Pollutant Transfer and Transport in The Sea

Volume I

Gunnar Kullenberg

• Publisher: CRC Press
• Year: 2018
• Print ISBN: 9781315896755
• eBook ISBN: 9781351092753
• Topic: Biological Sciences
• Subtopic: Biology
• Index: Biological Sciences

This book covers those subject areas considered essential for the transfer and transport of pollutants in the marine environment. This publication will stimulate discussions and interdisciplinary research relevent to pollution problems as well as serve as an educational reference book.

Chapter 1

Physical Processes

Gunnar Kullenberg

Table of Contents

I Introduction

II Characteristics of the Motion

A Mesoscale Fluctuations

B Inertial and Tidal Waves

C Small-Scale Motion

D Vertical Motion

E Fronts

III Features of the General Circulation

A Upper Layer

B Deep Water Circulation

IV Semi-Enclosed Seas

A The Baltic Sea

B Mediterranean Seas

V Features of the Distributions of Properties in the Ocean

A Vertical Distributions of Salinity and Temperature

B Vertical Velocity Distributions

C Vertical Distributions of Contaminants

D Suspended Matter

E Horizontal Distributions

VI Processes Influencing the S, T Distributions

A Vertical

B Horizontal

VII General Equations, Parameters, and Scaling

A General Equations

B Quantification of the Effect of Fluctuations

C Scaling Approaches and Parameters

D Boundary Layers and Stability Considerations

VIII Processes Influencing the Motion

A Shelf Seas

B The Coastal Boundary Layer

C The Open Ocean

IX The Magnitude of Mixing Coefficients

A Vertical Mixing

B Horizontal Mixing

C Ratio of Vertical to Horizontal Mixing

X Energy Sources and Mixing Processes

XI Parameterization of the Mixing

XII Concluding Remarks

Notations

References

I Introduction

The physical transport and transfer of pollutants is determined by the motion in the sea. The motion covers a very large range of scales, from the ocean-wide circulation to molecular motion, distributed over a more or less continuous spectrum (see Figure 1). The spreading, or dispersion, of a passive contaminant is governed by two classes of processes; namely, advection and mixing, sometimes also called diffusion. The advection, i.e., the average velocity over some space or time scale, is caused by relatively large-scale water movements transporting the given property and thus effecting a local change in concentration. The mixing is governed by comparatively small-scale random movements which give rise to a local exchange of the given property without causing any net transport of water. The combined effect of mixing (turbulent diffusion) and advection is here called dispersion.

The theoretical treatment of mixing attempts to relate all the mixing except the part caused by molecular movements (molecular diffusion) to the field of motion in the sea. In order to be able to do this, a detailed knowledge of the field of motion over the complete range of scales is required. At the present this knowledge cannot be obtained practically by means of observations at all scales, and our understanding of the dynamics of the motion is not good enough to permit a deduction of the whole field of motion from observations covering a limited range of scales. Usually it is necessary to rely on averaging procedures whereby a mean current field is defined by the averaging time or space scale which is appropriate for the particular problem.

The definition of a mean and a fluctuating part of the motion requires a separation between the mean and the fluctuating part which will depend to some degree upon the question at hand. In mixing considerations one is often concerned with the effects of small-scale motion, and the fluctuating part may be defined by the scales of motion which contribute significantly to the mean square shear or dissipation scales.

Depending upon the choice of averaging scale, different components of motion (e.g., tidal, meteorological, seasonal) are included in the mean current. The mean current causes advection of the contaminated fluid volume as a whole. The smaller scales perturb the mean motion in a more or less random way. There are different ways of expressing the effect of those scales on the spreading of the contaminant, i.e., to parameterize the mixing or diffusion process. The most common approach is to use effective turbulent exchange coefficients (or eddy diffusion coefficients) analogous to the molecular diffusion coefficients. This is a very crude approach which, however, often has to be relied upon for practical reasons. An alternative approach is to use more sophisticated models of turbulence to close the system of equations.^1,2 This requires an insight into the characteristics of the fluctuating random motion in the sea which is only gradually being obtained.

Figure 1 (A) Distributions of oceanic motion as function of frequency (or period). Eulerian horizontal kinetic energy full drawn at 511 m depth, dashed at 1013 m depth in the western North Atlantic. (From Fofonoff, N. P., Ref. 68—72, Geophysical Fluid Dynamics, Program, Course Lectures and Seminars, Vol. I, Woods Hole Oceanographic Institution, Woods Hole, Mass., 1968. With permission.) (B) Example of kinetic energy density spectrum from the central North Atlantic. (From Gould, W. J., Schmitz, W. J., Jr., and Wunsch, C., Deep Sea Res., 21, 911, 1974. With permission.)

The diffusion generated by fluctuating random motion is generally larger than the molecular diffusion. Therefore the effective turbulent exchange coefficients are not directly influenced by the particular value of the molecular coefficient...

Table of contents

• Cover
• Title Page
• Copyright Page
• Table of Contents
• Chapter 1 Physical Processes
• Chapter 2 Models of Dispersion
• Chapter 3 Experimental Techniques
• Chapter 4 Air-Sea Exchange of Pollutants
• Index