10.5194/egusphere-2022-254
 
17 May 2022
17 May 2022

Tracing the role of Arctic shelf processes in Si and N cycling and export through the Fram Strait: Insights from combined silicon and nitrate isotopes

Margot C. F. Debyser1, Laetitia Pichevin1, Robyn E. Tuerena2, Paul A. Dodd3, Antonia Doncila1, and Raja S. Ganeshram1 Margot C. F. Debyser et al.
  • 1School of Geosciences, University of Edinburgh, Edinburgh, EH9 3FE, United Kingdom
  • 2Scottish Association for Marine Science, Dunstaffnage, PA37 1QA, United Kingdom
  • 3Norwegian Polar Institute, Tromsø, 9296, Norway

Abstract. Nutrient cycles in the Arctic ocean are being altered by changing hydrography, increasing riverine inputs, glacial melt and sea-ice loss due to climate change. In this study, combined isotopic measurements of dissolved nitrate (δ15N-NO3 and δ18O-NO3) and silicon (δ30Si(OH)4) are used to understand the pathways that major nutrients follow through the Arctic ocean. Atlantic waters were found to be isotopically lighter (δ30Si(OH)4= 1.74 ‰) than their polar counterpart (δ30Si(OH)4= 1.85 ‰) owing to partial biological utilisation of dissolved Si (DSi) within the Arctic ocean. Coupled partial benthic denitrification and nitrification on Eurasian Arctic shelves leads to the enrichment of δ15N-NO3 and lighter δ18O-NO3 in the polar surface waters (δ15N-NO3 = 5.44 ‰, δ18O-NO3 = 1.22 ‰) relative to Atlantic waters (δ15N-NO3 = 5.18 ‰, δ18O-NO3 = 2.33 ‰). Using a pan-Arctic DSi isotope dataset we find that the input of isotopically light δ30Si(OH)4 by Arctic rivers and the subsequent partial biological uptake and biogenic Si burial on Eurasian shelves are the key processes that generate the enriched isotopic signatures of DSi exported through Fram Strait. A similar analysis of δ15N-NO3 highlights the role of N-limitation due to denitrification losses on Arctic shelves in generating the excess dissolved silica exported from the Arctic ocean. We estimate that about a third of the dissolved silica exported through Fram Strait is of riverine origin. As the Arctic ocean is N-limited and riverine sources of DSi are increasing faster than nitrogen inputs, a larger export through the Fram Strait is expected in the future. Arctic riverine inputs therefore have the potential to modify the North Atlantic DSi budget and are expected to become more important than variable Pacific and glacial DSi sources over the coming decades.

Margot C. F. Debyser et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2022-254', Anonymous Referee #1, 06 Jun 2022
  • RC2: 'Comment on egusphere-2022-254', Damien Cardinal, 20 Jun 2022
  • RC3: 'Comment on egusphere-2022-254', Anonymous Referee #3, 21 Jun 2022

Margot C. F. Debyser et al.

Margot C. F. Debyser et al.

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Short summary
We focus on the exchange of key nutrients for algae production between the Arctic and Atlantic oceans through the Fram Strait. We show that the export of dissolved silicon here is controlled by availability of nitrate which is, in turn, influenced by denitrification on Arctic shelves. We suggest that any future changes in the river inputs of silica and changes in denitrification due to climate change will impact the amount of silicon exported, with impacts to Atlantic productivity and ecology.