Vortices Of The Mozambique Ridge Current

Abstract

The seed that eventually gave birth to this thesis was planted in

August, 1975 when, during a cruise of the Research Vessel Meiring Naude

the existence of deep-sea cyclonic vortices in the South Western Indian

Ocean was discovered. Little was it realised during that small, fortuitous

beginning in 1975 that the study would develop into the first detailed

physical oceanographic investigation of the Mozambique Ridge and adjacent

Mozambique Basin areas. It could also not be foreseen that the study would

discover what has been called the Mozambique Ridge Current, and thus

throw new light on the Agulhas Current System as a whole.

From 1976 onwards, the study of these vortices was incorporated

into a project of the National Research Institute for Oceanology of the

Council for Scientific and Industrial Research.

Now, after eight years of data collection and analysis, this thesis

presents the details of the investigation, its objectives, progress and

results. Many of the findings have already been exposed to widespread

scrutiny through national and international publications and seminars, and

this was considered confinnation of the soundness of the investigation.

The presentation of the thesis is separated into three parts. The

function of the first part is to provide a background against which the study

itself can be projected. It contains the aim and scope of the thesis,

a brief literature survey of historic observations, and also a section on

the present state of knowledge of the general circulation in the target

area. The latter section was considered a very important part of the thesis,

since it provides the oceanographic "climate" of the area against which the

phenomena of vortices (oceanographic "weather") can be truly evaluated. The

second part is a detailed presentation of the collection and analysis of the

data (which have been lodged with SADCO, the South African Data Centre for

Oceanography). At the risk of making the thesis too bulky, this part

contains the information on which the third part is based. Some of the

details presented here may therefore seem superfluous to anybody except the

inquisitive reader. A third and conclusive part is a summary and review of

the main results of the thes is, a comparison with local and remote

observations of vortices and a general outlook for the future. It uses the

information of Part II as basis and by intercomparing results serves as the

envelope to bind the various elements of the thesis together.

For the sake of readers who are unfamiliar with operational seagoing

procedures of the National Institute for Oceanology, appendices have

been added to elucidate equipment and methods of data collection and

processing. Other appendices contain vertical sections and information referred

to in the body of the thesis.

The thesis moves in the sphere of mainly descriptive physical

oceanography. We believe that the opportunity for detailed, theoretical

treatment of the features described here lies in the future, and that the

thesis should only act as an introduction to the road eventually leading to a

complete understanding of these phenomena.