Primitive Equation Modelling ofPlankton Ecosystems
411
permanently oligotrophic zone. Remember that vertical emigration from the mixed
layer and re-entrainment (immigration) played a key role in the Nogueira at al
(2001) simulation of co-existence of competing diatoms (see 18.9.4).
18.12.4 Conclusion
Virtual Plankton Ecosystems created by Lagrangian Ensemble integration of the
WB food chain model do not exhibit spontaneous (chaotic) instability in plankton
populations. On the contrary, they are robustly stable, relaxing to the demographic
attractor within three years of a quite severe demographic or environmental stress.
This makes the LE method suitable for use in applications that depend on predicting the response of the plankton ecosystem to external disturbances.
18.13 Shallow water VPEs
The Virtual Plankton Ecosystems described above simulate what happens in a
SOO metre water column located in the open ocean, where the depth is much
greater. The bottom boundary condition was open, so detritus and faecal pellets
dropped out into the unresolved deep ocean, carrying carbon and nitrogen out of
the VPE. Many applications are concerned with shallow water, where the sea floor
lies at a depth shallower than SOO metres. Detailed modelling of the shallow water
plankton ecosystem has been undertaken in recent years (see the review by Hofmann & Lascara 1998). A good example of modem practice is ERSEM (Baretta et
aI199S), which is discussed in Chapter 17.
Modifying the LE method to simulate the plankton ecosystem in shallow water
remains a challenge for the future. A starting point will be to modify the existing
WB model. The physics must include a dynamic turbulent boundary layer powered
by tidal or other currents. At some locations the turboclines delimiting the surf ace
and seabed boundary layers will meet, giving a continuous turbulence throughout
the water column. The shallow water model will use LE particles to simulate both
the plankton (dead and alive) and the inorganic sediments. New equations will
describe how both classes of particle can settle on the sea floor, and become re-suspended. Extending the Lagrangian Ensemble method in this way will permit Biological Primitive Equation modelling ofthe plankton ecosystem in shallow water.
18.14 Three-dimensional simulation
18.14.1 Computing
Ali the Virtual Plankton Ecosystems described so far have been designed to
describe what goes on in a water column, based on LE integration of a one-dimensional model. A single-processor UNIX workstation suffices for simple versions of
the WB models. However, when we want to simulate competition, it is necessary to
use many more particles per population (to reduce demographic noise), so the
411
permanently oligotrophic zone. Remember that vertical emigration from the mixed
layer and re-entrainment (immigration) played a key role in the Nogueira at al
(2001) simulation of co-existence of competing diatoms (see 18.9.4).
18.12.4 Conclusion
Virtual Plankton Ecosystems created by Lagrangian Ensemble integration of the
WB food chain model do not exhibit spontaneous (chaotic) instability in plankton
populations. On the contrary, they are robustly stable, relaxing to the demographic
attractor within three years of a quite severe demographic or environmental stress.
This makes the LE method suitable for use in applications that depend on predicting the response of the plankton ecosystem to external disturbances.
18.13 Shallow water VPEs
The Virtual Plankton Ecosystems described above simulate what happens in a
SOO metre water column located in the open ocean, where the depth is much
greater. The bottom boundary condition was open, so detritus and faecal pellets
dropped out into the unresolved deep ocean, carrying carbon and nitrogen out of
the VPE. Many applications are concerned with shallow water, where the sea floor
lies at a depth shallower than SOO metres. Detailed modelling of the shallow water
plankton ecosystem has been undertaken in recent years (see the review by Hofmann & Lascara 1998). A good example of modem practice is ERSEM (Baretta et
aI199S), which is discussed in Chapter 17.
Modifying the LE method to simulate the plankton ecosystem in shallow water
remains a challenge for the future. A starting point will be to modify the existing
WB model. The physics must include a dynamic turbulent boundary layer powered
by tidal or other currents. At some locations the turboclines delimiting the surf ace
and seabed boundary layers will meet, giving a continuous turbulence throughout
the water column. The shallow water model will use LE particles to simulate both
the plankton (dead and alive) and the inorganic sediments. New equations will
describe how both classes of particle can settle on the sea floor, and become re-suspended. Extending the Lagrangian Ensemble method in this way will permit Biological Primitive Equation modelling ofthe plankton ecosystem in shallow water.
18.14 Three-dimensional simulation
18.14.1 Computing
Ali the Virtual Plankton Ecosystems described so far have been designed to
describe what goes on in a water column, based on LE integration of a one-dimensional model. A single-processor UNIX workstation suffices for simple versions of
the WB models. However, when we want to simulate competition, it is necessary to
use many more particles per population (to reduce demographic noise), so the