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Multidecadal variability of the Mediterranean Overflow Water in the North Atlantic
Stockholm University, Faculty of Science, Department of Meteorology .
Stockholm University, Faculty of Science, Department of Meteorology .
(English)Manuscript (preprint) (Other academic)
Abstract [en]

The Mediterranean overflow water is one of the most important intermediate--depth water masses in the North Atlantic. This water mass, formed in the Mediterranean Sea, produces a saline and warm water tongue at a depth of 1000 m that spreads out from the Strait of Gibraltar and fills a large area of the North Atlantic basin. The production of  this dense water is a result of the excess of evaporation over precipitation and river runoff. A pre-industrial simulation with the earth system model EC-Earth is used to investigate the overflow water. The multidecadal variability of the outflow is analysed by examining the modelled volume and salt transports through the Strait of Gibraltar as well as different atmospheric patterns (such as the wind pattern and the net freshwater fluxes). The salinity evolution in the main core of the outflow in the mid Atlantic is also taken into account.  \ald{The leading empirical orthogonal functions for the modeled salinity 1000 m coincided with the modeled distribution of outflow water}. The associated principal component showed a multidecadal variability of the salinity field. The variability of the net salt transport through the Strait of Gibraltar showed a similar behaviour where the Atlantic--Mediterranean system manifested two clear states. One of these is when the Mediterranean imports salt from the Atlantic and the other is where salt export to the Atlantic predominates. \ald{This result indicates that the Mediterranean Sea acts as a storage of salt alternating between the two states.

Keywords [en]
Salt transport, Strait of Gibraltar, Earth system model, AMOC, NAO
National Category
Earth and Related Environmental Sciences
Research subject
Atmospheric Sciences and Oceanography
Identifiers
URN: urn:nbn:se:su:diva-172841OAI: oai:DiVA.org:su-172841DiVA, id: diva2:1350171
Available from: 2019-09-10 Created: 2019-09-10 Last updated: 2019-09-11Bibliographically approved
In thesis
1. Atmospheric and oceanic circulation from a thermodynamic perspective
Open this publication in new window or tab >>Atmospheric and oceanic circulation from a thermodynamic perspective
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The climate system is continuously transporting and exchanging heat, freshwater, carbon and other tracers in different spatio-temporal scales. Therefore, analysing the system from a thermodynamic or biogeochemical framework is highly convenient. In this thesis the interaction between the ocean and the atmospheric circulation is analysed using thermodynamical and biogeochemical coordinates. Due to the dimensionality of the climate system stream functions are used to reduce this complexity and facilitate the understanding of the different processes that take place. The first half of this thesis, focuses on the interaction between the atmospheric and the ocean circulation from a thermodynamic perspective. We introduce the hydrothermohaline stream function which combines the atmospheric circulation in humidity-potential temperature (hydrothermal) space and the ocean circulation in salinity-temperature coordinates (thermohaline). A scale factor of 7.1 is proposed to link humidity and salinity coordinates. Future scenarios are showing an increase of humidity in the atmosphere due to the increase of temperatures which results in a widening of the hydrothermal stream function along the humidity coordinate. In a similar way, the ocean circulation in the thermohaline space expands along the salinity coordinate. The link between salinity and humidity changes is strongest at net evaporation regions where the gain of water vapour in the atmosphere results in a salinification in the ocean. In addition, the ocean circulation in latitude-carbon space is investigated. By doing so, we are able to distinguish the roles of different water masses and circulation pathways for ocean carbon. We find that the surface waters in the subtropical gyres are the main drivers of the meridional carbon transport in the ocean. By separating the carbon in its different constituents we show that the carbon transported by the majority of the water masses is a result of the solubility pump. The contribution of the biological pump is predominant in the deep Pacific Ocean. The effects of the Mediterranean Overflow Waters on the North Atlantic are discussed in the final part of the thesis.

Place, publisher, year, edition, pages
Stockholm: Department of Meteorology, Stockholm University, 2019. p. 28
Keywords
Atmospheric circulation, Ocean circulation, Stream functions
National Category
Climate Research Meteorology and Atmospheric Sciences Oceanography, Hydrology and Water Resources
Research subject
Atmospheric Sciences and Oceanography
Identifiers
urn:nbn:se:su:diva-172842 (URN)978-91-7797-827-5 (ISBN)978-91-7797-828-2 (ISBN)
Public defence
2019-10-24, De Geersalen, Svante Arrhenius väg 14, Stockolm, 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 2: Manuscript. Paper 3: Manuscript. Paper 4: Manuscript.

Available from: 2019-10-01 Created: 2019-09-10 Last updated: 2019-09-23Bibliographically approved

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