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Environment
The Emergent Environment of a Virtual Ecosystem
The emergent environment comprises fields of continuously-varying properties, including physical, chemical and demographic variables. The ocean circulation plays an important role in determining the structure of the ecosystem. We use geographically-lagrangian integration to simulate the changes in emergent properties of the ecosystem in a drifting mesocosm.
Diurnal variation
Solar radiation
- reduces the thickness of the surface turbulent layer during the day.
- powers cell division during the day when nutrients are not limiting. (in the mixed layer during spring, or below the nutricline in summer).
- guides the diel migration of zooplankton.
Seasonal variation
The emergent properties of the virtual ecosystem respond strongly to the annual cycle of surface forcing. Here we see the annual variation of the profile of solar heating at noon each day. In clear water, the depth of each isolume would vary sinusoidally with a 12-month period. However the clarity of the seawater is controlled by the concentration of phytoplankton. The water becomes turbid during the spring bloom. The sunlight is absorbed closer to the sea surface. The noon isolumes lie much closer to the sea suface, reducing primary production (self-shading) and the depth range of zooplankton migration (allowing them to forage in the mixed layer during the day while remaining invisible to predators). This is an example of bio-optical feedback in the virtual ecosystem.
The transition from annual to perennial oligotrophy as the mesocosm drifts from Azores to Antilles in six years. [Track 2]
As the ambient climate changes, the mixed becomes shallower, reducing winter nitrogen entrainment from the seasonal thermocline. The uptake of nitrogen declines each year, leading to low primary production and zooplankton starvation.
