By Janet Raloff
Researchers cruising the South Pacific between Tonga and Fiji study huge snails that, aided by an abundance of bacteria housed in their gills, feed off plumes of metal-rich compounds at active hydrothermal vents. Scientists working off the California coast use chemical-sniffing probes, robotically driven subs, and seafloor-tethered temperature sensors to watch flows of lava pave over a once-thriving ecosystem at hydrothermal vents several kilometers below the ocean’s surface. And in waters off Papua New Guinea, a mining company analyzes metal deposits around inactive, underwater volcanoes that contain, on average, 10 times as much copper as typical ores on land do.
These studies exemplify the breadth of research under way at one of Earth’s last great frontiers, the geologically active ocean bottom. Sites include hydrothermal vents on the 65,000-km-long ridge that meanders through all the world’s oceans and at deeply submerged volcanoes in the tropical west Pacific. Only 35 years ago, scientists didn’t know that geologically active sites existed underwater. Now, they have direct evidence of some 300 such spots and suspect that another 700 or so await discovery. The researchers are also uncovering signs of past geological activity at many sites.