Navigation
Investigating how surface and deep-sea currents transport heat around the globe.
Did you know that a message in a bottle thrown into the ocean off the coast of Florida could travel over 4,000 miles to reach a beach in Norway? How does the ocean move like a giant, invisible highway?
The ocean is never still. The top 10% of the ocean is moved by surface currents, which are primarily driven by global wind patterns. However, these currents don't move in a straight line. Because the Earth is spinning, a phenomenon called the Coriolis Effect deflects the water. In the Northern Hemisphere, currents veer to the right (clockwise), while in the Southern Hemisphere, they veer to the left (counter-clockwise). These large, circular loops of water are called gyres. These gyres act like massive conveyor belts, moving warm water away from the equator and cold water down from the poles.
Quick Check
Which force causes ocean currents to curve instead of moving in a straight line?
Answer
The Coriolis Effect, which is caused by the Earth's rotation.
Below the surface lies the other 90% of the ocean's water. This water moves through thermohaline circulation, also known as the Global Conveyor Belt. This movement is driven by density. Density in the ocean is determined by two main factors: temperature (thermo) and salinity (haline), which is the amount of salt in the water. Cold water is denser than warm water, and salty water is denser than fresh water. In the North Atlantic, water becomes very cold and salty, causing it to sink to the bottom. This 'sinking' pulls more water in to replace it, creating a slow-moving loop that takes about 1,000 years to complete one full circuit around the globe.
Imagine two buckets of water. Bucket A is (warm) and Bucket B is (cold). 1. Because molecules in cold water are packed more tightly, Bucket B is denser. 2. If you pour Bucket B into Bucket A, the cold water will sink to the bottom. 3. This is exactly how the 'pump' for the Global Conveyor Belt works in the Arctic!
Quick Check
What happens to the density of seawater as it gets colder and saltier?
Answer
The density increases, causing the water to sink.
The Gulf Stream is one of the most important surface currents on Earth. It carries warm water from the Gulf of Mexico, up the U.S. East Coast, and across the Atlantic toward Europe. This current acts like a giant 'space heater' for countries like the United Kingdom and Norway. Even though London is at the same latitude as parts of Canada that are covered in snow for half the year, the Gulf Stream keeps London's climate mild and rainy. Without this heat transport, Western Europe's average temperatures could drop by as much as to .
Let's compare two cities at roughly the same latitude (): 1. London, UK: Average January temperature is about (). 2. Calgary, Canada: Average January temperature is about (). 3. The difference is primarily due to the Gulf Stream releasing heat into the atmosphere over Europe.
Climate change is causing Arctic ice to melt. This adds massive amounts of fresh water to the North Atlantic. 1. Fresh water is less dense than salt water (). 2. If the water isn't salty enough, it won't sink. 3. If the water doesn't sink, the 'pump' for the Global Conveyor Belt could slow down or stop, potentially freezing parts of Europe while the rest of the world warms.
In the Northern Hemisphere, the Coriolis Effect causes surface currents to curve in which direction?
What does the 'haline' in thermohaline circulation refer to?
If the Global Conveyor Belt slowed down, Western Europe would likely become warmer.
Review Tomorrow
In 24 hours, try to explain to someone else how salt and temperature work together to move water at the bottom of the ocean.
Practice Activity
Look at a world map and find your closest coastline. Research which major ocean current flows near it and whether it brings warm or cold water.