The nature and effects of ocean turbulence

In the nineteenth and early twentieth centuries, considerable advances were made in understanding the transitional processes that lead from laminar flow towards turbulence. These studies, largely of the onset of flow instability in quiescent flows, were supported by laboratory experiments, sometimes devised and made well after the development of a relevant theory, as explained in the early chapters of this book. Turbulence itself proved a far more difficult subject. Whilst there are the shining examples of Osborne Reynolds' papers in 1883 and 1895, and the insightful use of dimensional reasoning, advances in the understanding of turbulence have been severely constrained and delayed by the analytical complexity of the subject. Only in more recent years have computational methods been devised, and computers of sufficient power developed, to begin at last to replicate the small-scale, high Reynolds number processes that accompany turbulent flow in the ocean.

Technological advances in the last 40 years of the twentieth century, including novel instrumentation, vastly greater capacity of data recorders, faster recording rates, and more reliable and smaller sensors, have formed the basis for relatively rapid advances in the measurement and understanding of turbulence in the ocean. Some of the most important technical developments have been the design and construction of the piezoelectric shear probe to measure velocity shear, thermistors to measure temperature at sub-centimetre scales, and free-fall instruments to carry sensors and measure from near the sea surface to the depths of the abyssal plains, supplemented recently by autonomous vehicles.