Deep Water Formation and Spreading Dynamics in the subpolar North Atlantic from Observations and high-resolution Ocean Models

• Main Author: Handmann, Patricia
• Format: Thesis
• Language: English
• Published: 2019
• Subjects: Labrador Sea; NADW; North Atlantic Deep Water; North Atlantic
• Online Access: https://oceanrep.geomar.de/id/eprint/48432/; https://oceanrep.geomar.de/id/eprint/48432/1/Handmann_thesis.pdf; https://macau.uni-kiel.de/receive/macau_mods_00000258

The subpolar North Atlantic (SPNA) circulation is comprised of a complex interplay between the wind- driven gyre circulation and the buoyancy driven meridional overturning circulation (MOC). As the Atlantic MOC (AMOC) plays an essential role in our climate system due to the associated meridional transport of heat, mass and freshwater it is of fundamental importance to understand its forcing mechanisms, variability and impacts on various different time scales. Due to its role in the formation of North Atlantic Deep Water (NADW), the SPNA is of crucial importance to the understanding of the AMOC. This thesis presents se- lected aspects of the SPNA circulation dynamics, based on various observational data sets in combination with two high-resolution ocean general circulation models (OGCMs; VIKING20, VIKING20X). In order to understand observations in correspondence with OGCM output, the model fidelity in comparison to observed quantities has to be secured. These quantities should be available for sufficiently long time scales and should be determined similarly in the OGCM and the observations. Using observational data in the vicinity of 53◦N in the Labrador Sea and the ocean model VIKING20, the following comparable robust integral quantities were defined: the magnitude and spatial and temporal variability of integral circulation elements on the regional scale (NADW transport at 53◦N; 33 Sv model, 31 Sv observations), the horizontal and vertical extend of the March Mixed Layer Depth in the Labrador Sea and the gyre scale baroclinicity. The models’ boundary current system is more barotropic and indicates stronger monthly to interannual transport variability compared to the observations. Furthermore, during periods of enhanced deep convec- tion an increased correlation between different components of NADW is found in the model, which is found to be the result of a complex modulation of wind stress and buoyancy forcing on regional and basin wide scale. Apart from the challenging to measure AMOC strength, these above ...