Arctic freshwater fluxes: sources, tracer budgets and inconsistencies
The net rate of freshwater input to the Arctic Ocean has been calculated in the past by two methods: directly, as the sum of precipitation, evaporation and runoff, an approach hindered by sparsity of measurements, and by the ice and ocean budget method, where the net surface freshwater flux within a...
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Online Access: | https://hdl.handle.net/1956/23786 https://doi.org/10.5194/tc-13-2111-2019 |
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ftunivbergen:oai:bora.uib.no:1956/23786 2023-05-15T14:50:07+02:00 Arctic freshwater fluxes: sources, tracer budgets and inconsistencies Forryan, Alexander Bacon, Sheldon Tsubouchi, Takamasa Torres-Valdes, Sinhue Garabato, Alberto C. Naveira 2020-01-29T14:26:13Z application/pdf https://hdl.handle.net/1956/23786 https://doi.org/10.5194/tc-13-2111-2019 eng eng Copernicus urn:issn:1994-0424 urn:issn:1994-0416 https://hdl.handle.net/1956/23786 https://doi.org/10.5194/tc-13-2111-2019 cristin:1728302 Attribution CC BY http://creativecommons.org/licenses/by/4.0/ Copyright 2019 The Authors The Cryosphere Peer reviewed Journal article 2020 ftunivbergen https://doi.org/10.5194/tc-13-2111-2019 2023-03-14T17:44:32Z The net rate of freshwater input to the Arctic Ocean has been calculated in the past by two methods: directly, as the sum of precipitation, evaporation and runoff, an approach hindered by sparsity of measurements, and by the ice and ocean budget method, where the net surface freshwater flux within a defined boundary is calculated from the rate of dilution of salinity, comparing ocean inflows with ice and ocean outflows. Here a third method is introduced, the geochemical method, as a modification of the budget method. A standard approach uses geochemical tracers (salinity, oxygen isotopes, inorganic nutrients) to compute “source fractions” that quantify a water parcel's constituent proportions of seawater, freshwater of meteoric origin, and either sea ice melt or brine (from the freezing-out of sea ice). The geochemical method combines the source fractions with the boundary velocity field of the budget method to quantify the net flux derived from each source. Here it is shown that the geochemical method generates an Arctic Ocean surface freshwater flux, which is also the meteoric source flux, of 200±44 mSv (1 Sv=106 m3 s−1), statistically indistinguishable from the budget method's 187±44 mSv, so that two different approaches to surface freshwater flux calculation are reconciled. The freshwater export rate of sea ice (40±14 mSv) is similar to the brine export flux, due to the “freshwater deficit” left by the freezing-out of sea ice (60±50 mSv). Inorganic nutrients are used to define Atlantic and Pacific seawater categories, and the results show significant non-conservation, whereby Atlantic seawater is effectively “converted” into Pacific seawater. This is hypothesized to be a consequence of denitrification within the Arctic Ocean, a process likely becoming more important with seasonal sea ice retreat. While inorganic nutrients may now be delivering ambiguous results on seawater origins, they may prove useful to quantify the Arctic Ocean's net denitrification rate. End point degeneracy is also discussed: multiple ... Article in Journal/Newspaper Arctic Arctic Ocean Sea ice The Cryosphere University of Bergen: Bergen Open Research Archive (BORA-UiB) Arctic Arctic Ocean Pacific The Cryosphere 13 8 2111 2131 |
institution |
Open Polar |
collection |
University of Bergen: Bergen Open Research Archive (BORA-UiB) |
op_collection_id |
ftunivbergen |
language |
English |
description |
The net rate of freshwater input to the Arctic Ocean has been calculated in the past by two methods: directly, as the sum of precipitation, evaporation and runoff, an approach hindered by sparsity of measurements, and by the ice and ocean budget method, where the net surface freshwater flux within a defined boundary is calculated from the rate of dilution of salinity, comparing ocean inflows with ice and ocean outflows. Here a third method is introduced, the geochemical method, as a modification of the budget method. A standard approach uses geochemical tracers (salinity, oxygen isotopes, inorganic nutrients) to compute “source fractions” that quantify a water parcel's constituent proportions of seawater, freshwater of meteoric origin, and either sea ice melt or brine (from the freezing-out of sea ice). The geochemical method combines the source fractions with the boundary velocity field of the budget method to quantify the net flux derived from each source. Here it is shown that the geochemical method generates an Arctic Ocean surface freshwater flux, which is also the meteoric source flux, of 200±44 mSv (1 Sv=106 m3 s−1), statistically indistinguishable from the budget method's 187±44 mSv, so that two different approaches to surface freshwater flux calculation are reconciled. The freshwater export rate of sea ice (40±14 mSv) is similar to the brine export flux, due to the “freshwater deficit” left by the freezing-out of sea ice (60±50 mSv). Inorganic nutrients are used to define Atlantic and Pacific seawater categories, and the results show significant non-conservation, whereby Atlantic seawater is effectively “converted” into Pacific seawater. This is hypothesized to be a consequence of denitrification within the Arctic Ocean, a process likely becoming more important with seasonal sea ice retreat. While inorganic nutrients may now be delivering ambiguous results on seawater origins, they may prove useful to quantify the Arctic Ocean's net denitrification rate. End point degeneracy is also discussed: multiple ... |
format |
Article in Journal/Newspaper |
author |
Forryan, Alexander Bacon, Sheldon Tsubouchi, Takamasa Torres-Valdes, Sinhue Garabato, Alberto C. Naveira |
spellingShingle |
Forryan, Alexander Bacon, Sheldon Tsubouchi, Takamasa Torres-Valdes, Sinhue Garabato, Alberto C. Naveira Arctic freshwater fluxes: sources, tracer budgets and inconsistencies |
author_facet |
Forryan, Alexander Bacon, Sheldon Tsubouchi, Takamasa Torres-Valdes, Sinhue Garabato, Alberto C. Naveira |
author_sort |
Forryan, Alexander |
title |
Arctic freshwater fluxes: sources, tracer budgets and inconsistencies |
title_short |
Arctic freshwater fluxes: sources, tracer budgets and inconsistencies |
title_full |
Arctic freshwater fluxes: sources, tracer budgets and inconsistencies |
title_fullStr |
Arctic freshwater fluxes: sources, tracer budgets and inconsistencies |
title_full_unstemmed |
Arctic freshwater fluxes: sources, tracer budgets and inconsistencies |
title_sort |
arctic freshwater fluxes: sources, tracer budgets and inconsistencies |
publisher |
Copernicus |
publishDate |
2020 |
url |
https://hdl.handle.net/1956/23786 https://doi.org/10.5194/tc-13-2111-2019 |
geographic |
Arctic Arctic Ocean Pacific |
geographic_facet |
Arctic Arctic Ocean Pacific |
genre |
Arctic Arctic Ocean Sea ice The Cryosphere |
genre_facet |
Arctic Arctic Ocean Sea ice The Cryosphere |
op_source |
The Cryosphere |
op_relation |
urn:issn:1994-0424 urn:issn:1994-0416 https://hdl.handle.net/1956/23786 https://doi.org/10.5194/tc-13-2111-2019 cristin:1728302 |
op_rights |
Attribution CC BY http://creativecommons.org/licenses/by/4.0/ Copyright 2019 The Authors |
op_doi |
https://doi.org/10.5194/tc-13-2111-2019 |
container_title |
The Cryosphere |
container_volume |
13 |
container_issue |
8 |
container_start_page |
2111 |
op_container_end_page |
2131 |
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1766321184518963200 |