Thermohaline Circulation

Outside Links: Lab Guide

Experimental Setup:

Our experimental setup consisted of a square clear 16” x 16” tank set on a turntable. A sloping bottom (β-plane) was created with a piece of rectangular plastic to simulate the sphericity of the earth. We attached a tower to one side of the tank to be filled with dyed water. The tank was filled to 2 inches above the β-plane at its elevated edge with tap water using a bucket. The tank was allowed to reach solid body rotation for at least 20 minutes for every attempt. Using a plastic bin and two lewis clamps, we built a platform to house our water tower on the shallow side (Figure 1). Water in the tower was dyed red, using red food coloring, and allowed to rotate with the tank.

To transfer water from the storage tower, we used a siphon tube system with a diffuser attached to one end of the tube. The siphon system was completely submerged in the storage tower to allow the dyed water to fill the tube. Once the tubing was completely filled, a clamp was used to prevent any siphoning flow as the diffuser was placed into the corner of the rotating tank. Tape was used to secure the diffuser to the edge of the rotating tank. Additional tape was stretched across the storage tower to prevent the tubing from floating and filling with air. At this point, the tank was allowed to rotate for at least 20 minutes to reach required steady-state.

To begin the experiment and transfer of dyed water, the clamp on the tubing was released to allow the water to slowly enter into the rotating tank via the diffuser. All the water in the storage tank was allowed to diffuse (approximately 15 minutes).

Experimental Settup.JPG
Experimental Settup.JPG
Figure 2. 2015 Experimental Setup

Figure 1. Experimental Setup


The primary issue we encountered in the experiment was that not all the items required for the experimental setup were present. Since we did not have a valve to control the siphoning flow, we fabricated a valve by crimping the tube with a lewis clamp. This worked well for the purpose of controlling the flow of water from the storage tank. Another issue we encountered was that the extra weight from the tower unbalanced the tank, causing problems with rotation. This did not seem to affect the experiment, but may have added extra stress, especially at high speeds.

Real World Examples:

The Younger Dryas are a period where there might have been sufficient freshwater in the northern oceans to slow thermohaline circulation. During the last glacial period, the globe experienced massive and abrupt temperature shifts. The Younger Dryas event, characterized by cooling of up to 8°C, was triggered by massive freshwater discharge from ice sheets into the North Atlantic surface ocean. This freshwater “cap” formed an impenetrable layer on the surface that prevented deep water formation, diffusion of heat, and “pushing” on deep water, halting abyssal circulation. As a result, heat was not distributed from the equator, via the conveyor belt, thus high latitudes experienced intense cooling.

This begs the question: what will happen as global temperatures rise and freshwater input increases as polar ice melts? The difference between the Younger Dryas period, which occurred 11,000 years ago, and current global trends is a matter of freshwater source. During the Younger Dryas, freshwater spilled into the North Atlantic from a massive pool of water that was growing over the Laurentide ice cap (present day Canada). Today, we observe the annual decrease in arctic sea ice and the Greenland ice sheet, and an increasing flux of fresher water. This has led to a number of proposed ‘ice-age scenarios’ where ocean circulation shuts down, and less heat is transported northward from the tropics. In reality, the decreased influx of heat in these areas would be more than compensated for by atmospheric warming from the Greenhouse Effect. It is possible however, that this weakening of thermohaline circulation could have other serious effects including warming in the Antarctic and cooling in the North Atlantic. Decreased circulation could also shift the thermal equator southward along with the tropical rain belts, drastically altering weather patterns. Upwelling could also decrease, depriving some marine ecosystems of essential nutrients.

Deep Western Boundary Current can be seen with CFC tracer. MOVE moorings.


-valve for controlling flow was not among the material we had, substituted a clamp
-balance the side opposite the tower with more weight OR mount dyed water tank on camera stand above main tank
-experiment can be done without a diffuser as long as siphon flow rate is slow (2 mL/min)
-used 1 L rectangular incubation flask to prop up white sheet to make slope and wedge the sheet to be flush with the high slope side of the tank
-using very hot water can disrupt the circulation