The meridional overturning circulation variability and heat content changes in the North Atlantic subpolar gyre

• Main Author: Desbruyères, Damien
• Other Authors: Laboratoire de physique des océans (LPO), Institut de Recherche pour le Développement (IRD)-Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER)-Université de Brest (UBO)-Centre National de la Recherche Scientifique (CNRS), Université de Bretagne occidentale - Brest, Herlé Mercier
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: HAL CCSD 2013
• Subjects: North Atlantic current; Meridional Overturning circulation; Ovide; Subpolar Gyre; Subtropical Gyre; North Atlantic; Variability; ORCA025; ARIANE; Altimetry; Gyre subpolaire; Gyre subtropical; Atlantique Nord; Variabilité; Circulation méridienne de retournement; Courant Nord Atlantique; Altimétrie; [SDU.STU]Sciences of the Universe [physics]/Earth Sciences; Greenland; Labrador Sea; north atlantic current
• Online Access: https://tel.archives-ouvertes.fr/tel-01362211; https://tel.archives-ouvertes.fr/tel-01362211/document; https://tel.archives-ouvertes.fr/tel-01362211/file/These-2013-EDSM-Oceanographie_physique-DESBRUYERES_Damien.pdf

The meridional Overturning Circulation (MOC) of the North Atlantic ocean is a key component of the global climate system, through its role in redistributing heat, freshwater end chemical properties between low and high latitude regions. In mid-high latitude regions, the North Atlantic Current (NAC) forms the upper limb of the MOC. It flows northeastward at the subtropical/subpolar boundary, and splits into two main branches in the eastern subpolar gyre: a northern branch that recirculates within the subpolar region and a southern branch that feed the Nordic Seas.A realistic eddy-permitting simulation (ORCA025-G70, 1/4°) is combined with a Lagrangian analysis tool (ARIANE) to investigate the MOC variability (1965-2004) across the A25-Ovide line, which joins Greenland to Portugal. Two vertical overturning cells are identified: a subtropical cell connecting low and high latitudes (12Sv) and a cell internal to the subpolar gyre (4Sv). The decadal MOC variability is associated with synchronized transport changes of the subtropical and subpolar inflow within the NAC. The latter undergoes important horizontal restructuring with opposed transport changes of its northern and southern branches. Those horizontal transport changes are largely induced by the horizontal variability of the subtropical inflow.Changes in oceanic heat transport across A25-Ovide are largely responsible for the observed heat content changes in the eastern subpolar gyre (1965-2004). Heat transport variability at A25-Ovide results from an imbalance between opposed changes in its velocity and temperature components. Both temperature and velocity anomalies are partly reflected in large scale heaves of isopycnals, and potentially relate to the varying proportion of warm subtropical waters and cold subpolar waters advected within the northern NAC branch.A 2000’s mean full-depth circulation computed along the merged AR7W/A25-Ovide line from repeated hydrographic profile and altimetry data indicates a minor contribution of the Labrador Sea to the basin ...