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The response of the central Arctic Ocean stratification to freshwater perturbations
Swedish Meteorological and Hydrological Institute, Gothenburg, Sweden.
Stockholm University, Faculty of Science, Department of Meteorology .
Number of Authors: 2
2016 (English)In: Journal of Geophysical Research - Oceans, ISSN 2169-9275, E-ISSN 2169-9291, Vol. 121, no 1, 792-817 p.Article in journal (Refereed) Published
Abstract [en]

Using a state-of-the-art coupled ice-ocean-circulation model, we perform a number of sensitivity experiments to examine how the central Arctic Ocean stratification responds to changes in river runoff and precipitation. The simulations yield marked changes in the cold halocline and the Arctic Atlantic layer. Increased precipitation yields a warming of the Atlantic layer, which primarily is an advective signal, propagated through the St. Anna Trough, reflecting air-sea heat flux changes over the Barents Sea. As the freshwater supply is increased, the anticyclonic Beaufort Gyre is weakened and a greater proportion of the Arctic Ocean freshwater is exported via the Fram Strait, with nearly compensating export decreases through the Canadian Arctic Archipelago. The corresponding reorganization of the freshwater pool appears to be controlled by advective processes, rather than by the local changes in the surface freshwater flux. A simple conceptual model of the Arctic Ocean, based on a geostrophically controlled discharge of the low-salinity water, is introduced and compared with the simulations. Key predictions of the conceptual model are that the halocline depth should decrease with increasing freshwater input and that the Arctic Ocean freshwater storage should increase proportionally to the square root of the freshwater input, which are in broad qualitative agreement with the sensitivity experiments. However, the model-simulated rate of increase of the freshwater storage is weaker, indicating that effects related to wind forcing and rerouting of the freshwater-transport pathways play an important role for the dynamics of the Arctic Ocean freshwater storage.

Place, publisher, year, edition, pages
2016. Vol. 121, no 1, 792-817 p.
Keyword [en]
Arctic Ocean, halocline, freshwater, conceptual model, ocean model, Atlantic water
National Category
Earth and Related Environmental Sciences
Research subject
Atmospheric Sciences and Oceanography
Identifiers
URN: urn:nbn:se:su:diva-128572DOI: 10.1002/2015JC011003ISI: 000371432200046OAI: oai:DiVA.org:su-128572DiVA: diva2:935541
Available from: 2016-06-10 Created: 2016-03-30 Last updated: 2017-03-03Bibliographically approved
In thesis
1. Freshwater processes and water mass transformation in the Arctic Ocean
Open this publication in new window or tab >>Freshwater processes and water mass transformation in the Arctic Ocean
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis explores freshwater-related processes and water mass transformation in the Arctic Ocean. Knowledge of these processes is important from both a local and a global perspective. Globally, because the export of cold and low saline water and sea ice might influence the North Atlantic and global meridional overturning circulation. Locally, because freshwater processes affect the vertical stratification and permit favorable conditions for the ice cover.

Models of different complexity are the main tools of the present work. A part of the material considers how these models can be used to examine the key processes governing freshwater balance. Additionally, the freshwater budgets amongst 10 different ocean general circulation models (OGCMs) are compared and robust features and weaknesses identified.

A large part considers the freshwater processes governing the stratification with an emphasis on the low saline upper parts. The interactions between freshwater sources and sinks are studied in an OGCM using passive tracers. It is found that the composition, pathways and shelf-basin exchange of low saline water primarily involve processes linked to Siberian runoff, Pacific water and sea-ice melting and formation. Motivated by observed changes and paleorecords the sensitivity of the stratification is further explored in freshwater perturbation experiments with an OGCM. The response yields a deeper halocline for decreasing freshwater input, in line with a theoretical model.

The final part focuses on a new framework for analyzing water mass transformations. In the framework volume, heat and salt budgets are computed in salinity-temperature space. Using different OGCMs it is shown how surface and interior processes transform inflowing waters towards colder and fresher waters and how the halocline renewal rate can be estimated. Limiting cases for the water mass transformation balance are identified by separating contributions from surface, internal and boundary fluxes.

Place, publisher, year, edition, pages
Stockholm: Department of Meteorology, Stockholm University, 2014. 44 p.
National Category
Oceanography, Hydrology, Water Resources
Research subject
Atmospheric Sciences and Oceanography
Identifiers
urn:nbn:se:su:diva-107594 (URN)978-91-7447-998-0 (ISBN)
Public defence
2014-11-05, De Geersalen, Geovetenskapens hus, Svante Arrhenius väg 14, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Submitted. Paper 4: Manuscript.

Available from: 2014-10-14 Created: 2014-09-22 Last updated: 2017-03-03Bibliographically approved

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