DID YOU SEE THE GOOGLE ADSENSE ADS ON THE RIGHT?
1) WHY DO WE DISCUSS HYPOGENIC CAVES
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Two posts ago, we discussed bacteria in caves and I promised you more about them. Here it is.
In the last twenty years, cavers have discovered a few caves formed not by surface waters like the one we usually know but by gases and waters seeping from the deep volcanic parts of the earth crust. Often, these caves do not have any communication with the outside world, a fact which explain why we have not discovered them earlier. They are called "hypogenic caves".
The true wonder is that these caves are full of life, archaic life originating in long past geologic times when our atmosphere was not choked with oxygen. They are exactly what I need for my bactorgs.
In this post I will tell you more about two of them: Cueva de Villa Luz in Mexico ( an intermediate cave just at the border between hypogenic and normal caves) and Movile Cave ( a true hypogenic one) in Romania.
If you want to read a report on a fossilized hypogenic cave, do a Google search on "Grotte du chat, Daluis (in French)". Look also the sites devoted to Frasassi cave (Italy). Finally, look also at the many sites devoted to Lechuguilla cave, one of the most beautiful cave known to man. For Lechuguilla, I give you just the site of a short report on a trip in Lechuguilla by Michael Ray Taylor, a caver , professor, journalist and writer specializing in cave bacteria, if you are interested, you should read his book "Dark Life: Martian Nanobacteria, Rock-Eating Cave Bugs, and Other Extreme Organisms of Inner Earth and Outer Space (Scribner, 1999)". Please... do a search on Lechuguilla and on all the caves I have been mentioning... wonders are awaiting you, just a few clicks away.
2. CAVE LIVING BACTERIA AND CREEPY CRAWLIES
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We will discuss two caves in which our bacteria are living; Villa Luz and Movile. The home of bactorgs in WE SHARE is inspired from them but needs a lot of modification to exist in Provence (different climate and geology) and fit my purpose (development of an eon-traversing bacterial community, communications with the outside).
2.1 CUEVA DE VILLA LUZ (TABASCO, MEXICO)
A transition between hypogenic and normal caves
Choking with sulfur oxide (H2S and CO2), having all its galleries coated with strongly acidic slime, a cave in south eastern
You see here a map of the cave.
As you can see, it is not really a pure hypogenic cave (i.e. one having no communication with the outside, far from it. Instead, it has lost of outside communications: the resurgence and all the side entrance pits through which light, heat, gases and all sorts of animals may enter the cave. I see Villa Luz as an intermediate case; a transition between almost hypogenic in its farthest recesses and a normal cave near the resurgence. This is neat... In my novel, I need a way for a truly hypogenic bacterial community to communicate with the surface. Something like Villa Luz might fill the bill. Of course, I will have yet to invent a nice little twist to have it at a depth of about -600 meters.Note: Villa Luz is a tropical cave warm and filled with life. My novel takes place in Provence... I will have to adjust for this... Provencal caves ar e almost alpinecaves. Life does not fill them.
Anyway, as a transition cave, Villa Luz has a lot to teach us about hypogenic ecosystems. Let's discover it.
THE VILLA LUZ ECOSYSTEM
As seen on the map, a river rich in H2S enters the cave in its more distal parts (left side) and H2S is also seeping from cracks in the soil connected to deep volcanic sources and pockets of gas. The river flows through the whole cave from left to right and exits through the entrance. On its way, it creates a series of small ponds. MAny fishes live in the ponds closest to the entrance (sardines, the Indian name of the cave is indeed "cueva de las sardinas"). This unusual abundance of life is easy to understand. These fishes eat all sort of living matter flowing out from the deeper recesses of the cave and transported by the river.
Indeed, the Cueva de Villa Luz's fishes are linked, as upper level predators, to a highly astonishing and extensive food web living in the dark in the ponds and passages farthest from the entrance. Thefood web members depend for energy not on photosynthesis from sunlight (there is none) but on an inorganic chemical process: oxidation of sulfur compounds.
When the explorer James Pisarowicz first entered Cueva de Villa Luz in 1987, he was flabbergasted by its "out of this world" geochemical features. The following description is modified from his paper: "Everywhere I saw yellow sulfur, white gypsum crystals, and colored slimes coating the walls. The "rotten egg" odor of hydrogen sulfide was almost unbearable. Hanging from the ceilings were strange stalactites that dripped sulfuric acid. Their examination showed later that they were massive colonies of sulfur-oxidizing micro-organisms. They looked really like rubbery stalactites made of mucus, so I dubbed them "snottites"...
You might have explored caves for years everywhere in the world, nothing prepares you for Villa Luz.
Indeed, as I have said before: it is hypogenic.
This means that it is not, like most caves carved out from entrance to bottom by carbonic acid, the compound that forms when rainwater picks up carbon dioxide from the air. In these normal” caves, the mild carbonic acid, the same we drink in beer and soda, seeps into the limestone cracks and, over geologic times, dissolves the rock and widen the caves forming the passages, pits and rooms we are used to see in caves.
Villa Luz like a few other caves in the world tells us a totally different geochemical story. These caves have not grown from mildly acidic waters coming from the surface. Instead, they have been, at least partially, carved by the strong sulphuric acid and chemical reactions made possible by the high sulfur content of the water rising from cracks in the soil connected to deep volcanic chambers in the earth crust.
Such hypogenic caves (i.e. formed from below) may, for millenia be carved by the acid coming from the deep earth’s crust without any connection to the outside world, no oxygen connection. They may exist as chambers totally isolated from outside and thus unknown to us.
Obviously, Villa Luz is not isolated... but one knows such an isolated hypogenic cave, called
Now anhypogenic cave may not stay isolated forever. If there is deep water rising in the cave, it may slowly carve a way out and meet a surface cave. Then we will have a sulfurous spring somewhere.
Of course nothing precludes also such an isolated cave to encounter after many millenia a normal flow coming from the surface and having formed a normal cave. Then we have a mixed situation where some parts of the cave are hypogenic and other are formed from the surface. Villa Luz might be such a cave (or is it formed only by deep waters flowing out?).
On the map given above, you see a series of rooms and ponds going from the deepest parts to the entrance. The ones close to the entrance have obviously an atmosphere rich in oxygen (see the pits). Eexcept for the richer than usual life present in them, they have many characteristics of normal caves at these latitudes. As you travel deeper and deeper into the cave, you go into more and more strange passages, more and more characteristic of hypogenic caves: a choking atmosphere, drops of skin burning sulphuric acid, and most astonishingly, a teeming life.
Indeed, hypogenic sulfur-based caves are not formed solely by inorganic chemical reactions (rock dissolution by acid). They are also carved and, literally, made by the enormous quantity of microbial life forms they support. Basic in these life forms are the bacteria. They derive their energy from inorganic chemical reactions (literally, they are rock eaters). They metabolize the H2S dissolved in the water and use the oxygen from the CO2 in the cave's atmosphere to produce sulfuric acid, a strong acid indeed since it is the one used in car batteries.
Question: I am not at all clear about the last sentence. Where does this oxygen comes from in truly hypogenic caves, from CO2? Then where is CO2 coming from? I am just no enough of a chemist to know. What is a truly sensible reaction mechanism?
The sulfuric acid then reacts with the rocks. It does not completely dissolve it but converts limestone into gypsum (calcium sulfate) forming beautiful white crystalline structures (needles, trees…). Gypsum falls into the stream and, being very soluble in water, it is then transported out of the cave. With time, more limestone is transformed into gypsum and the cave widens.
Indeed, sulfur-eating bacteria form the basis of the ecosystem (food web) of Villa Luz. They oxidize sulfur to get the energy they need and use thus carbon dioxide, water, and sulfur as the basis for their life. These sulfur eating bacteria are not isolated. Other bacteria eat them. All together, bacteria form huge mats and biofilms (veils in water, mats on rocks, snottites). Small invertebrates (e.g. innumerable midges and worms) graze on these slimy mats. Spiders prey upon the bacteria eaters.
As we have said before, the most spectacular form of bacterial biofilm found in Villa Luz is made by “Snottites”, slimy, rubbery chandeliers hanging from the ceiling or the walls and made entirely from many species of coexisting bacteria and a a complex biofilm structuring material. Small worms and mites live within and on the snottites; spiders walk their nooks and crannies.
The fishes in the external ponds (Poecilia mexicana) eat midges and sulfur-oxidizing bacteria.
As you see from the maps, Villa Luz has many entrances through which skylight can come in and visiting bats can fly and prey upon the ecosystem. This certainly couples Villa Luz’s ecosystem to the outside world and makes the story of Villa Luz much more complex than the one of a purely hypogenic cave. Nevertheless, it clearly shows how a sulfur based, oxygen fearing ecosystem can develop in an hypogenic cave. I will need such a cave, truly hypogenic in some parts but communicating with the outside world in other.
This is all I want to tell you for now about Villa Luz. In the next post we will discuss another hypogenic cave, a much purer one, Movile cave in Romania.
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