Black Smokers


Black smokers are hydrothermal vents on the sea floor where hot water erupts into the freezing waters of the deep ocean. The hot water is less dense than the surrounding deep ocean water so it rises in the water column, expands and drifts in the water current which makes it resemble smoke coming out of a smokestack. The black color comes from the precipitation of minerals when the hot hydrothermal fluid (340 degrees C) mixes with the cold sea water (1-2 degrees C). Black smokers are usually the hottest vents, while others may appear white and others show no color at all due to the type of minerals precipitating out of the water. Colorless smokers lack color because the temperature difference between hot vent water and cold sea water is not extreme enough to cause the minerals to precipitate.

Hydrothermal vents are found along the mid-ocean ridges. In the ridge zones the crust is separating and magma rises closer to the top of the crust. Hydrothermal vents have several distinct zones. In the recharge zone, sea water that seeps into the crust is slowly heated by the magma that has warmed the crust. As the water heats and moves through the crust, it reacts with the rock and changes its chemical components. The water seeps through the rock and is hottest in the high temperature reaction zone. The hot water rises through the crust in the upflow zone, and is expelled back into the water column through the vents. Sulfides and sulfates of minerals precipitate out of the water column as the hot water and cold water collide. As the precipitates settle they accumulate forming chimneys that rise from the sea floor tens of meters.

The chimneys are not isolated geological structures. They are home to unique biological communities that live on and around the black smokers. On land ecosystems are usually supported by photosynthetic organisms. On the bottom of the sea, there is no sunlight for photosynthesis. In addition the pressure that exists at the bottom of the sea is much greater than at sea level. The water is also very cold, barely above freezing, except at the hydrothermal vent where it is extremely hot. Any organisms that live on the sea floor must be able to live without sunlight and under extreme pressure and in extreme temperatures. These ecosystems rely on the earth’s internal heat and the mixing of hot and cold sea water to produce biologically useful chemicals rather than sunlight for their energy. Bacteria and archeae form the base of the ecosystem. They are able to turn the chemical energy into biological compounds. They in turn are sources of food and energy for higher organisms including worms, clams, crabs and fish.