How Do Oceans Circulate? Crash Course Geography #9

Summary

The North Pacific Garbage Patch, a massive collection of trash spanning approximately 700,000 km2, illustrates the impact of ocean currents on global pollution. Driven by wind and differences in density and pressure, these currents transport debris like plastic across oceans, contributing to gyres where trash accumulates. The video explores how these currents, influenced by the Coriolis Effect and landmasses, shape marine ecosystems and affect global trade, underscoring the interconnectedness of pollution and the need for collective responsibility in addressing it.

Takeaways

• 🌊 The North Pacific Garbage Patch is a massive collection of trash vortices in the Pacific Ocean, mostly made of microplastics.
• 🌍 It is one of five large trash patches circulating in the world’s oceans, with plastic pollution visible even on beaches.
• 🌪️ Ocean currents, similar to wind patterns, are predictable flows of energy influenced by density and pressure differences.
• 🏝️ The size and movement of the North Pacific Garbage Patch are constantly changing, making it difficult to define its exact dimensions.
• 🌀 Ocean gyres, like the North Pacific Gyre, move trash across vast distances, powered by ocean currents and wind.
• 🧪 Water density is affected by both temperature and salinity, with warm water expanding and saltier water being denser.
• 🐟 Deep ocean currents play a crucial role in circulating nutrients and oxygen, supporting marine life and fisheries worldwide.
• 🚢 Modern marine debris is mostly plastic, with over 8 million metric tons of plastic waste polluting the oceans annually.
• 🚛 Shipping containers lost at sea contribute to ocean pollution, and international waters lack clear ownership for cleanup responsibility.
• 🌍 The interconnectedness of global ocean currents highlights how marine debris and pollution impact environments across the globe.

Q & A

What is the North Pacific Garbage Patch and how is it formed?

The North Pacific Garbage Patch is a massive collection of human-made trash, mostly composed of microplastics, chemical sludge, and wood pulp, circulating in the Pacific Ocean. It is formed by ocean currents that gather debris from various parts of the world into large areas known as gyres.

Why is it difficult to define the size of the North Pacific Garbage Patch?

The size is difficult to define because the Garbage Patch is not a solid mass of trash but rather a 'soup' of tiny microplastics that constantly move with ocean currents. Some scientists estimate it covers around 700,000 km², roughly the size of Texas.

How do ocean currents influence the movement of trash around the globe?

Ocean currents, driven by wind patterns and differences in water density, act like highways that move water and debris around the world. The trash can travel vast distances across oceans, getting caught in gyres and sometimes washing up on distant shores.

What is the role of the Coriolis effect in shaping ocean currents?

The Coriolis effect, caused by the Earth's rotation, deflects the movement of ocean currents, particularly as they move north or south. This creates curved paths, influencing the direction and flow of currents, which is stronger near the poles and weaker at the equator.

What are gyres, and how do they contribute to ocean circulation?

Gyres are large systems of circular ocean currents formed by global wind patterns and forces from Earth's rotation. They help circulate warm and cold water around the globe, moving marine debris, nutrients, and sometimes living organisms like fish or eels.

How do surface currents affect global climate?

Surface currents transport warm water from the equator towards the poles and cold water from the poles toward the equator. This movement regulates regional air temperatures, moderates climates, and plays a critical role in distributing heat across the planet.

What is the difference between surface currents and deep currents in the ocean?

Surface currents move horizontally across the top layer of the ocean, primarily driven by wind patterns. Deep currents, on the other hand, move more slowly at lower depths, driven by differences in water temperature and salinity, and play a key role in nutrient circulation.

How do deep ocean currents contribute to marine ecosystems?

Deep ocean currents are responsible for upwelling, which brings nutrient-rich water from the ocean floor to the surface. These nutrients support marine ecosystems and fisheries, particularly near coastal areas, which are vital for global fish harvests.

Why are plastic particles and other marine debris so persistent in the ocean?

Marine debris, especially plastics, do not biodegrade like organic materials. Instead, they are broken down by wind, waves, and sunlight into microplastics, which can persist for years in the ocean, often getting trapped in gyres and accumulating in garbage patches.

How does human activity contribute to marine pollution, and what challenges exist in addressing it?

Human activity, such as improper waste disposal, industrial pollution, and accidents like shipping container spills, contribute to marine pollution. Addressing this issue is challenging because trash in the oceans often crosses international boundaries and cleaning international waters is difficult to coordinate.

Outlines

00:00

🌊 Overview of the North Pacific Garbage Patch

The North Pacific Garbage Patch is the world's largest human-made trash dump, consisting of a series of trash vortices. It is not a solid mass but rather a soup of microplastics spread across the ocean, roughly the size of Texas. This is one of five major ocean trash collections globally, linked to human activity and ocean currents. Ocean currents and wind patterns drive plastic pollution from inland areas to beaches worldwide, connecting everyone to this issue, regardless of proximity to the coast. Hosted by Alizé Carrère, this episode of Crash Course Geography discusses how ocean currents transport trash across vast distances, illustrating the global connectivity of ocean pollution.

05:01

🌬️ The Role of Wind and Ocean Currents

Wind is a key driver in the movement of ocean water. Ocean currents, much like winds, move in predictable patterns due to differences in temperature and pressure, which are influenced by the amount of solar energy received. Warm water, being less dense, rises and forms surface 'hills' in the ocean, while cold or salty water, being denser, sinks, creating depressions. These movements are guided by pressure gradients, propelling water globally. Wind transfers energy to water through friction, which helps generate surface currents. The Coriolis effect further curves these currents as they interact with landmasses and the Earth's rotation, forming complex patterns of movement.

10:04

🏞️ Gyres and Global Ocean Circulation

Ocean gyres, created by wind and the Coriolis effect, play a major role in circulating water around the world. These massive systems are responsible for moving warm and cold water, shaping climate and distributing trash, including microplastics. In the North Pacific Gyre, for example, ocean currents converge to trap floating debris, forming the North Pacific Garbage Patch. The journey of a water bottle thrown into the ocean is used as a metaphor for the movement of debris through these ocean systems, highlighting how trash can travel long distances across the globe.

🌍 Deep Ocean Currents and Thermohaline Circulation

Beyond surface currents, deep ocean currents move water horizontally and vertically, driven by differences in temperature and salinity. This process, known as thermohaline circulation, transports nutrients, heat, and oxygen around the globe. Deep currents are slower but crucial for sustaining marine life, particularly near nutrient-rich upwellings that support large fisheries. These upwellings only cover 1% of the ocean's surface but account for a significant portion of global fish production, essential to the livelihoods of a billion people worldwide. The deep ocean's 'conveyor belt' connects the poles to the equator, playing a vital role in regulating marine ecosystems.

🛳️ The Impact of Shipping and Marine Debris

Modern marine debris, largely made of plastic, is a byproduct of global trade and shipping. Each day, 50,000 cargo ships transport goods across the oceans, contributing to both air and ocean pollution. These ships often lose containers due to storms, adding large objects like LEGO pieces and Garfield phones to the ocean's trash. While ocean currents carry much of this debris across the globe, smaller local currents can deposit it on shores, revealing a culture of material waste. The extensive movement of goods across oceans is critical to global trade, but it also highlights the environmental cost of our reliance on shipping.

🌪️ Global Ocean Pollution and Responsibility

Plastic pollution in the oceans is a global issue that crosses political boundaries, with 8 million metric tons of plastic debris present worldwide. This pollution underscores how interconnected we are through air and water circulation. Marine ecosystems, trade, and local economies rely on predictable ocean currents, but the growing amount of marine debris poses a significant environmental challenge. The video ends with a reflection on the difficulty of cleaning international waters and the need to balance economic activities with environmental protection, leaving viewers with the question of who is responsible for addressing this global issue.

Keywords

💡North Pacific Garbage Patch

The North Pacific Garbage Patch is a massive collection of marine debris, mainly microplastics, floating in the Pacific Ocean. It is not a solid 'island' of trash but rather a swirling mass of tiny particles and some larger items, forming a kind of 'soup' in the water. The video highlights this area as one of the largest human-made trash accumulations, where ocean currents trap waste, demonstrating the global scale of plastic pollution.

💡Microplastics

Microplastics are tiny plastic particles that result from the breakdown of larger plastic objects due to exposure to sunlight, wind, and waves. These microscopic pieces are a significant component of ocean pollution, often invisible to the naked eye but pervasive in marine ecosystems. The video discusses how trash like water bottles disintegrates into microplastics over time, contributing to pollution in the North Pacific Garbage Patch and other ocean gyres.

💡Ocean Currents

Ocean currents are continuous, directed movements of seawater driven by various forces such as wind, the Earth's rotation, and differences in water density due to temperature and salinity. The video explains how ocean currents, like the Equatorial Current and Kuroshio Current, transport debris and energy across the globe, connecting ecosystems and contributing to the spread of pollution, such as plastics in garbage patches.

💡Gyres

Gyres are large systems of circulating ocean currents that move in a consistent direction. They are critical in the formation of garbage patches, like the North Pacific Garbage Patch, by trapping debris in their circular flow. The video describes five major gyres worldwide, including the North Pacific Gyre, which is made up of multiple currents working together to move water and pollutants across vast oceanic regions.

💡Coriolis Effect

The Coriolis Effect is the deflection of moving objects, like air or water, due to the Earth's rotation. This effect causes ocean currents to curve rather than move in straight lines, influencing the patterns of gyres. The video explains how the Coriolis Effect bends ocean currents and affects their direction, contributing to the formation and movement of ocean gyres and, consequently, the global distribution of marine debris.

💡Salinity

Salinity refers to the concentration of salt in seawater, which affects water density. In the video, it is explained how saltier water is denser than less salty water, which plays a role in ocean circulation. Changes in temperature and salinity drive both surface and deep ocean currents, which are responsible for moving debris and nutrients around the globe.

💡Thermohaline Circulation

Thermohaline circulation is the global conveyor belt of ocean currents driven by differences in temperature and salinity, which cause variations in water density. This deep-sea current system is essential for moving nutrients, oxygen, and marine debris throughout the world's oceans. The video highlights how these slow-moving currents help distribute essential elements like nutrients for marine life and move pollutants like plastic deep into the ocean.

💡Nonpoint Source Pollution

Nonpoint source pollution refers to pollution that cannot be traced to a single source, such as runoff from land or diffuse plastic debris in the ocean. The video mentions how much of the plastic in the oceans originates from unknown sources, adding to the complexity of addressing marine pollution. This term underscores the global and often uncontrolled nature of plastic waste entering the marine environment.

💡Upwelling

Upwelling is the process by which deep, nutrient-rich water rises to the surface, providing vital resources for marine ecosystems. The video discusses how upwelling areas, though covering only 1% of Earth's oceans, contribute to 50% of the global fish harvest by supporting highly productive marine environments. These currents also illustrate the important role of deep ocean circulation in sustaining life and impacting human economies.

💡Shipping Container Pollution

Shipping container pollution refers to the debris created when containers are lost from cargo ships, often due to storms or accidents. The video illustrates how large items like LEGO dragons or rubber ducks can end up in the ocean after containers fall into the sea. This type of pollution emphasizes how modern global trade contributes to marine debris, with thousands of containers lost each year, adding to the overall problem of ocean pollution.

Highlights

The North Pacific Garbage Patch is the largest human trash dump in the world, consisting of a series of trash vortices spread across the Pacific Ocean.

The patch is not a solid island of trash but rather a soup of microplastics, making its size difficult to define, though some scientists estimate it to be around 700,000 km², the size of Texas.

There are five giant garbage patches circulating in oceans worldwide, all driven by ocean currents and global winds.

Plastic pollution is found on beaches globally, with tiny, almost invisible microplastics present due to trash movement from inland to the oceans and through currents.

The circulation of ocean currents, similar to wind patterns, moves energy and trash around the globe through predictable currents driven by differences in water density and pressure.

Surface ocean currents are heavily influenced by wind friction, transferring energy from air to water, forming large-scale circulation patterns called gyres.

The Coriolis effect, caused by Earth's rotation, curves ocean currents, bending them into circular patterns, especially in higher latitudes.

The North Pacific Gyre is a combination of four major ocean currents that trap floating debris, including plastics, leading to the creation of the North Pacific Garbage Patch.

Ocean currents do more than transport debris; they regulate global climate by moving warm water poleward and cold water toward the equator.

Deep ocean currents move slower than surface currents, transporting nutrients from the ocean floor to surface waters, crucial for marine life and global fisheries.

Upwelling, driven by deep currents, brings nutrient-rich water to the surface, supporting ecosystems that produce 50% of the global fish harvest.

Global ocean currents not only move marine life but also carry human trash, contributing to widespread pollution, especially plastics that degrade into microplastics.

Shipping containers lost at sea are a significant source of ocean debris, contributing to pollution as global trade continues to rely on container ships for 90% of goods.

The global ocean circulation system, driven by both surface and deep currents, is essential for the movement of goods, nutrients, and energy, connecting ecosystems and economies.

Plastic debris in the oceans reflects humanity’s environmental impact, with questions about responsibility for cleaning international waters remaining unresolved.

Transcripts

Welcome to the North Pacific Garbage Patch, the largest human trash dump in the world.

Spreading across the Pacific Ocean, the North Pacific Garbage Patch is really more of a

series of trash vortices and is the top vacation destination for plastic, chemical sludge,

and wood pulp. 

Defining its size is difficult because it’s always moving and it’s mostly a soup of

tiny microplastics, not an island of grocery bags and drinking straws. But some scientists

estimate it’s approximately 700,000 km2, which is roughly the size of Texas.,

Actually, it’s one of five giant collections of trash circulating in oceans all over the Earth. 

If you’ve spent time on beaches, you might’ve noticed plastic trash like water bottles and

toys, but there's so much almost invisible junk too, like small beads or tiny slivers.

Each beach around the world has this plastic pollution because of how trash moves from

inland to the ocean, and then gets caught in ocean currents. 

Whether you live on a coast or not, everyone is connected to the global ocean currents

circulating tremendous amounts of energy…and trash. 

I’m Alizé Carrère and this is Crash Course Geography.

Intro

Somehow trash can show up on a beach in California from a pod of trash 2500 nautical miles away

east of Hawaii. That’s so far for one speck of plastic or even a whole water bottle [-- with

or without the secret message --] to travel. To get there, it all starts with the wind. 

In our last episode, we explored how the horizontal movement of air, called wind, moves in predictable

directions and creates the general patterns for global circulation. In the oceans, we

call the horizontal movement of water an ocean current. 

Like the winds, ocean currents are basically rivers of energy moving in a persistent and

predictable direction. And also like the winds, ocean currents are driven by differences in

density and pressure. 

In the air, density and pressure changes come from differences in the amount of insolation,

or incoming solar radiation, that different parts of the atmosphere receive. 

And ocean water is heated by insolation too. Because of how much direct sunlight it gets,

water closer to the equator absorbs more heat energy than water at higher latitudes. 

This creates density differences within the ocean, because -- just like air -- warm water

is less dense than cold water. Basically when heated, molecules like to spread out. Water

density is also affected by salinity, or the salt content of the water. Saltier water is

more dense than less salty water, because there are more molecules of salt and water

hanging around.

Warmer water in the ocean expands just like air, but because it can’t expand sideways

-- because ya know, there’s already water there -- it expands up, elevating the surface

just slightly, like a hill. And colder or saltier water contracts, lowering the surface

into a depression. So the ocean’s surface isn’t perfectly flat. It contains sea surface

height anomalies. 

A “hill” of water exerts extra pressure compared to a dip in the sea surface height.

And in general, whatever’s in a high pressure area -- whether it’s air or water or a student

in a stressful class -- wants to move to the low pressure area. So these pressure gradients

force the water to flow around the globe.

Technically it's all the same water, but separate currents are defined because they consistently

move in the same way, kind of like different highways of water.

There are actually at least 30 major named surface currents and dozens more smaller currents

transporting ocean water around the globe. So if our trash found its way to the right

spot, it could travel the world!

We can draw lots of comparisons between ocean currents and wind patterns, but surface currents

are also driven by strong and steady streams of wind. Energy is transferred from the winds

to the water through friction as air blows across the surface.

For example, the winds that result from subtropical high pressure areas around 30 degrees latitude

also help create the ocean currents that circulate there in patterns called gyres. 

But even though ocean currents generally follow the winds, the two aren’t mirror images.

Ocean currents come up against huge roadblocks that air blows right over: continents and

large land masses. 

These roadblocks give currents irregular shapes, especially in places like the Indian Ocean,

the Arctic Ocean, and the Northern Atlantic Ocean where there’s lots of land. 

Currents are also curved by the Coriolis Effect, like all fluids on the Earth’s surface.

Remember the Earth is rotating fastest at the equator and slower as we move towards

the poles. So if something that’s not directly connected to land moves north or south, the

change in momentum causes its path to bend. 

The Coriolis effect can actually deflect some surface currents, depending on where they

are on the globe. Like, as currents move away from the equator, the Coriolis effect gets

stronger because the Earth’s rotational speed rapidly slows down, and can break up

currents into chains of lots of circular vortices, or eddies. These get smaller the closer you

are to the poles as the Coriolis effect bends the currents ever more tightly. 

Then as the Earth rotates faster as we move towards the equator, the Coriolis effect gets

weakest until it’s basically nonexistent exactly at the equator. So equatorial currents

aren’t deflected right or left -- water can simply flow in a straight direction pushed

by the winds. 

So if we look at the circulation map, most of the surface currents making up gyers don’t

cross the equator but flow along it horizontally. Then it’s the combined forces of winds and

the Coriolis effect that causes gyres to flow in a clockwise direction in the Northern Hemisphere

and a counterclockwise direction in the Southern Hemisphere. 

But let’s go back to the idea that ocean currents not only run into stuff like land,

they can also carry more stuff than wind. Maybe they're a highway for eel migration,

or they play a role in a water bottle's journey from a store shelf to the North Pacific Garbage Patch.

At some point, this bottle got snagged in the North Pacific Gyre, which is really four

currents that follow how the air moves around the northern subtropical high pressure area.

To imagine its journey, let’s go to the Thought Bubble.

Let's say our water bottle fell into a municipal storm drain in Hawaii that got flushed into

the Pacific Ocean. 

Starting at the equator, the trade winds drive water west in a flow called the Equatorial Current.

This carries our water bottle to the eastern coastline of Asia, where warm waters pile

up against the land.

So the warm, energy-rich waters are deflected toward the North Pole, pushed by both pressure

gradients and the Coriolis effect that balance each other out.

They flow into the Kuroshio Current moving north along the Asian East Coast, where our

bottle could wave at the Philippines and Japan...you know, if water bottles had arms.

As it reaches the latitude of the westerly winds around 35 degrees north, the current

begins to wobble more, and along with our bottle, is pushed eastward and separates from the coast.

This forms the North Pacific Current, bringing warm waters to the southern coast of Alaska. 

And then, land ho! Eventually our bottle encounters the West Coast of North America and is deflected

back towards the equator, moving from British Columbia, Canada, to the Baja Peninsula in Mexico.

This California Current is cold, having released the warmth that the water was holding in the

Equatorial and Kuroshio currents. 

If the bottle manages to stay in the gyre, it could float on through those warm and cold

currents for years, traveling through clear moonlit nights and rough typhoons. 

Because our bottle is a processed plastic, bacteria don't eat away at it.

But wind, waves, and sunlight have broken it down into microscopic particles, so all

that's left is a bead that ends up floating in the North Pacific Garbage Patch. 

Thanks, Thought Bubble. Wind-current interactions are actually much more complicated than just

winds “pushing” water around, and it’s an area oceanographers are still trying to understand.

For geographers, we’re concerned with how stuff gets moved around the globe. There are

actually five major gyres in the world, including this North Pacific Gyre, each with its own garbage patch.

And they all follow similar patterns with warm currents bringing warmth and humidity

to the continental east coasts, and cold currents moderating temperatures and having a drying

effect on the west coasts. 

Ocean circulation in the Southern Hemisphere is similar except that the gyres flow in a

counterclockwise direction. And because there’s very little land poleward of 40 degrees south,

the Antarctic Circumpolar Current or West Wind Drift circles around Antarctica as a

cold current almost without interruption or directly interacting with the warm equatorial waters.

Surface currents generally move warm waters poleward and cold waters towards the equator,

so they're important regional air temperature regulators in addition to moving anything

that happens to be in the ocean, from schools of fish to bits of plastic! 

But surface currents don't make up all of the horizontal motion of the ocean. To see

the rest, we have to go deep into the ocean.  Deep currents travel at slower speeds beneath

the surface currents. They move ocean waters both horizontally across the floors of the

world’s oceans, but also vertically from the ocean floor to the bottom of surface currents

as part of Earth’s thermohaline circulation. 

Just like surface currents, deep currents flow from high pressure to low pressure. Even

at these crushing depths, slight pressure and density differences are also caused by

temperature and salinity changes.

For example, the more salt content the surface water has, the more dense it is, the more

likely it will sink as it reaches the poles. In some places, that water will sink up to

2000 meters to where deep currents flow. A complete circuit of a deep current may take

up to 1000 years. 

Even still, deep currents are critical to the movement of nutrients around the world.

Many fisheries, for example, depend on cyclical upwelling of nutrient-rich water moving from

deep currents into local surface currents. 

While nutrients released through decomposition near the ocean floor are pulled up by upwelling,

oxygen cycles down from the surface to the deep, which keeps those decomposers and other

deep-sea organisms supplied with oxygen for respiration.

So the broad global circulation of deep currents is like a vast conveyor belt of ocean water

that brings warmth from the equator to the poles, nutrients from the floor to the surface,

and oxygen from the surface to the floor. 

Marine habitats near upwellings only cover about 1% of Earth’s oceans, but account

for up to 50% of the global fish harvest. At least a billion people rely on fish for

their primary protein, so deep ocean circulation not only moves energy around the globe, but

also helps create the conditions that feed a large part of the world. 

Higher up, dominant winds and surface currents have helped move people around the globe for

thousands of years. 

With the movement of ships, has come the movement of people and the things they deem most important.

We can understand the material culture of a people by the marine debris they create. 

Some of that trash will get swept into regional surface currents like gyres, but some will

get caught by smaller local currents and wash up on shore without traveling the world.

Like there have been outbreaks of whole toys washing up on beaches, from rubber ducks to

LEGO dragons to Garfield phones. What do all these things have in common? Well, like you've

probably intuited, marine debris in the 21st century is mostly plastic. 

There are 8 million metric tons of plastic bits and debris we don’t know the origin

of, or nonpoint source pollution, that’s estimated to be in the oceans, but there’s

also bigger garbage out there too. 

Take that whole LEGO dragon -- it didn't travel far. It came from a wrecked shipping container

that fell into the ocean after a huge once-in-a-100-years wave hit the cargo ship that was carrying it.

In fact, there are thousands of shipping containers each year that fall off cargo ships due to

rough weather or other mishaps. This map shows the movement of the 50,000 ships each day

moving goods around the globe.

Some estimates say 90% of global trade involves container ships crossing the oceans. 

But as ships move, they’re emitting air pollution that rides on global air circulation

currents through the atmosphere, or dropping stuff that contributes to ocean pollution. 

These types of pollution can’t be linked to a particular ship because air and water

cross political boundaries. 

In fact, those plastic beads and dragons on the beach represent how we're all connected

by the global circulation of air and water… and how garbage patches won’t clean themselves. 

Our global economies depend on the circulation of goods moved by ships, and local economies

depend on the circulation of nutrients that create rich fisheries, all of which leverage

the dependability of ocean currents. 

So who is responsible for cleaning international waters, and how do we balance our societal

needs with protecting the planet? There aren’t easy answers, and there might be rough seas

ahead. In fact, I see some clouds on the horizon... 

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