This ghostly undersea spot testifies to the exchange of fluids from the Earth’s crust to the surface, across the ocean floor. Here we are in Paleokuri Bay on the island of Milos, Greece, where shallow hydrothermal activity is producing distinct yellow deposits of sulfur and arsenic and white bacterial mats that appear almost bright.
Circulation of hot water deep in the crust, or “hydrothermal”, is widespread on Earth. It is favored by the proximity of heat sources, such as magma chambers, and associated hydrothermal flows are responsible for about 25% of the Earth’s internal heat loss. In addition to these thermal effects, hydrothermal processes have a direct impact on the surrounding biodiversity, with the evolution of specific fauna and flora.
These hydrothermal vents are well described for very deep environments, especially along Ocean Hills.
But there are also hydrothermal systems close to the coast off the island of Milos or Taiwan for example, at depths of less than 200 meters. While some Shallow sites have been identified Worldwide, they are no less studied, and their geometry, time evolution and associated energy flows are not well known.
We study these systems to understand the exchanges between solid land and oceans and the evolution of ecosystems in extreme environments.
Milos Island and Paleochori Bay
In the southern Aegean Sea and on the Cyclades archipelago is the most extensive shallow hydrothermal system in the world – and one of the most studied today. In the Gulf of Paliokori, southeast of the island of Milos, intense hydrothermal activity extends from the shore to a depth of more than 200 meters, or about 1.5 kilometers, by swimming.
This activity is manifested, among other things, by emissions of acidic liquids with a high temperature, on the order of 100 ° C. These liquids contain gases (carbon dioxide and methane) and Mix with sea water during deep circulation. This “crustal excursion” also allows them to become salty, sulfurous, and Rich in arsenic and other dissolved gases.
[Près de 80 000 lecteurs font confiance à la newsletter de The Conversation pour mieux comprendre les grands enjeux du monde. Abonnez-vous aujourd’hui]Hydrothermal vents are often associated with yellow or orange deposits of arsenic sulfide, and white deposits of mineral origin. It consists of a mixture of silica and sulfur associated with bacterial mats. These deposits are visible from space on satellite images to a depth of 30 meters, and allowIdentify spots, linear structures, and polygonal structures produced on the surface of deep convection cells.
Multidisciplinary project
Drone and autonomous vehicle image data obtained by our team in 2019 make this possible map these structures she has Resolutions close to one centimeter.
Temperature measurements within these structures shed particular light on specific thermal mechanisms: for example, white polygonal structures identified in underwater images show higher temperatures (above 50 °C) than neighboring sediments (from about 24 °C) and are often associated with with domains “biological disturbance”Reformulation of sediment by organisms.
Our results provide an overview of this shallow hydrothermal system and the regulation of fluid circulation across the ocean floor. They provide preliminary perspectives on system heat fluxes and on The microbial communities controlled by this hydrothermal activity.
