Cold vs. warm water route – sources for the upper limb of the Atlantic Meridional Overturning Circulation revisited in a high-resolution ocean model
The northward flow of the upper limb of the Atlantic Meridional Overturning Circulation (AMOC) is fed by waters entering the South Atlantic from the Indian Ocean mainly via the Agulhas Current (AC) system and by waters entering from the Pacific through Drake Passage (DP), commonly referred to as the...
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Language: | English |
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Copernicus Publications (EGU)
2019
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Online Access: | https://oceanrep.geomar.de/id/eprint/44873/ https://oceanrep.geomar.de/id/eprint/44873/7/os-15-489-2019.pdf https://doi.org/10.5194/os-15-489-2019 |
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ftoceanrep:oai:oceanrep.geomar.de:44873 2023-05-15T16:02:35+02:00 Cold vs. warm water route – sources for the upper limb of the Atlantic Meridional Overturning Circulation revisited in a high-resolution ocean model Rühs, Siren Schwarzkopf, Franziska U. Speich, Sabrina Biastoch, Arne 2019-05-09 text https://oceanrep.geomar.de/id/eprint/44873/ https://oceanrep.geomar.de/id/eprint/44873/7/os-15-489-2019.pdf https://doi.org/10.5194/os-15-489-2019 en eng Copernicus Publications (EGU) https://oceanrep.geomar.de/id/eprint/44873/7/os-15-489-2019.pdf Rühs, S. , Schwarzkopf, F. U. , Speich, S. and Biastoch, A. (2019) Cold vs. warm water route – sources for the upper limb of the Atlantic Meridional Overturning Circulation revisited in a high-resolution ocean model. Open Access Ocean Science, 15 . pp. 489-512. DOI 10.5194/os-15-489-2019 <https://doi.org/10.5194/os-15-489-2019>. doi:10.5194/os-15-489-2019 cc_by_4.0 info:eu-repo/semantics/openAccess Article PeerReviewed info:eu-repo/semantics/article 2019 ftoceanrep https://doi.org/10.5194/os-15-489-2019 2023-04-07T15:42:30Z The northward flow of the upper limb of the Atlantic Meridional Overturning Circulation (AMOC) is fed by waters entering the South Atlantic from the Indian Ocean mainly via the Agulhas Current (AC) system and by waters entering from the Pacific through Drake Passage (DP), commonly referred to as the “warm” and “cold” water routes, respectively. However, there is no final consensus on the relative importance of these two routes for the upper limb's volume transport and thermohaline properties. In this study we revisited the AC and DP contributions by performing Lagrangian analyses between the two source regions and the North Brazil Current (NBC) at 6∘ S in a realistically forced high-resolution (1∕20∘) ocean model. Our results agree with the prevailing conception that the AC contribution is the major source for the upper limb transport of the AMOC in the tropical South Atlantic. However, they also suggest a non-negligible DP contribution of around 40 %, which is substantially higher than estimates from previous Lagrangian studies with coarser-resolution models but now better matches estimates from Lagrangian observations. Moreover, idealized analyses of decadal changes in the DP and AC contributions indicate that the ongoing increase in Agulhas leakage indeed may have induced an increase in the AC contribution to the upper limb of the AMOC in the tropics, while the DP contribution decreased. In terms of thermohaline properties, our study highlights the fact that the AC and DP contributions cannot be unambiguously distinguished by their temperature, as the commonly adopted terminology may imply, but rather by their salinity when entering the South Atlantic. During their transit towards the NBC the bulk of DP waters experiences a net density loss through a net warming, whereas the bulk of AC waters experiences a slight net density gain through a net increase in salinity. Notably, these density changes are nearly completely captured by Lagrangian particle trajectories that reach the surface mixed layer at least once ... Article in Journal/Newspaper Drake Passage OceanRep (GEOMAR Helmholtz Centre für Ocean Research Kiel) Drake Passage Indian Pacific Ocean Science 15 3 489 512 |
institution |
Open Polar |
collection |
OceanRep (GEOMAR Helmholtz Centre für Ocean Research Kiel) |
op_collection_id |
ftoceanrep |
language |
English |
description |
The northward flow of the upper limb of the Atlantic Meridional Overturning Circulation (AMOC) is fed by waters entering the South Atlantic from the Indian Ocean mainly via the Agulhas Current (AC) system and by waters entering from the Pacific through Drake Passage (DP), commonly referred to as the “warm” and “cold” water routes, respectively. However, there is no final consensus on the relative importance of these two routes for the upper limb's volume transport and thermohaline properties. In this study we revisited the AC and DP contributions by performing Lagrangian analyses between the two source regions and the North Brazil Current (NBC) at 6∘ S in a realistically forced high-resolution (1∕20∘) ocean model. Our results agree with the prevailing conception that the AC contribution is the major source for the upper limb transport of the AMOC in the tropical South Atlantic. However, they also suggest a non-negligible DP contribution of around 40 %, which is substantially higher than estimates from previous Lagrangian studies with coarser-resolution models but now better matches estimates from Lagrangian observations. Moreover, idealized analyses of decadal changes in the DP and AC contributions indicate that the ongoing increase in Agulhas leakage indeed may have induced an increase in the AC contribution to the upper limb of the AMOC in the tropics, while the DP contribution decreased. In terms of thermohaline properties, our study highlights the fact that the AC and DP contributions cannot be unambiguously distinguished by their temperature, as the commonly adopted terminology may imply, but rather by their salinity when entering the South Atlantic. During their transit towards the NBC the bulk of DP waters experiences a net density loss through a net warming, whereas the bulk of AC waters experiences a slight net density gain through a net increase in salinity. Notably, these density changes are nearly completely captured by Lagrangian particle trajectories that reach the surface mixed layer at least once ... |
format |
Article in Journal/Newspaper |
author |
Rühs, Siren Schwarzkopf, Franziska U. Speich, Sabrina Biastoch, Arne |
spellingShingle |
Rühs, Siren Schwarzkopf, Franziska U. Speich, Sabrina Biastoch, Arne Cold vs. warm water route – sources for the upper limb of the Atlantic Meridional Overturning Circulation revisited in a high-resolution ocean model |
author_facet |
Rühs, Siren Schwarzkopf, Franziska U. Speich, Sabrina Biastoch, Arne |
author_sort |
Rühs, Siren |
title |
Cold vs. warm water route – sources for the upper limb of the Atlantic Meridional Overturning Circulation revisited in a high-resolution ocean model |
title_short |
Cold vs. warm water route – sources for the upper limb of the Atlantic Meridional Overturning Circulation revisited in a high-resolution ocean model |
title_full |
Cold vs. warm water route – sources for the upper limb of the Atlantic Meridional Overturning Circulation revisited in a high-resolution ocean model |
title_fullStr |
Cold vs. warm water route – sources for the upper limb of the Atlantic Meridional Overturning Circulation revisited in a high-resolution ocean model |
title_full_unstemmed |
Cold vs. warm water route – sources for the upper limb of the Atlantic Meridional Overturning Circulation revisited in a high-resolution ocean model |
title_sort |
cold vs. warm water route – sources for the upper limb of the atlantic meridional overturning circulation revisited in a high-resolution ocean model |
publisher |
Copernicus Publications (EGU) |
publishDate |
2019 |
url |
https://oceanrep.geomar.de/id/eprint/44873/ https://oceanrep.geomar.de/id/eprint/44873/7/os-15-489-2019.pdf https://doi.org/10.5194/os-15-489-2019 |
geographic |
Drake Passage Indian Pacific |
geographic_facet |
Drake Passage Indian Pacific |
genre |
Drake Passage |
genre_facet |
Drake Passage |
op_relation |
https://oceanrep.geomar.de/id/eprint/44873/7/os-15-489-2019.pdf Rühs, S. , Schwarzkopf, F. U. , Speich, S. and Biastoch, A. (2019) Cold vs. warm water route – sources for the upper limb of the Atlantic Meridional Overturning Circulation revisited in a high-resolution ocean model. Open Access Ocean Science, 15 . pp. 489-512. DOI 10.5194/os-15-489-2019 <https://doi.org/10.5194/os-15-489-2019>. doi:10.5194/os-15-489-2019 |
op_rights |
cc_by_4.0 info:eu-repo/semantics/openAccess |
op_doi |
https://doi.org/10.5194/os-15-489-2019 |
container_title |
Ocean Science |
container_volume |
15 |
container_issue |
3 |
container_start_page |
489 |
op_container_end_page |
512 |
_version_ |
1766398248519467008 |