PASCO ME-6816 User Manual
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Top Valve
Bottom Valve
Val ve
Handles
1 Liter Reservoir
1 Liter Reservoir
Milliliter
Scale
Centimeter
Scale
Pouring Spout
Instruction Manual
012-12254A
*012-12254*
PASCO Earth Science
Density Circulation Model
ME-6816
800-772-8700 www.pasco.com
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Density Circulation Model ME-6816
Recommended Equipment* Other Items
PASPORT Temperature Sensor (PS-2125 or equivalent) Water
PASPORT Salinity Sensor (PS-2195) Ice cubes
PASPORT® Interface Salt, reagent grade (non-iodized)
PASCO Data Acquisition Software Food coloring (or equivalent)
*See the PASCO catalog or PASCO web site at www.pasco.com for more information.
Introduction
The Density Circulation Model consists of two one-liter reservoirs connected by two valves. Each reservoir has a milliliter (mL)
scale on one side and a centimeter (cm) scale on the other side for measuring volume and depth. The reservoirs feature pouring
spouts on three sides.
When the valve handles are vertical, the valves are closed. Turn a handle so it is horizontal in order to open the valve.
The Density Circulation Model is designed to allow students to investigate the circulation of fluids with different densities due to
conditions such as differences in temperature or differences in salinity.
Background
Temperature and Salinity
Two of the most important characteristics of Earth’s oceans are the temperature and salinity (salt content) of the water. Together,
temperature and salinity determine the density of the water, which is a major factor controlling the circulation and vertical movement of ocean water. Density-driven circulation accounts for 90% of all the movement of water (currents) in the oceans. Water
movement of this type is also called thermohaline circulation (“thermo” for temperature and “haline” for salinity). Colder and saltier water is heavier than warmer, fresher water. Water gets denser in higher latitudes due to the cooling of the atmosphere and the
increased salt levels, which result from the freezing of surface water. (Frozen water normally contains mostly freshwater, leaving
higher concentrations of salt in the water that remains liquid.) The polar regions have very dense, very cold, and very salty water.
Evaporation can also cause an increase in salinity. As sea water evaporates, the salt is left behind, increasing the salinity. (The
Mediterranean Sea is an example of an area where this happens.)
The global average for sea-water temperature is 3.51 °C. Although surface water temperatures can range from 10 °C to 25 °C,
about 77 percent of the water in the oceans is cooler than 4 °C. The global average for salinity is 34.72 grams (g) of dissolved solids per kilogram (kg) of seawater. Most of the water in the ocean is in the narrow salinity range of 33.8 to 36.8 g/kg.
Differences in water density generate slow moving currents due to the sinking of the colder, saltier water into deeper parts of the
oceans' basins and the displacement of lighter, less salty water upward. Deep water currents move very slowly, usually around 1
meter per hour (0.001 km/h), compared to wind-driven surface water currents that move at about 1 km per hour (0.6 miles per
hour). Dense water will sink until it reaches an area of even denser water. The water will then spread horizontally as more water
sinks behind it. For example, Antarctic Bottom Water, formed along the coast of Antarctica, will sink below less dense water as it
makes its way north toward the equator. As the dense water moves north, it is warmed by the surrounding water. As it warms and
becomes less dense, the water will rise toward the surface. This upwelling of water from the polar regions provides essential nutrients for phytoplankton which live closer to the surface, and phytoplankton is the beginning of the food chain for many of the creatures in the ocean.
Ocean Layers
The ocean has layers of water that differ in temperature. Overall, there is a three layered thermal structure in most of the ocean. The
lop layer of water is called the mixed layer. The sun-warmed surface water mixes with cooler, deeper water due to winds, breaking
waves, and turbulent currents. Below the mixed layer is the main thermocline that extends down about 1,000 m. The temperature
in this layer changes rapidly with depth. The main themocline separates the warmer mixed layer from the cooler deep layer that
extends to the ocean floor).
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ME-6816 012-12254A Theory
Theory
• Water density is affected by temperature and salinity, resulting in deep water currents in the ocean.
Procedure
Temperature Differences
Prepare the water
You will need a hot plate, two containers (one-liter or larger), water, ice cubes, a stirring rod, and food coloring.
• Fill one of the containers with one liter of cool water and add six ice cubes. Stir the water until all of the ice melts.
• At the same time, fill the other container with one liter of water and place the container on the hot plate. Stir the water as it
warms up to at least 10 ° C above room temperature.
Prepare the chambers
• Start with the top and bottom valves closed on the Density Circulation Model.
• Add one liter of the ice cold water to one reservoir and add one liter of warm water to the other reservoir. Stir the water in each
chamber to make sure they are homogeneous.
• Add a few drops of food coloring to each reservoir. Stir if necessary.
• Allow the model to sit very still for a few minutes.
Observe and Record
1. Open the top and bottom valves to allow circulation.
2. Observe the movement of the more dense, cooler water and the less dense, warmer water.
3. Record what happens in both reservoirs.
Salinity Differences
• Start with the top and bottom valves open. Add cool tap water to each reservoir until the water level is at 1 liter for both. Close
the top and bottom valves after you add the water.
• Instead of ice, add about 200 g of salt to one of the reservoirs. Use a stirring rod or long handle spoon to stir the salt and water
until all of the salt is dissolved. Follow the same procedure as for water.
1. Allow the model to sit very still for a few minutes. Add a few drops of food coloring to each reservoir.
2. Open the top and bottom valves to allow circulation.
3. Observe the movement of the more dense, saltier water and the less dense, fresh water.
4. Record what happens in both reservoirs.
Using the Model with a Temperature Sensor
Equipment Setup
1. If you are using a computer, connect a PASCO interface to the computer, turn on the interface, and turn on the computer.
If you are using a stand alone interface, turn on the PASCO interface.
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