In this lesson, students apply what they’ve learned about the variations in the water cycle to explore how evaporation affects ocean water density, which in turn affects weather and climate.
Prepared hands-on materials, full year grade-specific curriculum, and personalized live professional development designed to support mastery of current state science standards.
Studying the Ocean’s Saltiness
Since 2011, a satellite called Aquarius has been orbiting Earth from 644 kilometers (400 miles) above the surface. Its mission has been to gather data about the salinity in the surface seawater. Salinity is the measure of all the salts dissolved in water. If you’ve ever gone swimming in the ocean and accidently swallowed some water, you’ve tasted how salty the ocean is.
For hundreds of years, scientists physically measured the salinity of different parts of the ocean from ships and buoys. This provided limited data, however. Some parts of the ocean were much harder for scientists to reach and measure than others. In response to this problem, a team of about 100 scientists and engineers developed and launched the Aquarius satellite in 2011. The Aquarius satellite improves on older methods of gathering data because it continuously monitors and collects data on ocean salinity around the planet.
Understanding the ocean’s salinity, including how that salinity differs around the world and changes over time, is essential for scientists who want to understand the movement of water around the planet. This in turn has major implications for weather and climate. Weather is the conditions of the atmosphere (temperature, humidity, wind speed, and precipitation) at a particular place and time. Climate is the average weather in a location over 30 years or more.
How Oceans Get Salty
Understanding salinity first begins with an understanding of how oceans become salty. Oceans become salty because of interactions among different Earth systems. Remember that a system is a set of connected, interacting parts that form a more complex whole. Systems have inputs and outputs. Inputs are what are received by the system. Outputs are what are sent from the system.
Earth has four primary systems that are interconnected, constantly interacting with and influencing one another—the hydrosphere, atmosphere, biosphere, and geosphere.
Earth’s systems are interconnected, constantly interacting with and influencing one another. For example, all of the water on Earth forms an Earth system called the hydrosphere. The hydrosphere includes all of the ice, liquid water, and water vapor on Earth. It is constantly interacting with another Earth system called the atmosphere. The atmosphere is the mixture of gasses, dust, water vapor, and other molecules above Earth’s crust.
One of the gasses in the atmosphere is carbon dioxide. When water falls to Earth’s surface as rain, it carries some of this carbon dioxide, making the water slightly acidic. This slightly acidic water breaks down the rocks on Earth’s surface into smaller particles, including salt and other minerals. This is an interaction between the hydrosphere and the geosphere—the Earth system made up of Earth’s landforms, including mountains, valleys, soil, and sediment.
All water that collects on Earth’s surface will eventually flow downhill to the oceans because of the pull of Earth’s gravity. As water flows downhill, it carries with it the particles of salt and other matter. All water eventually ends up in the ocean, where it deposits the salt and other matter. Over millions of years, this salt has built up in the oceans, creating the salt water of the oceans.
Why Salinity Matters
Ray Schmitt is the lead scientist on a scientific mission that is using data from the Aquarius satellite. Schmitt has long been fascinated by salt in the ocean. He was one of the first scientists to recognize how important the ocean is in the water cycle.
In 2012, Schmitt and a team of scientists set sail for the world’s saltiest patch of open ocean water, located halfway between the Bahamas and the western coast of North Africa. Scientists say this spot is similar to a desert on land, where there is little rainfall and a lot of evaporation. Data suggest that this spot of ocean is actually becoming saltier over time.
The scientists on board the ship stayed for three weeks, taking measurements on the ocean’s salinity, temperature, and other factors. They used many different kinds of scientific tools, including floats, gliders, drifters, moorings, ships, satellites, and computer models. One of the reasons that scientists care about variations in ocean salinity is that they play a major role in deep ocean currents. Ocean currents are paths of flowing ocean water that push warm and cold water to different parts of the planet.
Cold, dense water in the oceans sinks deep and spreads out all around the world. The sinking water is replaced by the warm, less-dense water near the surface that moves to the north. Scientists call this the Great Ocean Conveyor Belt.
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