How Much Gold Is in the Ocean?

Many have tried and failed to earn a living by taking gold from the sea

In 1872, British chemist Edward Sonstadt published a report declaring the existence of gold in seawater. Since then, Sonstadt's discovery has inspired many, from well-intentioned scientists to con artists and swindlers, to find a way to extract it.

Quantifying the Ocean's Riches

Numerous researchers have sought to quantify the amount of gold in the ocean. The exact amount is difficult to pinpoint because gold exists in seawater at very dilute concentrations (estimated to be on the order of parts per trillion, or one part gold per trillion parts water).

A study published in measured the concentration of gold in samples taken from the Pacific Ocean, and found that they were about 0.03 parts per trillion. Older studies reported a concentration of about 1 part per trillion for seawater, about 100 times more than other, more recent reports.

Some of these discrepancies may be attributed to the presence of contamination in the samples collected as well as the limitations of technology, which in past studies may not have been sensitive enough to accurately detect the quantity of gold.

Calculating the Amount of Gold

According to the , there are about 333 million cubic miles of water in the ocean. One cubic mile is equivalent to 4.17 * 109 cubic meters. Using this conversion, we can determine that there are about 1.39 * 1018 cubic meters of ocean water. The density of water is 1000 kilograms per cubic meter, so there are 1.39 * 1021 kilograms of water in the ocean.

If we assume that 1) the concentration of gold in the ocean is 1 part per trillion, 2) this concentration of gold holds for all ocean water, and 3) parts per trillion corresponds to mass, then we can calculate an approximate amount of gold in the ocean using the following method:

• One part per trillion corresponds to one trillionth of the whole, or 1/1012.
• Thus, to find out how much gold there is in the ocean, we must divide the amount of water in the ocean, 1.39 * 1021 kilograms as calculated above, by 1012.
• This calculation results in 1.39 * 109 kilograms of gold in the ocean.
• Using the conversion 1 kilogram = 0.0011 tons, we reach the conclusion that there are about 1.5 million tons of gold in the ocean (assuming a concentration of 1 part per trillion).
• If we apply the same calculation to the concentration of gold found in the more recent study, 0.03 parts per trillion, we reach the conclusion that there are 45 thousand tons of gold in the ocean.

Measuring the Amount of Gold in Seawater

Because gold is present in such low quantities and is included with many other components from the surrounding environment, samples taken from the ocean must be processed before they can be adequately analyzed.

Preconcentration describes the process of concentrating the trace amounts of gold in a sample so that the resulting concentration lies in the optimal range for most analytical methods. Even with the most sensitive techniques, however, preconcentration may still yield more precise results. These methods include:

• Removing water through evaporation, or by freezing water and then sublimating the resulting ice. Removing water from seawater, however, leaves large quantities of salts like sodium and chlorine behind, which must be separated from the concentrate before further analysis.
• Solvent extraction, a technique in which multiple components in a sample are separated based on how soluble they are in different solvents, like water versus an organic solvent. For this, gold can be converted to a form that is more soluble in one of the solvents.
• Adsorption, a technique in which chemicals adhere to a surface like activated carbon. For this process, the surface can be chemically modified so that gold can selectively adhere to it.
• Precipitating the gold out of solution by reacting it with other compounds. This may require additional processing steps that remove other elements in the gold-containing solid.

The gold can also be further separated from other elements or materials that may be present in the samples. Some methods for achieving separation are filtration and centrifugation. After the preconcentration and separation steps, the quantity of gold can be measured using techniques that are designed to measure very low concentrations, which include:

• Atomic absorption spectroscopy, which measures the amount of energy a sample absorbs at specific wavelengths. Each atom, including gold, absorbs energy at a very specific set of wavelengths. The measured energy can then be correlated to concentration by comparing the results to a known sample, or reference.
• Inductively coupled plasma mass spectrometry, a technique in which atoms are first converted to ions, and then sorted depending on their mass. The signals corresponding to these different ions can be correlated to concentration by correlating them to a known reference.

Key Takeaways

• Gold exists in seawater, but at very dilute concentrations – estimated, in more recent times, to be on the order of parts per trillion. Because this concentration is so low, it is difficult to pinpoint exactly how much gold is in the ocean.
• Even if there is an abundance of gold in the ocean, the cost to extract the gold from the sea would most likely outweigh the value of the gold collected.
• Researchers have measured these small concentrations of gold with techniques that are capable of measuring very low concentrations.
• Measurements often require that the gold be preconcentrated in some way and separated from other components in a seawater sample, to minimize the effects of sample contamination and allow for more precise measurements.

References

• Falkner, K., and Edmond, J. “Gold in seawater.” 1990. Earth and Planetary Science Letters, vol. 98, pp. 208-221.
• Joyner, T., Healy, M., Chakravarti, D., and Koyanagi, T. 1967. Environmental Science and Technology, vol. 1, no. 5, pp. 417-424.
• Koide, M., Hodge, V., Goldberg, E., and Bertine, K. Applied Geochemistry, vol. 3, no. 3, pp. 237-241.
• McHugh, J. Journal of Geochemical Exploration. 1988, vol. 30, no. 1-3, pp. 85-94.
• National Ocean Service.
• National Ocean Service.
• Pyrzynska, K. 2005. Spectrochimica Acta Part B: Atomic Spectroscopy, vol. 60, no. 9-10, pp. 1316-1322.
• Veronese, K. Gizmodo.