Improving the inverse modeling of a trace isotope: how precisely can radium-228 fluxes toward the ocean and submarine groundwater discharge be estimated?
Radium-228 ( 228 Ra), an almost conservative trace isotope in the ocean, supplied from the continental shelves and removed by a known radioactive decay ( T 1∕2 = 5. 75 years), can be used as a proxy to constrain shelf fluxes of other trace elements, such as nutrients, iron, or rare earth elements. I...
Published in: | Biogeosciences |
---|---|
Main Authors: | , , , |
Format: | Text |
Language: | English |
Published: |
2018
|
Subjects: | |
Online Access: | https://doi.org/10.5194/bg-14-3171-2017 https://www.biogeosciences.net/14/3171/2017/ |
id |
ftcopernicus:oai:publications.copernicus.org:bg57107 |
---|---|
record_format |
openpolar |
spelling |
ftcopernicus:oai:publications.copernicus.org:bg57107 2023-05-15T14:58:04+02:00 Improving the inverse modeling of a trace isotope: how precisely can radium-228 fluxes toward the ocean and submarine groundwater discharge be estimated? Gland, Guillaume Mémery, Laurent Aumont, Olivier Resplandy, Laure 2018-09-27 application/pdf https://doi.org/10.5194/bg-14-3171-2017 https://www.biogeosciences.net/14/3171/2017/ eng eng doi:10.5194/bg-14-3171-2017 https://www.biogeosciences.net/14/3171/2017/ eISSN: 1726-4189 Text 2018 ftcopernicus https://doi.org/10.5194/bg-14-3171-2017 2019-12-24T09:51:19Z Radium-228 ( 228 Ra), an almost conservative trace isotope in the ocean, supplied from the continental shelves and removed by a known radioactive decay ( T 1∕2 = 5. 75 years), can be used as a proxy to constrain shelf fluxes of other trace elements, such as nutrients, iron, or rare earth elements. In this study, we perform inverse modeling of a global 228 Ra dataset (including GEOSECS, TTO and GEOTRACES programs, and, for the first time, data from the Arctic and around the Kerguelen Islands) to compute the total 228 Ra fluxes toward the ocean, using the ocean circulation obtained from the NEMO 3.6 model with a 2° resolution. We optimized the inverse calculation (source regions, cost function) and find a global estimate of the 228 Ra fluxes of 8.01–8. 49 × 10 23 atoms yr −1 , more precise and around 20 % lower than previous estimates. The largest fluxes are in the western North Atlantic, the western Pacific and the Indian Ocean, with roughly two-thirds in the Indo-Pacific Basin. An estimate in the Arctic Ocean is provided for the first time (0.43–0.50 × 10 23 atoms yr −1 ). Local misfits between model and data in the Arctic, the Gulf Stream and the Kuroshio regions could result from flaws of the ocean circulation in these regions (resolution, atmospheric forcing). As radium is enriched in groundwater, a large part of the 228 Ra shelf sources comes from submarine groundwater discharge (SGD), a major but poorly known pathway for terrestrial mineral elements, including nutrients, to the ocean. In contrast to the 228 Ra budget, the global estimate of SGD is rather unconstrained, between 1.3 and 14. 7 × 10 13 m 3 yr −1 , due to high uncertainties on the other sources of 228 Ra, especially diffusion from continental shelf sediments. Better precision on SGD cannot be reached by inverse modeling until a proper way to separate the contributions of SGD and diffusive release from sediments at a global scale is found. Text Arctic Arctic Ocean Kerguelen Islands North Atlantic Copernicus Publications: E-Journals Arctic Arctic Ocean Indian Kerguelen Kerguelen Islands Pacific Biogeosciences 14 13 3171 3189 |
institution |
Open Polar |
collection |
Copernicus Publications: E-Journals |
op_collection_id |
ftcopernicus |
language |
English |
description |
Radium-228 ( 228 Ra), an almost conservative trace isotope in the ocean, supplied from the continental shelves and removed by a known radioactive decay ( T 1∕2 = 5. 75 years), can be used as a proxy to constrain shelf fluxes of other trace elements, such as nutrients, iron, or rare earth elements. In this study, we perform inverse modeling of a global 228 Ra dataset (including GEOSECS, TTO and GEOTRACES programs, and, for the first time, data from the Arctic and around the Kerguelen Islands) to compute the total 228 Ra fluxes toward the ocean, using the ocean circulation obtained from the NEMO 3.6 model with a 2° resolution. We optimized the inverse calculation (source regions, cost function) and find a global estimate of the 228 Ra fluxes of 8.01–8. 49 × 10 23 atoms yr −1 , more precise and around 20 % lower than previous estimates. The largest fluxes are in the western North Atlantic, the western Pacific and the Indian Ocean, with roughly two-thirds in the Indo-Pacific Basin. An estimate in the Arctic Ocean is provided for the first time (0.43–0.50 × 10 23 atoms yr −1 ). Local misfits between model and data in the Arctic, the Gulf Stream and the Kuroshio regions could result from flaws of the ocean circulation in these regions (resolution, atmospheric forcing). As radium is enriched in groundwater, a large part of the 228 Ra shelf sources comes from submarine groundwater discharge (SGD), a major but poorly known pathway for terrestrial mineral elements, including nutrients, to the ocean. In contrast to the 228 Ra budget, the global estimate of SGD is rather unconstrained, between 1.3 and 14. 7 × 10 13 m 3 yr −1 , due to high uncertainties on the other sources of 228 Ra, especially diffusion from continental shelf sediments. Better precision on SGD cannot be reached by inverse modeling until a proper way to separate the contributions of SGD and diffusive release from sediments at a global scale is found. |
format |
Text |
author |
Gland, Guillaume Mémery, Laurent Aumont, Olivier Resplandy, Laure |
spellingShingle |
Gland, Guillaume Mémery, Laurent Aumont, Olivier Resplandy, Laure Improving the inverse modeling of a trace isotope: how precisely can radium-228 fluxes toward the ocean and submarine groundwater discharge be estimated? |
author_facet |
Gland, Guillaume Mémery, Laurent Aumont, Olivier Resplandy, Laure |
author_sort |
Gland, Guillaume |
title |
Improving the inverse modeling of a trace isotope: how precisely can radium-228 fluxes toward the ocean and submarine groundwater discharge be estimated? |
title_short |
Improving the inverse modeling of a trace isotope: how precisely can radium-228 fluxes toward the ocean and submarine groundwater discharge be estimated? |
title_full |
Improving the inverse modeling of a trace isotope: how precisely can radium-228 fluxes toward the ocean and submarine groundwater discharge be estimated? |
title_fullStr |
Improving the inverse modeling of a trace isotope: how precisely can radium-228 fluxes toward the ocean and submarine groundwater discharge be estimated? |
title_full_unstemmed |
Improving the inverse modeling of a trace isotope: how precisely can radium-228 fluxes toward the ocean and submarine groundwater discharge be estimated? |
title_sort |
improving the inverse modeling of a trace isotope: how precisely can radium-228 fluxes toward the ocean and submarine groundwater discharge be estimated? |
publishDate |
2018 |
url |
https://doi.org/10.5194/bg-14-3171-2017 https://www.biogeosciences.net/14/3171/2017/ |
geographic |
Arctic Arctic Ocean Indian Kerguelen Kerguelen Islands Pacific |
geographic_facet |
Arctic Arctic Ocean Indian Kerguelen Kerguelen Islands Pacific |
genre |
Arctic Arctic Ocean Kerguelen Islands North Atlantic |
genre_facet |
Arctic Arctic Ocean Kerguelen Islands North Atlantic |
op_source |
eISSN: 1726-4189 |
op_relation |
doi:10.5194/bg-14-3171-2017 https://www.biogeosciences.net/14/3171/2017/ |
op_doi |
https://doi.org/10.5194/bg-14-3171-2017 |
container_title |
Biogeosciences |
container_volume |
14 |
container_issue |
13 |
container_start_page |
3171 |
op_container_end_page |
3189 |
_version_ |
1766330162296651776 |