Explore the Deep Sea
Tools & Techniques
A set of instruments for detecting key information from seawater.
A vent finder
This large, odd-shaped collection of equipment has played a significant role in sniffing out deep-sea hydrothermal vents. It is lowered with a winch and crane, nearly to the bottom, and then gently towed along. It can be raised and lowered in height to sample at different depths; this is sometimes referred to as a tow-yo.
Many instruments, many talents
The water emitted from vents is so hot and buoyant that it continues to rise as it mixes with surrounding seawater, until it reaches 300-500 meters above the vents and becomes neutrally buoyant. These plumes are not only very slightly warmer than the surrounding seawater, they also tend to be “cloudy”, because they contain mineral particles. We can spot these particles using optical meters. Also, vent water is usually rich in certain metals like manganese and other chemicals like methane and helium. So we can detect plumes by measuring these chemicals, even when vent water is diluted as much as 10,000 time by seawater.
The CTD rosette carries a variety of instruments that help detect the plume of water rising from the vent:
- 10-liter bottles to take water samples (24 of them)
- A CTD set into the base: this measures conductivity (a measure of how saline the water is), temperature and pressure (a measure of depth)
- A dissolved oxygen sensor
- A transmissometer to sense particulate matter (how cloudy the water is)
- An altimeter to measure height above the seafloor (to about 300m)
- A fluorimeter to sense chlorophyll (the green pigment in plant material; this is not used in the dark depths)
Data from the instruments are transmitted up the cable to scientists on the ship.
From launch to recovery
While it is lowered and towed behind the ship, researchers in the ship's lab watch the data being sent back, looking for signs of a plume — such as spikes in the temperature and transmissometer readings. They can send commands down the cable to trip a bottle shut, trapping a water sample. This is often done at points below, inside and above the plume rising from a vent, so that the water chemistry of these different regions can be compared. Back on deck, the bottles are drained (and sometimes filtered). The seawater from inside is stored for later analysis.