20 million tonnes of gold lie beneath Earth's oceans. Can it be mined?

The world’s oceans are hiding a treasure so vast it almost sounds unreal.

Scientists say there could be around 20 million tonnes of gold dissolved in seawater, a stash that, on paper, could be worth more than $2 quadrillion.

But there’s a catch. The gold isn’t sitting in chunks or nuggets. It’s scattered in microscopic traces, so diluted that it may never be within our reach.

And yet, the question refuses to go away. With so much gold beneath the waves, could future technology ever make it possible to extract it? Or will it remain a glittering dream locked away by nature?

Here’s a closer look

But first, how did the gold get there?

The oceans didn’t magically fill up with gold. Instead, it’s the result of slow natural processes working over millions of years.

One major contributor is land erosion. As rain and rivers slowly break down rocks, tiny flecks of gold locked inside them get washed away and eventually carried into the sea.

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Another source lies in hydrothermal vents at the bottom of the ocean. These vents, usually found where tectonic plates meet, release scorching, mineral-rich fluids, sometimes carrying dissolved gold, into surrounding waters.

Even the wind has a role to play, blowing microscopic particles of gold dust across long distances until they finally settle in the oceans.

But here’s the catch: the concentration is incredibly small. Detecting it requires ultra-sensitive equipment.

According to research published in Earth and Planetary Science Letters and supported by polar scientist Kelly Falkner, gold in seawater is measured in “femtomoles per litre”, that’s just trillionths of a gram. In the Atlantic and Northeast Pacific, concentrations sit around 50 to 150 femtomoles per litre.

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Put simply, each litre of seawater contains only a few trillionths of a gram of gold. One estimate suggests you’d need a hundred million metric tonnes of seawater just to collect a single gram.

That sounds staggering when you think about the size of the ocean, but impossible when you picture trying to pull it out one bucket at a time.

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Why can’t we mine the gold in the oceans?

The first challenge is measurement. To detect such tiny amounts of gold, scientists must work in filtered labs with special trace-metal clean bottles to avoid even the smallest contamination. A speck of dust or residue on a container wall is enough to throw off results.

Before advanced tools like mass spectrometers were available, researchers relied on solvent extraction techniques to detect gold at nanogram levels. These older methods pushed the boundaries but were still nowhere near enough for extraction.

More recently, a 2018 study published in the Journal of the American Chemical Society proposed a sponge-like material that could absorb gold from seawater. While promising in theory, the technology is nowhere close to being scaled up profitably.

In short: the gold is there, but mining it simply doesn’t make economic sense.

What about the ocean floor?

Gold does exist in more concentrated forms on the ocean floor, locked inside sulfide deposits and mineral crusts. These deposits form near hydrothermal vents, where minerals accumulate over centuries.

But, they lie one to two miles deep, embedded in hard rock. While remotely operated vehicles (ROVs) can reach these depths, they usually come back with research samples, not bags of shiny nuggets.

Extracting gold from these deposits would not only be technically challenging but also raise serious environmental concerns.

Also read: Is Earth’s core leaking gold and other precious metals to the surface?

Questions that need to be answered

Despite the hurdles, scientists are still trying to understand the bigger picture. According to Earth.com, researchers continue to track how much gold flows through rivers, vents, and sediments, and how fast it cycles through the oceans.

One analysis estimated the total dissolved gold in the ocean at about 14 million kilograms, with a “residence time” of roughly 220 years. That means once gold enters the ocean system, it hangs around for centuries before settling.

Interestingly, studies show only a small fraction of the gold from hydrothermal vents stays near the source. Most of it drifts into the deep ocean, where it eventually settles with fine particles on the seafloor.

For researchers, the next steps are all about precision: collecting better time-series data, refining particle chemistry studies, and developing smarter sensors to track how these processes shift over time.

The dream of striking it rich by mining ocean gold may be a fantasy. But the science behind it isn’t a disappointment: it’s a story of patience,  sampling, and ever-improving technology that helps us understand how our planet really works.

With input from agencies