8 Transport in the Oceans and Coastal Zone
8.1 Introduction
In previous chapters in Part II of this book, we have discussed various motions
of ocean water. The scales of these motions have varied from seconds, for wave
motion, to years, for planetary currents. Ocean water contains, or carries with
it various types of matter such as nutrients, gases, organic and non-organic
particles, and dissolved chemical substances which move with the ocean water.
Here we assume that this matter is passive, which means that it has no ability
to move by its own means with respect to the fluid. Therefore, for example,
the locomotion of marine organisms is excluded from the discussion, and this
problem will be taken up in Chap. 11.
An important and common outcome of the exchange between two volumes
of passive matter which satisfy a conservation law is that a change in the
amount of one element will cause a change in the amount of the other element,
according to the conservation law. For example, an increase in the amount
of element A will cause a decrease in the amount of element B. All variety of
such exchanges constitutes what are known as transport phenomena. In
general, transport phenomena correspond to the transfer of matter, energy
and momentum. Transport of energy and momentum determines the nature
of water motion itself, and in the previous chapters we have shown how the
balance of energy and momentum is included in the governing equations of
water motion.
There are various mechanisms by which matter is transported through the
fluid environment. Probably one of the most important is diffusion. The
concept of diffusion comes from the irregular motion of a group of particles,
which are initially concentrated near some point of space, and after time spread
out, gradually occupying more volume around the initial point. Diffusion is in
fact a random process.
In laminar flow, the transfer of a substance between laminar layers of fluid
is only due to molecular diffusion, which is an extremely inefficient transport
mechanism. However, laminar flow is seldom found in nature. When small
S. R. Massel, Fluid Mechanics for Marine Ecologists
© Springer-Verlag Berlin Heidelberg 1999
8.1 Introduction
In previous chapters in Part II of this book, we have discussed various motions
of ocean water. The scales of these motions have varied from seconds, for wave
motion, to years, for planetary currents. Ocean water contains, or carries with
it various types of matter such as nutrients, gases, organic and non-organic
particles, and dissolved chemical substances which move with the ocean water.
Here we assume that this matter is passive, which means that it has no ability
to move by its own means with respect to the fluid. Therefore, for example,
the locomotion of marine organisms is excluded from the discussion, and this
problem will be taken up in Chap. 11.
An important and common outcome of the exchange between two volumes
of passive matter which satisfy a conservation law is that a change in the
amount of one element will cause a change in the amount of the other element,
according to the conservation law. For example, an increase in the amount
of element A will cause a decrease in the amount of element B. All variety of
such exchanges constitutes what are known as transport phenomena. In
general, transport phenomena correspond to the transfer of matter, energy
and momentum. Transport of energy and momentum determines the nature
of water motion itself, and in the previous chapters we have shown how the
balance of energy and momentum is included in the governing equations of
water motion.
There are various mechanisms by which matter is transported through the
fluid environment. Probably one of the most important is diffusion. The
concept of diffusion comes from the irregular motion of a group of particles,
which are initially concentrated near some point of space, and after time spread
out, gradually occupying more volume around the initial point. Diffusion is in
fact a random process.
In laminar flow, the transfer of a substance between laminar layers of fluid
is only due to molecular diffusion, which is an extremely inefficient transport
mechanism. However, laminar flow is seldom found in nature. When small
S. R. Massel, Fluid Mechanics for Marine Ecologists
© Springer-Verlag Berlin Heidelberg 1999