How do we find deep sea hydrothermal vents?
Vents are found by tracking their chemical signature.
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Wetting a finger to find the wind
The heated, mineral-rich hydrothermal fluids are less dense than the surrounding sea water and rise to form a plume above the vent. Like the smoke from a chimney, this plume gradually mixes with the surrounding water; its chemistry changes as minerals precipitate out and it cools. Like the smoke it can be “blown” by currents.
CTDs reveal much about the water column
Researchers begin their hunt by looking for chemical anomalies in the water column that are characteristic of the reduced chemicals in hydrothermal fluids. Early hunting techniques involved using a CTD; a rosette of water collection bottles plus meters for measuring Conductivity, Temperature and Density, among other things. Connected directly to the ship researchers can follow the profiles of the various meter outputs and watch for anomalies.
The profile peaks can be correlated to the results of water samples taken at that particular place in the water column. It is a painstaking process. The closer to the sea floor the anomaly, the greater the likelihood that a vent is near-by. However, a large anomaly higher in the water column might indicate a very productive vent. Researchers need to combine this chemical date with data about the geology of the sea floor, and oceanographic information about local currents.
More about CTDs: what is a CTD using a CTD
AUVs: Automating the search process
Autonomous Underwater Vehicles (AUVs) were developed originally for applied industrial and military uses, but the technology is also valuable for obtaining research information. An AUV is launched from a ship but can operate independently of its mother ship. They can be equipped with different sampling equipment modules and programmed to undertake, for example, a square-grid search of an area, where they can take systematic measurements of the water characteristics as well as carrying out high-resolution mapping.
Learn more: Exploring the deep-sea with autonomous vehicles
The AUV HUGIN has mapping capacity that is accurate to within a few 10s of centimetres! This information combined with the AUV and CTD chemical and temperature data provide relatively detailed overview of the seafloor and water column above. Based on the information the AUV collects, the ROV, with its additional “eyes on the ground” video capacity, is sent down to conduct the final search for likely vent locations.
Post-doc Tamara Baumberger explains that the improved technology may mean that the search process has become less intense, but it is always fascinating and exciting to be part of an exploration effort. The newest vent is located further away from the Bear Island Fan sedimentary processes than is Loki’s Castle, and is also some distance from the Jan Mayen hot spot. It may therefore provide CGB researchers with new insights about arctic ridge venting.