Deep ocean mixing and circulation in subpolar seas

University Of Washington, Seattle WA

Investigators

Abstract

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5). This project is an experimental investigation of oceanic circulation and mixing, particularly focused on the deep ocean at high latitude. Using several new technologies recently developed in the Geophysical Fluid Dynamics (GFD) laboratory at University of Washington the Principal Investigator propose to study the stratified, rotating circulations of the high latitude oceans, particularly aiming at mixing effects, topographic effects and the communication of dense overflow circulations with the surrounding ocean. This work will access a unique data-set from a related NSF-funded field program in the Labrador-Greenland-Iceland-Norway sector of the sub-polar Atlantic Ocean. The predicted decline of the global oceanic overturning circulation, in climate model scenarios, is sensitive to parameterized physics of high-latitude circulation and mixing. The sinking of dense plumes occurs with complex topographic ridges, passages, and basins which are extremely difficult to model numerically. As dense water spills from the Faroe-Bank Channel into the Atlantic for example, intense mixing, entrainment and variability have been recently observed. Over a space of 100 km the water mass is diluted and its place in the global general circulation is greatly altered. Specific experiments, motivated by these observations, will be conducted: (i) pathways and instability of deep, dense boundary currents in topographically complex basins; (ii) mixing and entrainment in deep currents, together with two speculative experiments: (iii) circulation and mixing at the polar front (iv) interaction of internal waves with velocity and density fronts. Intellectual Merit: Research in climate dominantly involves by observations and numerical models. Laboratory experiments in this area are rare, yet we believe there are many reasons for experimenting with real fluids: both in the micro-physics embedded in climate models (like phase change and its effect on dynamics, and turbulent mixing), and in simulation of complex three-dimensional circulations of rotating stratified fluids with complex topography. Beyond climate research, this work on basic potential vorticity dynamics helps in understanding circulations of the atmosphere, and the atmospheres of other planets. Broader impacts: Understanding the ocean climate system is of importance to the larger problem of global warming and its predicted effect in slowing the global ocean circulation. The laboratory has been a source of inspiration for students in our field, for young undergraduates studying the global environment and, through open lectures, to the general public. The University of Washington GFD laboratory is constantly in use as a teaching tool, and is regularly a site of filming science segments for television productions. The project involves several international collaborations: (a) with Professor Afanasyev of Memorial Univ., Newfoundland, Canada on the application of 'optical altimetry' and optical thickness techniques in mapping barotropic and baroclinic circulations in the proposed experiments; (b, with GFD l experiments on downslope flows (Dr. E. Darelius of Univ. Bergen, Norway), dense plumes in valleys like the Faroe Bank Channel, and (c) with GFD laboratory experiments of Dr. O-A. Nøst of Tromsø, Norway, on the pathways of deep circulation in high-latitude basins. This project is contribution to the Atlantic Meridional Overturning Circulation theme of the US CLIVAR (CLImate VARiability and predictability) program.