Explore the Deep Sea

Tools & Techniques

One way of discovering new hydrothermal vents.

A venerable vent hunter…

Diagram showing a plume rising from a vent.

In the 1980s, physical oceanographer Ed Baker pioneered a technique for finding hydrothermal vents using a CTD rosette to sniff them out. This instrument can measure temperature and light transmittance (how cloudy the water is) very accurately. So it can be used to detect the plume of water that rises from a vent site, rather like smoke rises from a smokestack.

…or rather, a plume hunter

Before sending the CTD rosette on its long trip towards the seafloor, the scientists first gather as many clues to where a vent site might be as they can: clues like the location of fault lines and bathymetry data (used to create maps of the seafloor). Then they take their best educated guess, and start fishing for a plume.

Raised and lowered like a yo-yo

The CTD rosette being lowered over the side of the ship. Image courtesy of K. Kusek.

Plumes typically rise about two hundred meters from the seafloor before losing their “lift” due to density changes, just like smoke from a stack often levels out in the atmosphere. To find a plume, the CTD rosette is towed slowly behind the ship while a winch operator moves it up and down at the same time (like a yo-yo — tow-yo — get it?). Zigzagging through the dark depths from near the bottom to a couple hundred meters above it, the instruments send their readings back to the surface. High above on the ship, researchers watch for the changes in temperature and light transmittance that indicate the equipment is passing into a plume.

Finding a plume is only the beginning

But finding a plume is not quite the same as finding a vent. Like smoke in the wind, the plume from a vent site might drift a long way from the actual site itself because of deep ocean currents. When you are fishing for those sites from two kilometers above, it can be quite difficult to pinpoint the vents themselves. A second tow-yo, parallel to the first, might give you an idea which way the underwater “wind” is blowing. Ultimately, to pinpoint the vent, it can be useful to send down an instrument that can photograph the seafloor in detail: for example, a submersible or a camera sled.

Next: TowCam, a towed camera