Ali Mashayek Seminar - "Overturning the circulation of the ocean"
Climate Change Research Centre seminar room, level 4 Mathews Building, Kensington Campus, Sydney
It has been an open question whether turbulent vertical mixing across density surfaces is sufficiently large to play a dominant role in closing the deep branch of the ocean meridional overturning circulation. This talk will consist of four parts: (I) By means of a cascade of observationally-tuned nested high resolution realistic numerical simulations of turbulent mixing of tracers in the Southern Ocean I will show that the fast vertical spreading of tracers occurs when they come in contact with mixing hotspots over rough topography. The sparsity of such hotspots is made up for by enhanced tracer residence time in their vicinity due to diffusion toward weak bottom flows; (II) I will further argue that the net vertical mixing in energetic turbulent zones is likely the residual of interior sinking (contrary to the commonly assumed interior upwelling induced by breaking internal waves) and larger boundary upwelling; (III) I will show that the potential implication of these findings is to reshape our understanding of abyssal circulation in a way that may explain the large vertical fluxes of heat and salt required to close the global abyssal circulation; (IV) I will finish by discussing some ongoing work focused on exploring climatic implications of the aforementioned findings.
Brief Biography: Ali Mashayek is a postdoctoral associate at the Marine Physical Laboratory at the Scripps Institution of Oceanography. Prior to that Ali was a postdoctoral fellow at the Department of Earth, Atmosphere and Planetary sciences ( EAPS ) at MIT. He has a PhD in Ocean physics from the University of Toronto. He is interested in the role of turbulence in driving the ocean circulation and its coupling with the atmosphere and the cryosphere at high latitudes. During his PhD Ali studied density stratified turbulence, diapycnal mixing, Southern Ocean eddies, Meridional Overturning Circulation, among other topics.