Introduction

My long term objectives are to improve our understanding and ability to quantitatively measure ocean mixing. The ocean is affected by mixing in at least two ways:

1. Climate. The "global ocean conveyor belt" transfers warm low-latitude waters to higher latitudes where the heat is released, cooling the tropics and warming the temperate zones. Due to the high heat capacity of water, the upper 1 m of ocean carries about the same heat energy as the entire atmosphere, so that heat storage and transport by the ocean controls climate, particularly in maritime areas. The oceanic poleward heat flux and the timing of ocean response to atmospheric warming are both very sensitive to rates of ocean mixing (Solokov and Stone, 1998) such that the uncertainties in mixing are comparable with other uncertainties involved in climate prediction.

2. Ecological health. The ocean recycles and stores nutrients that supply the growth of marine phytoplankton, which "...generate roughly half the planetary primary production, affect the abundance and diversity of marine organisms, drive marine ecosystem functioning, set upper limits to fishery yields", and "...influence climate processes and bio-geochemical cycles." (Boyce et al, 2010). Ocean mixing modulates the supply of nutrients to the photic zone, and controls the upper ocean density stratification that supports phytoplankton growth. Recent observed declines in ocean health (DFO, 2010) have a variety of likely causes, but may originate in part from the global-scale decline in phytoplankton abundance noted by Boyce et al (2010).

Ocean mixing is driven by several physical ocean processes that receive energy from large scales and use that energy to drive turbulent mixing: internal waves, thermohaline intrusions, and shear instabilities, to name a few. We quantify the present rate of ocean mixing by directly measuring turbulence (Oakey, 1982, Ruddick, Anis and Thompson, 2000), but the only way to predict the changes in ocean mixing due to upcoming changes in our ocean climate is via observational process studies and models that link ocean turbulence to larger scale phenomena such as thermohaline intrusions (Ruddick, Oakey, and Hebert, 2010). In addition to using laboratory tank experiments to simulate ocean mixing processes, my colleagues and I are developing new ways to visualize and understand mixing processes, using sound, billions of tiny tracer particles, and laser beams.