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
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 silicic acid (δ30Si(OH)4) are used to underst...
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Published in | Biogeosciences Vol. 19; no. 23; pp. 5499 - 5520 |
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Main Authors | , , , , , |
Format | Journal Article |
Language | English |
Published |
Katlenburg-Lindau
Copernicus GmbH
06.12.2022
Copernicus Publications |
Subjects | |
Online Access | Get full text |
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Summary: | 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 silicic acid (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 lead 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 silicon exported through Fram
Strait. We estimate that around 40 % of DSi exported in polar surface
waters through Fram Strait is of riverine origin. As the Arctic Ocean is
broadly N-limited and riverine sources of DSi are increasing faster than
nitrogen inputs, a larger silicic acid 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. |
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ISSN: | 1726-4189 1726-4170 1726-4189 |
DOI: | 10.5194/bg-19-5499-2022 |