GabyResearchers at Hefei University of Technology in China have found a link between the amount of silver buried in marine sediments and human-driven climate change. They say global warming is causing vast silver reserves to be buried on the seafloor of the South China Sea, and similar processes could be happening across the world’s oceans. The amount of silver beneath the sea off Vietnam has surged since about 1850, the study’s authors reported. That timing lines up with the start of the Industrial Revolution, when humans began releasing greenhouse gases at scale, Live Science notes.
This is the first study to suggest a link between oceanic silver cycles and global warming, says lead author Lichuan Xu, an assistant professor of Earth sciences. He adds that warming could have unexpected effects on other trace elements, too.
How does silver concentrate and behave underwater? Like other elements, silver starts on land and reaches the ocean mainly through weathering: rain washes elements from rocks into rivers. Some ocean regions get enriched with silver from river inflow, atmospheric dust, human emissions, and hydrothermal vents. In its ionic form (Ag+), silver is toxic to marine life. But little is known about how silver interacts with broader ocean ecosystems, Xu says.
To learn more about how silver behaves in marine environments, Xu and his colleagues analyzed sediment cores from an upwelling zone in Vietnam, located in the eastern part of the South China Sea. Upwelling zones are coastal areas where cold water rises from the ocean floor, bringing nutrients that support surface ecosystems.
The researchers split the sediment core from the upwelling zone into two sections. Silver concentration fell from the base of the core—dated to around 1200 B.C.—up to about 7 centimeters below the top. But the uppermost section showed a very different pattern. “The burial of silver over the last 3,200 years shows a sharp increase around 1850,” the authors write. That timing lines up with a large rise in CO2 emissions into the atmosphere.
Silver concentrations in upwelling zones are typically high. The researchers say silver levels off Vietnam were naturally elevated and comparable to measurements from upwelling areas off Canada, Mexico, Peru, and Chile. But those earlier studies did not connect high silver concentrations to global warming.
Warming raises water temperatures and strengthens coastal winds, which can intensify upwelling. That brings more nutrients to the surface, fueling algal blooms that support the food chain. Higher concentrations of dissolved silver in these regions mean organisms may absorb more of it. When those organisms die and sink, they carry silver down to the seafloor.
Silver enters sediments with organic matter, Xu explains. Deep-water upwellings are intensifying with global warming, and the authors believe that silver content in sediments across these areas is increasing. High levels of silver in sediments can leach back into seawater, he warns. If that happens on a global scale, it could poison ocean ecosystems. If silver doesn’t leach back into water, the authors say it will eventually make its way back to land. “Nothing is truly lost; it just gets moved around,” they write.
The study appears in the journal Geophysical Research Letters.
