Problem Set 5
Ocean 210, Autumn 2008
SOLUTIONS
1. Note: there were a lot of good and well-written answers to this question. I was
looking for correct physical reasoning when grading, even though clearly there is
not just one correct answer. Nobody really knows what will happen if NADW shuts
off. Here is one possible scenario written by one of you:
a.
i. In the Atlantic Ocean, the movement of deep, cold, salty water southward from
the high northern latitudes would no longer occur. This would result in warmer
temperatures and decreased salinity in the deep sea. The Atlantic Ocean would
thus be less stratified and we may observe increased vertical mixing. Also, deep
waters in the northern hemisphere would be more saline than those in the southern
hemisphere because input from AABW and AAIW would result in fresher waters
at depth in the south.
ii. The NADW has relatively high levels of oxygen because of its origins at the
surface, where oxygen mixes into the ocean from the atmosphere. Because
transportation of these oxygen-rich waters southward would cease, the oxygen
concentration in the Atlantic would drop dramatically. More nutrients would be
present in the deep sea because they would be produced by respiring organisms.
Thus, if NADW formation shut down, the deep Atlantic Ocean would be warmer,
fresher, lower in oxygen, and higher in nutrients.
b.
i. A slow-down of the MOC will decrease the poleward heat flux in the ocean.
ii. The temperature difference between the equator and the poles will increase, i.e.
the equator will get hotter while the poles will get warmer. This is because
excess solar heat absorbed into the ocean at the equator will be distributed to the
heat-deficient poles at a slower rate and this will lead to a build-up of heat and
the equator and an increased deficiency of heat at the poles.
iii. Yes, the atmosphere plays a very important role in the global heat budget. Just
like the ocean, the atmosphere absorbs and transports heat around the globe and
regulates surface temperatures. In order to keep the earth system in radiative
balance, the atmosphere might respond by increasing the amount of heat it
transports to the poles when the ocean heat transport is reduced.
2. Here you will use the mass, temperature and salt balance equations to find the
fraction of NADW, AABW and AAIW. There are many ways to solve for three
equations and three unknowns. Here I will demonstrate one method.
