Oceans and Currents

Idaho is about as far from an ocean as you can get in the Northwest. But the ocean still runs your life. It makes about half the oxygen you breathe, drives the weather that brings snow to the mountains, and stores huge amounts of heat that keep the planet livable.

There's really just one connected world ocean, but we divide it into five: the Pacific (biggest and deepest), Atlantic, Indian, Southern (around Antarctica), and Arctic (smallest). Together they cover about 71% of Earth's surface and hold about 97% of its water. The average depth is about 3,700 meters (over 2 miles).

Scientists who study the ocean are called oceanographers.

Rivers slowly dissolve minerals from rocks and carry them to the sea. When ocean water evaporates, the water leaves but the salt stays behind. Undersea volcanoes and vents add more. Over millions of years, the salt built up.

Salinity is the amount of dissolved salt in water. The ocean averages about 35 parts per thousand, or about 3.5% salt. That's roughly a teaspoon of salt in every cup. Salinity is higher where lots of water evaporates (warm, dry places) and lower where rivers, rain, or melting ice add fresh water.

Fun fact: if you could remove all the salt from the ocean and spread it on land, it would make a layer over 150 meters (500 feet) thick.

The ocean is layered by temperature, like a cold drink with ice sinking to the bottom:

• Surface (mixed) layer: warmed by the Sun and stirred by wind. Where most sea life lives.
• Thermocline: a zone where temperature drops quickly with depth.
• Deep zone: cold (near 2 to 4 °C), dark, and under crushing pressure. Below about 1,000 meters, there's no sunlight at all.

Cold, salty water is denser (heavier) than warm, fresh water, so it sinks.

Surface currents are like huge rivers flowing through the top layer of the ocean. They're driven mostly by wind.

Because Earth spins, moving water and air get pushed to the side. This is called the Coriolis effect. In the Northern Hemisphere, currents curve to the right; in the Southern Hemisphere, to the left. That's why big ocean currents form giant loops called gyres. They spin clockwise in the north and counterclockwise in the south.

Currents move heat around the planet:

• Warm currents flow from the equator toward the poles. The Gulf Stream carries warm water up the U.S. East Coast and across to Europe. It's why England is much milder than Canada at the same latitude.
• Cold currents flow from the poles toward the equator. The California Current brings cold water down the West Coast, which is why the beach in California is chilly even in summer.

Gyres also collect floating trash. The Great Pacific Garbage Patch is a huge area of plastic gathered by a Pacific gyre.

Deep currents are driven by differences in density, caused by temperature and salinity. This is called thermohaline circulation (thermo = heat, haline = salt).

Near Greenland and Antarctica, ocean water gets very cold and salty as sea ice forms. It becomes dense, sinks to the bottom, and slowly flows along the ocean floor around the world. Eventually it rises back up and warms. This loop is called the global conveyor belt, and one trip can take about 1,000 years.

The conveyor belt spreads heat, nutrients, and oxygen through the whole ocean. Scientists watch it closely because melting ice adds fresh water, which could slow it down.

In some places, wind pushes surface water away from the coast, and cold, deep water rises to replace it. This upwelling brings up nutrients from the bottom, feeding huge amounts of plankton and fish. Some of the best fishing spots on Earth, like off Peru and California, are upwelling zones.

Every few years, winds over the Pacific weaken and warm water spreads east toward South America. This is El Niño. It changes weather worldwide. Its opposite, La Niña, brings cooler water to the eastern Pacific. These patterns can affect how much snow Idaho's mountains get, which means they affect our rivers, farms, and ski season.