Introduction

The properties of dispersants

The objective of this chapter is to describe some of the ideas and observations that have been devised to assess and quantify rates of turbulence dispersion in the ocean.

There are several reasons why dispersion, introduced in Section 1.5.1, is of importance in the ocean. It is dispersion that determines the distribution of the naturally occurring ‘tracers’, such as salinity, for example the area within the North Atlantic that is affected by the high salinity emanating from the Mediterranean through the Straits of Gibraltar (Fig. 5.1). The volume of the water column in the Pacific affected by the plume containing helium 3 (3He) coming from hydrothermal vents in the East Pacific Rise (Fig. 5.2) is a consequence of several processes of dispersion, notably in the initial buoyant ascent of the plume, including the entrainment of surrounding water, and the subsequent advection and spread in the stratified ocean of the water ‘labelled’ by the 3He. In many cases, especially those relating to the accidental discharge of toxic chemicals or oil into the sea or the development and spread of harmful algal blooms (HABs; Fig. 5.3), the dispersion of solutes or particles by turbulent motion may have dire consequences as the pollutants spread to sensitive regions, especially those near shore where there can be a detrimental effect on mariculture, human health and recreation. Prediction is therefore of great practical importance.