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Title: Inter-decadal changes in stratification and double diffusion in a transatlantic section along 7.5°N
Other Titles: Cambios interdecadales en estratificación y doble difusión en la sección transatlántica 7.5°N
Authors: San Antolín Plaza, Miguel Ángel
Pelegrí Llopart,José Luis 
Machín, Francisco José 
Benítez Barrios, Verónica
UNESCO Clasification: 251007 Oceanografía física
Keywords: Transatlantic section
Neutral buoyancy frequency
Turner angle
Inter-decadal changes, et al
Issue Date: 2012
Project: Memoria Oceánica Del Clima: Flujo de Aguas Intermedias en El Atlántico Austral y Su Transformación en Aguas Superficiales en El Atlántico Ecuatorial. 
Journal: Scientia Marina 
Abstract: We use three transatlantic cruises (1957, 1993 and 2010) along 7.5°N to analyse inter-decadal variations of the neutral buoyancy frequency (with neutral density replacing potential density) and Turner angle. We also use Argo data from the 2003-2011 period to show that, within central and intermediate waters, the changes between the three sections are slightly greater than the seasonal and inter-annual variations, so they may be interpreted as actual inter-decadal variations. The results point to a generalized sinking of isoneutrals between 1957 and 2010, with maximum zonally-averaged values of about 100 m in the central and upper deep layers. They also reveal the occurrence of substantial changes in the intermediate and neighbouring water strata, with differential vertical sinking of isoneutrals and the transformation of their thermohaline characteristics. The neutral buoyancy frequency increased in the lower central and upper intermediate layers and decreased in the lower intermediate and upper deep layers. The distributions of Turner angle highlight a predominance of salt-fingering in the North Atlantic, except for a gravitationally doubly-stable layer located immediately below the intermediate water core; this stable layer thinned substantially between 1957 and 2010 because of the sinking of the lower intermediate isoneutrals acting together with actual water transformations from Antarctic Intermediate Waters into North Atlantic Deep Waters. We conclude that a significant portion of the water column underwent both increased vertical stratification and enhanced salt-fingering, two mechanisms with opposite effects on the effective vertical diffusion.
ISSN: 0214-8358
DOI: 10.3989/scimar.03616.19G
Source: Scientia Marina [ISSN 0214-8358], v. 76 (S1), p. 189-207
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