When you’ve opened the model and are looking at the control panel, first turn off the ffb switch and the land use switch, and then click on the restore all devices button at the lower right.  This will set the model to the pre-industrial state and will not apply: 1) the history of carbon emissions due to fossil fuel burning from 1880 to 2000; and 2) the carbon emissions due to land use changes such as forest burning and soil disruption through plowing.  The model run in this state represents a kind of control model.  If you run it, you’ll see that it is not in a perfect steady state, but the amount of change is negligible.

Part A: The carbon cycle without humans

Experimenting with the Carbon Cycle I

Experiment A1: Changing the alkalinity of the surface ocean.

What happens if we increase the alkalinity of the surface ocean from its starting value of 2.1879 to 2.4?  Remember that alkalinity is related to the sum of positive charge in sea water that must be countered by the negative charges on the carbonate and bicarbonate.  With a given amount of carbon in the sea water, increasing the negative charge can be accomplished by increasing the carbonate (-2 charge) and decreasing the bicarbonate (-1 charge). Decreasing the bicarbonate means less carbon in the carbonic acid form and less carbon in the dissolved gaseous carbon dioxide, which means a lower concentration of CO2 in sea water.  And recall that the exchange of carbon from the ocean to the atmosphere is a function of the relative concentrations.

So, if we increase alkalinity, what will happen to the oceanic pCO2 and the atmospheric pCO2?

Run the model and see what happens.  What is the initial pCO2 of the oceans in this case?

What is the initial pCO2 of the atmosphere?

What happens to the pCO2 values of these two through the 120 years of the model run?

How does global temperature change?

Predict what will happen with the atmospheric and oceanic pCO2 and global temperature if we decrease the alkalinity.

What kinds of natural processes could change the alkalinity of the oceans?

Experiment A2: Changing the strength of the oceanic biologic pump.

Restore the alkalinity to its initial value, then change the biologic pump flow from 10 to 15 (units are Gt C per year).