GEOS1111 – Examination Reading
Joining the Dots
GEOS1111 – Examination Reading
Joining the Dots
If the value of A (in terms of temperature, mass,
rate of a process, etc.) increases, then via a plain
arrow, the temperature, mass, rate of a process,
etc., for B increases. This is a direct cause–effect.
Cause–Effect Type Systems Diagrams
Direct Cause-Effect
An inverse cause–effect is
shown by an arrow with an
attached bullseye, for example,
between B and C.
If B increases, C decreases.
Cause–Effect Type Systems Diagrams
Inverse Cause-Effect
If one traces the path from A to B to
C and back to A, the overall
effect of this loop is that a rise in A
results eventually in a drop in A.
This is negative feedback which
leads to stabilization of the
environment.
Any loop that includes an odd
number of arrows with bullseyes
represents negative feedback.
Negative Feedback
Any combination of arrows with no bullseyes or an
even number of bullseyes represents positive
feedback, or in other words, enhancement of the
original fluctuation and destabilization.
The loop A to B to C to D to A, with two bullseyes,
thus represents positive feedback.
An increase in A results in an increase in B, a
decrease in C, an increase in D, and an increase in A.
Note: The paper has an error “decrease in D”
Positive Feedback
In the final examination
you will be asked questions
about the feedback loops
in this diagram.
Earth’s Systems
Interconnections
GEOS1111 – Examination Reading
Joining the Dots
Kerogen
https://glossary.slb.com/en/terms/k/kerogen#:~:text=Kerogens%20are%20descr
ibed%20as%20Type,material%20that%20typically%20generates%20gas.
Long Term Carbon Cycle
Global
Organic
Carbon
Burial
Consider the loop h–i–j–g.
Increased organic burial raises atmospheric oxygen
(h), which results in a more oxygenated ocean and the
greater burial of phosphorus associated with ferric
oxides (FeP) (i).
Burial of FeP robs the ocean of available dissolved
phosphorus for photosynthesis (j), resulting in a
lower mean phosphorus concentration, and this
results in lowered biological productivity and less
organic burial (g).
This negative feedback loop is thought to be a major
stabilizing control on atmospheric oxygen over a
geological timescale
A System Analysis Example