Why is the Pacific Ocean higher than the Atlantic Ocean, and how does this affect the Panama Canal

Between the Pacific Ocean and the Atlantic Ocean there is an elevation difference of about 20 cm.

Although it may seem like a subtle difference, it has important implications for ocean circulation, global climate, navigation, and even major engineering feats like the Panama Canal.

This is taken into account when establishing ship routes, offshore oil operations, fishing, search and rescue, oil spill countermeasures and offshore operations.

You may be surprised to learn that the waters in Chile, Peru, Ecuador or Colombia are higher than those in Argentina, Brazil or Uruguay.

The Atlantic and Pacific oceans are connected and form a continuous mass of salt water that covers more than 71% of the Earth's surface.

But if it is continuous, how do scientists know that there is a difference in height?

“Sea surface height is a factor that can be studied from space,” Susana Buchan, an oceanographer and visiting professor at the University of Concepcion in Chile, tells BBC Mundo.

He adds: “Using satellites, you can study temperature and chlorophyll… These are the parameters that we usually see from space to understand the different physical processes that occur in the ocean and that affect marine life.”

To get a complete picture of the marine terrain, in addition to the network of tide gauges that determine sea level at specific points, scientists use satellite measurements.

Altimetry satellites, such as NASA and ESA's Jason 3, send radar pulses toward the sea surface and measure the time it takes for the signal to return.

This information allows the ocean surface height to be calculated with an accuracy of a few centimetres.

The data, collected over decades, allows detailed models of the sea surface to be created and reveals differences in elevation on a global scale.

There is a combination of several elements that explains this difference.

Some affect more than others. For example, tides or underwater volcanic activity can temporarily affect sea surface height.

But there are forces that make the height difference permanent. Check out some of them below.

The most famous example that experts use to explain this phenomenon is water and olive oil. If we put the two elements in a cup, we immediately see that the oil – which is the least dense – floats.

“It's very simple. The example of olive oil shows this, but if we transfer it to what happens in the ocean, let's say we put salt water in one cup and fresh water in the other and connect the two containers at the bottom with another small hose,” says Osvaldo Ulloa, director of the Millennium Science Institute. Oceans in Chile, he is also an academic at the University of Concepcion.

“So one might think that saltwater and freshwater would meet at the midpoint, but that's not the case,” he explains. “They will move slightly toward freshwater, because the pressures will offset that.”

This density, which causes the difference in altitude, is due to salinity: the Atlantic Ocean is saltier than the Pacific Ocean.

“The truth is that one might think that since the oceans are connected, they should be at the same level. But the Atlantic is lower, and that has to do with density. The Atlantic is denser than the Pacific, so the pressures will balance out at depth. The denser part It will push the less dense part a little further.

At this point, the mountain range that crosses America takes on a special role.

“The Andes, coastal mountains and Rocky Mountains in North America create a barrier that causes more rain in the Pacific Ocean and makes it less salty,” the expert says.

The lower salinity of the Pacific Ocean contributes to the difference in elevation.

“The latest studies show that rainfall is greater in the Pacific region. Salinity is a compensation between what evaporates and what falls, meaning water coming in and water coming out.”

Another factor that contributes to the difference in altitude is water temperature, which is another physical property that affects density.

Warm water is less dense than cold water, and temperature differences between oceans can lead to differences in sea level.

The Pacific Ocean has a slightly higher average temperature than the Atlantic Ocean, making it slightly less dense.

And let's remember: less dense means longer.

The topography of the sea floor also plays a role in the distribution of water and thus sea level.

In the deepest areas, ocean trenches – such as the Mariana Trench – are more than 11 kilometers deep.

Seamounts and mountain ranges act as obstacles to water movement.

“The ocean has many internal structures that fundamentally modify life in the sea. And so, these changes in sea level go through a lot of these oceanographic processes,” Buchan says.

This is how underwater mountain ranges, abyssal plains and ocean trenches can influence ocean circulation and generate variations in sea surface height.

The professor at the University of Concepcion says: “In Latin America specifically, we are witnessing another process related to atmospheric pressure and winds associated with the Humboldt Current, which is a cold current.”

“You can imagine that in the Pacific we have winds pushing water from Chile towards Indonesia. This also means that between Chile, Peru and Indonesia, on the other side, the sea surface height is different because of this wind process.

Is altitude affected by climate change and sea level rise?

“Satellite altimetry data shows that sea level rise is not uniform. For example, on the coast of Chile, sea level has practically not risen yet, unlike what is happening in Australia or on the other side of the Pacific Ocean.”

He says this is due to the fact that the oceans are warming in a heterogeneous manner.

In other words, when we talk about climate change, we cannot think that it will affect all regions in the same way. There are areas that will be more affected and others that will be less affected.”

How does it affect the Panama Canal?

America's most famous navigable waterway is also affected by the difference in altitude between the Pacific and the Atlantic Oceans, two oceans that it connects through its lock system that allows ships to navigate, uniting the two parts navigable at different levels.

If the canal were an open sea and had no locks, that is, if there was a direct connection in some way, a current would form that would flow from the less dense Pacific Ocean into the Atlantic Ocean.

The meeting would create a current that would make navigation dangerous because “the tides on either side would have opposite phases on each coast of Panama, so if there was a channel at sea level, there would be large tidal currents across it,” he explains. UK National Oceanographic Centre.

“The analogy, although imperfect because of many other factors, is to compare Panama to the Drake Passage, in the extreme south of Chile, which flows from west to east,” the service's website adds.

“Burds are needed on the Panama Canal because the canal extends over hills and uses mountain lakes. Therefore, barriers would be necessary even if sea level was the same on both sides.”