Seawater Science: Model Ocean Currents in Your Kitchen

An ocean science study from Science Buddies

Key conceptsOcean currentsFluidsDensitySalinityMovementHeat IntroductionUnder the waves the world’s oceans have currents that can move massive amounts of warmer or cooler water from off the coast of one continent to that of another. These currents have profound effects on the continental climates, especially those regions bordering on the ocean. For example, the Gulf Stream (a warm current that flows up from the Gulf of Mexico into the North Atlantic Ocean) likely makes northwestern Europe much warmer than it would otherwise likely be. Have you ever wondered what causes these important currents? In this science activity you will model the behavior of these “rivers” of warm and cold water within the ocean to find out how temperature affects the direction and speed of the currents. BackgroundOcean currents profoundly affect weather and climate, marine transportation and the cycling of nutrients. Deep-ocean currents are driven by differences in the water's density, which is controlled by temperature (cold water is denser than warm water) and salinity (salty water is denser than freshwater). How does the varying density of the ocean's waters create the global currents? To understand the deep-ocean currents, it's easiest to look first at Earth's polar regions. Water flowing into the these regions becomes cold, which increases its density. As ice forms when the water freezes, freshwater is removed from the ocean (it has turned into ice), making the ocean water saltier. The cold water is now denser, due to its lower temperature and the additional salt, so it sinks toward the ocean bottom. Surface water then moves in to replace the sinking water, creating a current. A global “conveyor belt” is set in motion when dense water forms in the North Atlantic, sinks, moves south, circulates around Antarctica and then moves northward to the Indian, Pacific and Atlantic basins. This conveyor belt moves lots of water—it is a huge circulation pattern that transports about 100 times more water than the Amazon River! Although ocean currents depend on temperature and salinity to move, in this activity you will see how temperature alone can create currents in a liquid. Materials

Observations and resultsDid you see the dried thyme leaves move quickly upward when above the flame, then travel horizontally out to the side and slowly fall back down? Because warmer fluid is less dense than cooler fluid, in this activity the fluid heated just above the flame should be less dense than that farther away from the flame. Consequently, the less-dense fluid just above the flame should move upward. When it reaches the surface, it should then move horizontally outward (in all directions, symmetrically). As it flows farther away from the flame and cools, the now-denser fluid slows and sinks back down. At the same time, while the fluid just above the flame moves upward, nearby fluid at the bottom of the dish moves inward, toward the flame to replace the rising fluid—and thus a current is created. This is the pattern you should have observed in this activity by watching the movement of the dried thyme leaves. This movement within a fluid created by less dense matter rising and denser matter sinking is called convection, and is the basis for the global “conveyor belt” of ocean currents. Although lots of water around the world is moved this way, the global conveyor belt moves water slowly, at ten centimeters per second at most, so it can take about 1,000 years for water from the North Atlantic to find its way into the North Pacific! But effects from changes in the conveyor belt's circulation can be felt much more rapidly. CleanupIf you made any oily messes, try cleaning them up with warm water and soap. The vegetable oil and dried thyme leaves mixture made in this activity can be composted or disposed of in the trash (but should not be poured down a drain). More to exploreThermal Convection and Viscosity of a Fluid, from L. W. Braile at Purdue UniversityOcean Currents: Modeling the “Global Conveyor Belt” in Your Kitchen, from Science BuddiesCurrents: The Global Conveyor Belt, from the National Oceanic and Atmospheric AdministrationScience Activities for All Ages!, from Science Buddies

This activity brought to you in partnership with Science Buddies

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