The Gulf Stream Extension Region: Its dynamics and interaction with the atmosphere

• Main Author: Claus, Martin
• Format: Thesis
• Language: English
• Published: 2011
• Subjects: Separation Point; Newfoundland
• Online Access: https://oceanrep.geomar.de/id/eprint/12505/; https://oceanrep.geomar.de/id/eprint/12505/1/thesis.pdf

The Gulf Stream Extension Region is a key region for meridional heat transport of the Earth system. Its importance for the climate and for seasonal prediction has been increasingly recognized in recent years. However, the dynamics of the ocean in this region are not understood sufficiently. There are basically three mechanisms to explain the observed increase of barotropic transport and the formation of recirculation gyres in the Gulf Stream Extension Region: (i) advection of potential vorticity, (ii) Joint Effect of Baroclinicity and Relief and (iii) eddy momentum flux, of which the latter is investigated in the present work. 16 years of satellite derived surface velocities of weekly resolution are used to compute the eddy momentum flux and its seasonal and NAO related variability. These fluxes were used to drive a diagnostic linear shallow water model to estimate the mean barotropic transport and its variability associated with turbulent momentum flux. The results show that eddy momentum flux is able to drive significant transport in the Gulf Stream Extension Region, enough to explain its observed increase. The barotropic transport streamfunction exhibits northern and southern recirculation gyres between the separation point at Cape Hatteras and the Newfoundland Ridge and also resemble mesoscale circulation features like the Mann eddy. The seasonal transport variability is shown to be large upstream of the Grand Banks of Newfoundland with the strongest signal where the Gulf Stream crosses the New England Seamounts at about 62°W. The NAO appears to significantly affect the strength of the northern and southern recirculation gyres during the winter season leading to an increased mean transport in winters with a positive NAO index.