Back on the ship chief ROV pilot Aggelos Mallios maneuvers Super Achilles over unusual sediment mounds observed during the beginning of the dive. Super Achilles sent live video of the site to scientists stationed on board Aegaeo to communicate dive plans and sampling strategy in real-time to the Thetis ROV. Click image for larger view and image credit.
Joint Operations
July 1, 2006
36 N, 25 E
Dr. Richard Camilli
Scientist
Today I will complete my third dive mission in Thetis at our deepest site yet, 350 meters (approximately 1,150 feet) at the island of Santorini. Santorini is a large geologically active volcano classified as a caldera. Our dive mission is to search for other hydrothermal seeps like those observed at Milos. Today we will descend into the bottom of the volcano to determine if an area within the crater is venting hydrothermal fluids. Investigating this site is important for our understanding of the volcano’s activity. Unlike Milos, which is built from multiple smaller volcanoes, Santorini is one gigantic volcano.
Approximately 3500 years ago, during the time of the ancient Egyptians, the Santorini volcano exploded in a massive eruption (it is thought to have been one of the largest eruptions within the past one million years). Like Pompeii, the Minoan city of Akrotiri was buried under a thick layer of ash that resulted from this eruption. However, unlike Pompeii, human remains were not found, suggesting that the inhabitants may have left the island before the eruption. Some people believe that Santorini is the mythical island of Atlantis, mentioned by the ancient writer, Plato. Not much is known about the ancient history of Santorini. The inhabitants of Akrotiri disappeared without a trace. Many historical and scientific mysteries still surround this island.
It is another beautiful sunny morning as we are lowered into the water. Sunlight cannot penetrate seawater more than about 100 meters, and the deeper waters remain in perpetual darkness throughout the world’s oceans. So, by the time we reach a depth of 200 meters our day turns into night. We switch on the submersible’s external lights as Thetis plunges into total darkness. At 250 meters we are surrounded by strange looking iridescent organisms that only live in these deeper waters. We touch down beside a rocky outcropping at 350 meters depth.
Our survey begins by first examining the area suspected to be hydrothermally active. The Gemini mass spectrometer data immediately suggests this hypothesis is incorrect. The water conditions at this site are the same as surrounding water and lack any of the telltale signs of hydrothermal activity that we detected at Milos (increased concentrations of carbon dioxide, hydrogen sulfide, and methane). Knowing this while still on the dive allows us to immediately communicate our discovery with our Greek scientist colleagues (including biologist Aleka Gogou, geologists Dimitris Sakellariou and Christos Anagnostou) onboard Aegaeo. Over the next few minutes we make a detailed second examination of the chemical data and quickly discuss the scientific implications, via the “underwater telephone”. Based on our latest clues and combined expertise in biology, geology, and chemistry a new hypothesis emerges and we immediately revise the dive plan. The HCMR Super Achilles robot is on its way down and will soon join us.
Thetis switches on its external lights as the submersible descends beyond the depths where natural sunlight penetrates. The eight dive of the cruise, this dive was the deepest conducted during Project PHAEDRA 2006. Click image for larger view and image credit.
After reaching the seafloor and reading signs and sensors indicating no hydrothermal activity is present, Rich Camilli and Kostas Katsaros ìcallî scientists on the surface to revise the dive plan. Midway through the dive, the submersible is joined by HCMR ROV Super Achilles to conduct a survey of the site. Click image for larger view and image credit.
We gather water and sediment samples from small and unusual, ½ meter diameter mounds that we encounter on the seafloor. These mounds are made of a yellow-orange material loosely collected above the grey mud and lava rock bottom. They are easily disturbed by the sub’s propellers, so we have to be very gentle while we collect our samples. The mound’s material reminds me of the little bits of herbs that settle to the bottom in a container of vinaigrette salad dressing.
On one of the mounds we encounter a small fish with unusual whisker-like appendages that protrude from either side of its gills. We watch for a few moments as it swims across one of the mounds while using its “whiskers” to feel its way along the surface of the mound. It appears to be hunting for some lunch, perhaps using these specialized feelers instead of its eyes in this dark environment. Our lights soon attract the attention of several squid lurking just out of sight. Occasionally they rocket into view and send out a jet of ink, resembling shooting stars. Other small squid approach the lights and wrap their tentacles around them, temporarily muffling the lights and casting large magnified shadows on the seafloor.
Midway through our dive mission we are joined by Super Achilles. Super Achilles is a remotely operated vehicle (ROV) that our colleagues at HCMR also use to explore deep sea environments. Back on the ship, chief ROV pilot Aggelos Mallios is at the controls, deftly maneuvering Super Achilles into position above the mounds. Together we complete our survey of these unusual mounds. Once we complete our sampling tasks and survey of the area the Super Achilles ROV swims back to the surface. After we receive confirmation that Super Achilles has been safely recovered and is back on deck, we receive permission to begin our half-hour long ascent to the surface. This dive mission and recovery proceeds so smoothly that it almost feels like another day’s work in our underwater office and the usual quiet commute back home, carpooling with Kostas.
It now seems likely that the sediment and mounds we encountered on the seafloor are a result of iron being consumed by microbes. Like the microbes at Milos, these microorganisms are probably chemosynthetic, in that they do not rely on photosynthesis to generate their metabolic energy. Unlike the ecosystem at Milos, the microorganisms that we found in the Santorini caldera probably get their energy from oxidizing, or “rusting” iron. Confirmation of this requires further analysis, but it was terrific to see the mission plan evolve in real-time based on the in-situ mass spectrometer data and to be able to conduct joint submersible–ROV operations.
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