Plants are involved in the GEOCARB models in three ways:
Part of my project is to improve the representation of plant
weathering in models such as GEOCARB. To do this, I will be
using the results of experiments conducted by other members of
our team and attempting to model the weathering chemistry.
- There is a weathering effectiveness function which
changes as a function of plant evolution. This function is
used to scale the carbon fluxes, which means it multiplies
them. It is normalised to the preindustrial present, so that today's
weathering effectiveness is 1.0. Smaller values
express the assumed weathering effectiveness of an entirely
herbaceous or lichen-dominated flora (as in the early Palaeozoic),
and forests dominated by gymnosperms. There are transition
periods during which these values are linearly interpolated.
These are currently 380-350 Ma (million years ago) for the advent of
forests, and 130-80 Ma for the spread of angiosperms.
- The biological weathering feedback function expresses
the extent to which CO2 values are suppressed in
the atmosphere as a result of weathering (ie it is a negative
feedback). In GEOCARB, the feedback due to forests is assumed to
vary according to the carboxylase action of Rubisco, under the
assumption that the productivity of
only 35% of the world's plants are limited by atmospheric CO2.
Before forests, in the early Palaeozoic, a compromise function is
assumed between abiotic CO2-limited weathering
and possible microbial
weathering (Berner 1992). The transition period is the same as that for
the advent of
forests for the weathering effectiveness function.
- Plants also contribute material to the organic
reservoir, eg coal.
This is not part of my project.