Ocean currents shape our world, from weather patterns to GDP. And somehow, we are managing to disrupt them.

Anengine, by definition, converts energy into movement, typically using solid metal parts driven by intense heat. But engines don’t need to be metal. The sun lights our Earth. As the elements soak it up, things heat up. The warm land and water heats the air above it, making it rise and pushing cooler air to slide beneath. Wind cruises over the ocean, pushing on water, and transferring energy back into the water as waves.

This is just one of the many routes energy navigates in the Earthly playground. The ocean is intricately linked to the atmosphere and land, working as a unified system where the ocean is the powerhouse engine. It turns sunlight into underwater currents, converting light and heat into movement while transporting life’s essentials: nutrients, oxygen, and trace metals. It sculpts our coastlines and regulates heat.

But this isn’t your average engine; it’s the ultimate one. And still, we call this planet Earth instead of planet Water.

The Nature of the Oceans

The skin of saltwater covering our planet, spanning 4 kilometers in depth and 12,740 kilometers in diameter, holds a compelling internal structure, defined by temperature and salinity, forming horizontal layers that evolve across the globe. Currents merge, water sinks and rises, and colossal sea-floor mountain ranges disrupt the flow.

Deep ocean basins feature three or four distinct layers, or water masses, with unique characteristics and histories, and typically remain independent.

The most notable internal boundary is the thermocline, marked by a rapid temperature change with depth, mostly used for the upper transition between warm, sunlit surface water and the cooler, darker depths below. This warm upper layer is the vital link between the sun’s power and the ocean engine fueled by that heat.

Ocean temperatures is a puzzle long known to seafarers. Unlike his contemporaries, Friedrich Wilhelm Heinrich Alexander von Humboldt, a German naturalist born in 1769, viewed nature as an intricate web of connections, not rigid categories. When he set sail in 1799 on a 5-year, 8000-km voyage of scientific discovery through Latin America, he aimed to collect data to assemble a unified theory of the natural world. In 1802, during a Pacific Ocean expedition, he noted a peculiar ocean current off Peru. This current defied expectations, with temperatures dropping to 16°C instead of the anticipated 28°C, creating distinct boundaries between warm and cold water.

It is not the most powerful or largest ocean current, nor is it one of the fundamental pulses that give rhythm to the life of our planet, like the famous Gulf Stream.

So, why is this strip of cold water along the west coast of South America, spanning 50 to 200 kilometers wide, so interesting? Its ecological, biological, and economic impact is essential not only for South America but also for the world. The Humboldt Current is a unique phenomenon based on paradoxes and exceptions. Its origin, operation, consequences, and even its name make it stand out. In simple terms, it is a powerful flow of cold water from Antarctica that flows along 5,000 kilometers of the Pacific coastline, fueling the oceanic food chain and supporting the world’s most productive industrial fishery since the mid-20th century, spanning from Chile to Peru. Humans have long recognized the value of the region’s exceptional natural resources. From their arrival on the continent at least 14,000 years ago to the guano collectors of the 19th century, and even to the Incas who settled in the mountains 200 kilometers from the coast, humans have been deeply influenced by this current.

A modern sea surface temperature map exposes a cool water tongue crawling up the western side of South America, affecting geopolitics, the Atacama desert, fishermen — and even pigs.

A Distinct Flavor for a Distinct Consumer

The immense submerged environment of the Humboldt Current is home to numerous species, including giant squids, over 50 species of sharks, sea lions, whales, and other cetaceans that traverse the globe.

The protagonist in this chilly current is the Peruvian anchoveta. Schools of anchoveta share cold waters with other fishes, sea lions, and seabirds becoming a moveable feast, a rare exception in the open sea. Delving into the biological chain reveals phytoplankton as the last source in the food chain. These microscopic plants aren’t just food. These are the most critical ocean inhabitants because they spend their time busily converting the sun’s energy into something the rest of the food chain can use. And in doing so, they not only contribute at least 50 percent of all oxygen to our atmosphere, they transfer 10 gigatons of CO2, an estimated 40% of all CO2 emissions into the deep ocean each year. To put things in perspective, this is equivalent to the amount of CO2 captured by 1.70 trillion trees — four Amazon forests’ worth — each year. So far, so good.

Once solar energy is harnessed, the food chain flourishes. However, the question arises: why are these phytoplankton, Earth’s tiniest powerhouses, thriving in the cold current instead of neighboring warm waters? This leads us to a profound consequence of the layered ocean.

Due to the movement of the Earth, there is pressure towards the depth of these particularly cold waters, which then tend to expand and spread towards the surface area. As a result of this phenomenon, the surface water layer tends to cool down, a basic element for the coastal ecosystem and the animal and plant species that live within it. It is because of this that the seas of Peru and Chile are, on average, 10 ° colder than those of neighboring states and the Pacific area.

Wondering why Peruvian anchovies aren’t a staple at your local fish shop?

Well, sea lions relish these small, oily fish, but humans find the taste “distinct” and “bold,” deterring widespread consumption.

Back in the 1950s, anchovies were largely overlooked by humans. Faced with abundant oceanic resources and wartime scarcity, people resorted to feeding the surplus to pigs. Post-World War II, countries like Great Britain encouraged self-sufficiency in food production, leading to the rise of “pig clubs” where groups collectively raised pigs making good use of household leftovers. But traditional leftovers wouldn’t meet industrial farm demands for scaling up pig production.

Meanwhile, in California, sardine fishermen were confronted with a collapse in the industry. The once-thriving canning factories now stood empty, as the sardine population had drastically declined due to excessive fishing. Despite protests from fishery biologists, around 500,000 tons of sardines were harvested each season from 1934 to 1946. By 1947, it all came to an end. Undeterred, Californian industrialists ventured to Peru, equipped with expertise and funds, to develop the anchoveta fishery.

Instead of canning anchovies for direct human consumption, the focus shifted to fishmeal production. Fishmeal, a concentrated powder derived from fish, particularly anchovies, contains a remarkable 50 to 70 percent protein by weight. Farmers, recognizing its potential, rapidly embraced fishmeal as a supplement for livestock feed. Between 1950 and 1973, global fish harvests tripled, yet human consumption remained stagnant. Fishmeal became a crucial element in modern industrial farming.

Britain, among other nations, avidly imported fishmeal, with half of it used as pig food by 1960. Industrial farming practices, coupled with antibiotics, allowed for faster and more economical pig production. By 1960, Peru emerged as the world’s top fishmeal producer, contributing to 40 percent of the global fish harvest by 1964.

When overfishing and environmental factors led to Peru’s fish harvest collapse in 1972, halting fishmeal supply, the price of British bacon doubled almost immediately. The anchovy’s journey, from the ocean to pigs, had a direct impact on people’s plates.

An Additional Natural Threat

The Humboldt Current is highly sensitive to the phenomenon of surface water heating up. El Niño events, occurring every 2–7 years, cause a significant decrease in phytoplankton productivity off Peru. This has a profound impact on the marine ecosystem, altering the environmental landscape and trophic chain. A study on the dynamics of productivity changes during El Niño reveals that the thermocline and nutricline deepen during the passage of coastal-trapped waves. While the depth of upwelling source waters remains unchanged, their nutrient content decreases dramatically. This, coupled with an increase in mixed layer depth, is the formula that affects the growth of phytoplankton.