Geoscience Reference
In-Depth Information
h
Figure 5.3. “Bathtub” metaphor for the various ways that the concentration of atmospheric
oxygen is regulated; in this case, oxygen levels are expressed as the water height, h, in the
bathtub. the text offers a description of how this works.
it enters. Throw a big bucket of water into the tub. The level will rise in-
stantaneously, causing the water to leave faster. After this initial rise, the
level will drop to the same point as before when input equaled output.
This is known as a negative feedback, and it stabilizes the system. Take
a big bucket of water out of the tub and the opposite happens. The rate
of water leaving the drain slows until the original water level is again
reached. The system has reached a stable state, and this state is main-
tained due to the action of simple feedbacks.
If we open the spigot, a new higher level of water will be reached. The
water level rises and more water will exit the drain to match the new
higher rate of inflow. This is another example of a stabilizing negative
feedback. A higher water level will also be achieved if we constrict the
drain. Conversely, open the drain or reduce the water flow, and a lower
level will be reached. Now, we put in a tube and siphon water out at a
