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Meet Eratosthenes Seamount

View of Eratosthenes Seamount and the eastern Mediterranean Sea from the north.
J. Mascle/Géoazur, Nice, France & C. Huebscher/Institüt für Geophysik, Hamburg, Germany, MediMap, and ETOPO1

Tough to say, easy to enjoy. Educator at Sea Jason Pittman here, to give you a look at some of the reasons this beautiful seamount has captured the interest of Nautilus and her crew of scientists. Dr. Larry Mayer summed up those interests quite well in his recent interview here on Nautilus Live with one word: Exploration!

The Eratosthenes Seamount is located just about 95 km south of Cyprus. Its very flat, table-like top is 700 meters below sea level at its shallowest point, and 2,000 meters at its deepest, and extends about 70 km wide and about 45 km in length. Seamounts tend to form from volcanic activity under the ocean, and it has been hypothesized by earlier scientists that Eratosthenes may also be volcanic.

But when Nautilus came to the seamount two years ago her science team found a few surprises.

“Pockmarks” had previously been observed on the top of the seamount. Pockmarks are often caused by chemical fluid “venting,” or chemical-rich water rising up through the seafloor and into the ocean. So we expected to see fluid venting on the flat top of Eratosthenes. However, Herc's high-definition cameras allowed us to see that there was no fluid venting coming from these strange depressions in the seamount. The pockmarks turned out to be sinkholes. Five million years ago, the top of the seamount was above sea level. When sea level rose, it was eroded by rain and fresh water, which created caverns and caves. When the top of those caves collapse, it creates a sinkhole. Looking inside the sinkholes allows geologists to see the layers of rock that reveal a great deal of information about the seamount's history.

Perhaps even more intriguing is the tectonic activity going on at the seamount. Eratosthenes Seamount sits atop one of the northernmost points of the African plate which is being pushed toward Cyprus. As the African plate moves north and collides with the Eurasian plate, it will eventually slip under the Eurasian plate in a process called subduction. However, there is a significant crack across the flat top of the seamount, which is evidence that the seamount is resisting subduction. As the feature is being forced into subduction, chemical rich fluids are being squeezed out of cracks in the porous sides of the southern part of the seamount.

During our dive operations, we observed shimmering water that indicates these fluids are present, but unlike many other chemical seeps are not exceptionally hot. Most of the seeps are within 1 degree Celsius of the ambient water temperature, which is approximately 14 degrees Celcius.

Active Cold Seep Site

And this is where it gets exciting: These fluid seeps have become home to a very unusual community of organisms. A very special bacteria has the capacity to convert chemicals in these seeps into carbohydrate energy in much the same way that plants convert the sun's energy into carbohydrate energy. The process is known as chemosynthesis. Viewers of Nautilus Live will recognize these bacteria as the fluffy white bacterial mats that are often captured by Herc's cameras when we are looking at the seeps. Colonies of tube worms live in a cooperative relationship with the bacteria; food webs that include crabs, clams, and anemone all exchange this food energy.

Never before has such detailed visual documentation occurred on this seamount. I feel incredibly privileged to one of a the few group of people who have become well aquainted with this deep sea feature. Our dives on the Eratosthenes Seamount continue until August 26th. Join us on Nautilus Live and become a member of “Club Eratosthenes!”