In recent years, the idea of extracting gold from the ocean has captivated imaginations, but the reality remains complex and challenging. Although gold exists in seawater at trace levels, the concentrations are so minimal that traditional methods of extraction are not feasible.
Kelly Falkner and her team have been pivotal in providing a clearer understanding of gold levels in ocean water, establishing a reliable baseline for scientific measurements. Gold enters the ocean from various natural sources including rivers, aeolian dust, and hydrothermal vents on the seafloor. Furthermore, it often binds to particles or forms dissolved complexes with chloride, which keeps it distributed at exceedingly low concentrations.
A notable study has reported typical dissolved gold concentrations in the Atlantic and Northeast Pacific regions to be around 50 to 150 femtomoles per liter. At these levels, methods for measuring gold become critical; researchers employ trace metal clean bottles and process samples in controlled environments to prevent contamination from dust. Previous methods, such as solvent extraction and atomic absorption, have helped push detection limits into the nanogram range, but challenges remain.
The ocean holds only a few trillionths of a gram of gold per liter on average. In fact, a widely cited estimate suggests that the Atlantic and North Pacific contain about 1 gram of gold per 100 million metric tons of seawater. While this might seem significant given the vastness of the ocean, in practical terms, extracting such minuscule amounts with conventional methods proves nearly impossible.
Additionally, there are deposits of undissolved gold found on the seafloor, typically associated with sulfide minerals and crust formations, although these are located at depths of one to two miles. Explorers use remotely operated vehicles (ROVs) to map and sample these areas, but they rarely encounter gold nuggets directly.
The economics of extracting gold from seawater revolve around concentration, energy requirements, and selectivity. A comprehensive review of seawater mineral recovery techniques indicates that current methods are generally not viable for extracting trace metals like gold. Although there is ongoing research into engineering sophisticated sorbents for recovery, scaling these solutions to manage vast ocean flows at affordable costs remains a challenge. Proposals to integrate gold retrieval with desalination plants have not progressed beyond laboratory testing.
At the seafloor, gold deposits are similarly complicated, often buried deeply and intermingled with delicate vent ecosystems that need thorough exploration before any mining can be considered. Current research continues to investigate the quantity of gold stored in the ocean and its cycling through natural processes. Recent analyses estimate the global dissolved inventory of gold in the ocean to be about 14 million kilograms, with an estimated residence time of 220 years in seawater.
This research also indicates that only a small portion of gold introduced by hydrothermal vents remains nearby, with most dispersing into the deep ocean and settling with fine sediment. Future studies will focus on enhancing time-series data, refining particle chemistry, and developing advanced sensors.
The fascination with oceanic gold extraction often overlooks the realities of dilution and logistical hurdles. The science surrounding these efforts emphasizes the importance of thorough sampling, robust instruments, and an honest appraisal of uncertainties involved. As such, the narratives of vast riches lying in the ocean may not yield treasure but shine a light on the scientific process behind understanding our natural world.
This study is detailed in the journal Earth and Planetary Science Letters.
