Imagine you are on vacation, on the coast of the beautiful Greek Island of Zakynthos. You head north, towards a remote diving spot near the city of Alikanas. And there, you see something that catches your eye, circular shapes strewn across the sea floor. As you get closer, you see geometrical slabs, set side by side, like a paved road. As you feast your eyes on the shapes, you dare to hope: ‘I’ve found it! Ulysses’ lost palace! The city of Ithaca is spreading out before me’. But you’d be wrong.
“As an archaeologist, I would say, ‘yes, this looks like the remains of an ancient civilisation’,”says Aris Sichlimiris, archeologist and MA student of classical archeology at the University of Athens.
Much like Aris, when amateur archeologists first identified the ‘sunken city’ of Alikanas, they were fooled by the perfectly geometrical ‘column base-shaped’ and ‘slab-shaped’ structures of white rock standing out against the wild sea floor.
Like most of Greece, the Zakynthos region is rich with history. “There is Mycenean history in the region, colonization of 6th century BC, it was also on the route connecting Greece and Italy in the antiquity”, says Aris. But most importantly, “it is a point were it is thought the mythical city of Ithaca could rest”. With the prospect of precious ruins being discovered, the Ephorate for underwater research rushed a research team to the site to authenticate it.
However, upon arrival, the team were not convinced. Lack of other traces of human civilization, such as pottery and tools, prompted the team, led by archeologist Ms. Magda Athanasula and diver Mr. Petros Tsampourakis, to contact outside help. With a mineralogical analysis, the truth transpired: this was a naturally occurring geological phenomenon.
“Micheal Stomatakis [geologist at the University of Athens and co-author of the paper], had already looked at what minerals cemented up this sediment, and he determined that these were dolomite-rich,” tells Julian Andrews, Professor and geologist of the University of East Anglia (UEA).
Julian Andrews is the lead author of the paper, published this month in Marine and Petroleum Geology. It proves that the Alikanas site is the result of an odd geological occurrence.
“The most significant thing we did here at UEA [was the] stable isotope work, where we looked at the carbon molecules. That carbon molecule has a very negative carbon isotope signature, [which is] indicative of methane.”
With this valuable information, Julian’s team were capable of reconstructing what had led to these fantastic structures.
“Bacteria [in the sea floor sediment] use the carbon in the methane for fuel,” says Julian. “A by-product of that reaction, hydrogen carbonate forms in the sediment, and that basically allows dolomite to precipitate.”
The dolomite-rich ‘column’ or ‘slab’ are “really a matter of how the gas is flowing through the sediment. When the gas is flowing in a focused pipe or tube, the bacteria cluster around [the gas] and they naturally form a circle around it. If the gas is now bubbling up through the sediment more widely, when it encounters the zone where the bacteria are living, and that’s when it gets to work. So rather than forming a pipe, they instead from a sheet.”
Julian tells us that these geological structures are not uncommon, but have very seldom been observed in such shallow water as these, only five meters in depth.
While this is not an Earth-shattering discovery for geology, and archeology will still have to find the missing city of Ithaca, Aris tells us that “even a hundred years ago, archeologist could have seen this phenomenon and created a whole story about the site. It is thanks to geology and modern sciences that modern archeology can build a real vision of antiquity.”
Guess we’ll just need to keep looking then…
Marianne Guenot is studying for an MSc in Science Communication.