Deep-sea hydrothermal vents more abundant than thought

The deep, dark ocean bottom teems with far more oases of life than once thought.

Searching along the sunless seafloor where tectonic plates pull apart, regions known as spreading ridges, researchers discovered that heat-spewing hydrothermal vents are at least three to six times as abundant as previously assumed. The finding also significantly boosts the likely number of marine ecosystems huddled around vents, the researchers report in the Sept. 1 Earth and Planetary Science Letters.

“The common knowledge of vent field distribution — that they’re typically separated by tens or hundreds of kilometers — was not telling the whole story,” says study coauthor Edward Baker, an oceanographer at the University of Washington in Seattle. In reality, vents are spaced around three to 20 kilometers apart along spreading ridges, Baker and colleagues found.

Hydrothermal vents are underwater hot springs. Near tectonic plate boundaries, seawater seeps through the ocean floor and gets heated by molten rock. The hot water then erupts back into the ocean, bringing dissolved minerals such as iron along for the ride. The expunged minerals build smokestack-like towers that host bizarre ecosystems of giant tube worms, eyeless shrimps and ghostly white crabs that thrive in the hot, nutrient-rich water (SN: 7/25/15, p. 4).

Discovery of additional vents resolves a long-standing mystery about how vent-dwelling sea life spreads, says Duke University oceanographer Cindy van Dover, who was not involved in the work. Critters that call vents home aren’t very mobile and their offspring can’t travel very far, yet scientists find genetically related communities far apart (SN Online: 2/26/10). The new results show that “there are even more stepping stones than we thought,” she says. “This helps us understand the resilience of these communities and how they relocate.”

Vent hunters typically search for visual signs of the smokelike streams of particles belched by many hydrothermal vents. Puffs of these smoke signals can extend for tens of kilometers horizontally, though, making it difficult to discern between individual vents in closely grouped clusters. Also, many low-temperature vents emit few particles, making the vents difficult to spot.

Using a special new sensor, Baker and colleagues scanned for short-lived chemicals that all vents expel, such as unoxidized iron and sulfur. The researchers hunted for slight changes in the electrical properties of seawater caused by the vent-emitted chemicals. This technique allows the researchers to detect low-smoke vents. Since the chemicals don’t extend as far as the smokelike particle plumes, the researchers can also discern between vents about a kilometer or more apart.

Over the course of several research trips, the researchers scoured 1,470 kilometers of the eastern Pacific Ocean seafloor where tectonic plates separate. The new sensor, towed by a ship, drifted within a few hundred meters of the seafloor. In total, 184 distinct vent sites were found, far more than expected based on previous vent inventories. Around a quarter of the sites were low-temperature, particle-poor vents overlooked in previous studies. The finding could also apply to other spreading ridges, such as those in the Atlantic and Indian oceans.

“They’re not all big, they’re not all the iconic black smokers, but they’re places that likely support ecosystems, so there’s way more places on the seafloor where animals can survive,” Baker says. The impact of the hydrothermal vents on life extends beyond the ocean floor, Baker adds. Iron released from the vents can travel thousands of kilometers and have a global impact on availability of the nutrient.