Speleothems in Florida's Underwater Karst

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Speleothems in Florida's Underwater Karst

Postby CaverCraig » Feb 22, 2008 11:35 am

Carbonate platforms in places such as the Yucatan and the Caribbean, which are currently near sea level are loaded with speleothems. The vast majority of these speleothems are currently under water. During periods of glaciation these caverns become dry due to lowering sea level and it is at these times when the speleothems are deposited which makes them great paleoclimatic markers. Some of these speleothems have been collected form depths as great as 50m inferring that sea level must have been down that much at the time for them to deposit.
The question now is why in Florida a similar karst environment to those mentioned above, do we not have speleothems deposits in under water caves?
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Re: Speleothems in Florida's Underwater Karst

Postby DeWayne » Feb 22, 2008 1:47 pm

The age at which the caves formed. Most FL spring caves are younger than the last glacial age, so they have never seen prolonged periods of dry that would facilitate the formation of speleothems.
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Re: Speleothems in Florida's Underwater Karst

Postby Ralph E. Powers » Feb 22, 2008 3:30 pm

DeWayne wrote:The age at which the caves formed. Most FL spring caves are younger than the last glacial age, so they have never seen prolonged periods of dry that would facilitate the formation of speleothems.
I would think that there are formation growth going on in underwater caves but not the classic soda-straws, stalactites, stalagmites, but other crystal like growths are probably occurring in some of the fresh-water submerged caves. Also I would think that some of the caves still have a high salinity content to prevent even those types.


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Re: Speleothems in Florida's Underwater Karst

Postby Teresa » Feb 22, 2008 5:32 pm

Speleothems rarely form in springs because the water is flowing, and the passage is usually completely water filled. Most underwater speleothems (botryoids, rims, actual crystals) require oversaturation of the water with respect to calcite for the calcite to fall out of solution and land somewhere. The calcite coming out of solution cannot be swept away before it nucleates on a wall or a rock or somewhere. This doesn't happen in most springs, because of four things: the water is flowing because of new water entering the system, thus diluting the calcite saturation; 2) nucleation sites for calcite deposition are 'scraped clean' by the flowing water and 3) if you are actually getting water high in sodium, chlorine and magnesium (sea water) into the system, the magnesium at high levels inhibits the formation of calcite and 4) in a totally phreatic system there is no place for CO2 to escape, even if the water is oversaturated and it wants to.

To have speleothems, even in limestone, you have to have too much calcite or too little dissolved CO2. The above is a SWAG generalization; local mileage may vary.
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Re: Speleothems in Florida's Underwater Karst

Postby ggpab » Feb 22, 2008 8:46 pm

Wow - Great question.

As Teresa mentions, there is only limited potential for underwater calcite deposition and is highly unlikely in passages with high flow rates. For the sake of arguments lets only consider speleothem calcite formed above the water table, which are all the pretty stalagmites and stalactites, and that are now simply found below the water table. ie - they have been drowned.

Water levels in coastal aquifers is a function of three boundary conditions - 1. Speleogenesis and the existence of high flow path rates to efficiently drain the aquifer, 2. Climate which controls how much water there is in the aquifer. Since these are coastal aquifers this also means how high the water table is above the saline water. 3. Sea level.

1. Speleogenesis. Most (but not all) of the caves in the Yucatan are relatively very shallow with speleogenesis linked to 'mixing corrosion' where the infiltrating rain water hits the water table and also importantly at the fresh-saline halocline mixing zone. This is a very efficient chemical drill for making caves. The halocline in the Yucatan is shallow, being only ~10 m at the coast, and slopping deeper to ~ 100 m in the middle of the peninsula. Still quite shallow.
Speleogenesis in Florida has played differently for a variety of reasons, which I would argue are related to structural geology and minerology, the Florida rock having lower primary porosity and permeability (the small holes in the rock and how well interconnected they are), and also that the Florida rock isn't nearly as pure as that of the Yucatan which only has 5% or less insoluble residue after you dissolve the rock. In short, in Florida you have dirt whereas in the Yucatan it is very limited. The overall effect though is that volume of fresh water in Florida is very much larger than that in the Yucatan. The depth of the halocline is very deep in Florida, being 300 m or more. I have been hunting for direct observations of the depth of the fresh-saline halocline in Florida for over five years now, I am resigned to the likely fact that not even the USGS or the Florida Geological Survey have mapped out the depth of the fresh-saline interface inland from the coast, with most 'data' based on computer modeling of where it should be. The big flow caves in Florida punch through the fresh water part of the aquifer driven by probably much more subtle geochemical drives compared to the Yucatan and are often at some significant depth being 30 - 100 m below the water table. In the Yucatan, the principal depth of cave development are more like water table, 5, 10, 20 m.

2. Lets ignore climate for now.

3. Sea level. Given the much deeper average depth of passages in Florida, and that alot of what has been explored is some distance inland >>10 km from the coast, then even if you look at the minimum sea level at - 120 m lower than present over the Quaternary (the last 1.65 million years) you still have flooded caves. Ergo speleothem deposition to be reflooded. Most likely that most of the Florida caves were continuously flooded.
What you think of as the flooded Yucatan caves are all located 10 km or less from the Caribbean coast. There is alot of it, but is all squished in a thin strip. If you drop sea level to -120 m during the last glacial then you get almost a near direct drop in the water table to that level as well in these caves. Lots of speleothem deposition everywhere.

However the lower sea level is, the more deeply into 'glacial' periods you are, and the mores likely the region is to be arid with not enough water percolating into the ground to create speleothem. Also, the major factor in dissolving calcite is the CO2 in the rooting zone (NOT carbonic acid in the atmosphere), and so it is cold, dry, and with limited solid CO2 since the vegetation is all stressed. This can reach a tipping point shutting down speleothem formation. Now you can see why deep speleothem are rare - the cave has to be in the right conditions and just the right location to be drained AND climate and vegetation still have to be adequate for calcite deposition to not have been shut down.

I have heard of some deep speleothem from Florida, but I would love to know more. I suspect that they may be in caves very close to the coast first of all, and second of all I am wondering if they are true speleothem or other sedimentary forms that have been mistaken for them. If there is deep speleothem in Florida (ie > 50 m) then it is going to pose some real challenges in getting any information from them because they may well be older than the Quaternary, and dating calcite older than ~500 000 years old is - well - still experimental.

Water table caves which in Florida do have speleothem? That is a whole different story.

Anyway - my 2 + 2 cents worth.
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Re: Speleothems in Florida's Underwater Karst

Postby CaverCraig » Feb 22, 2008 10:19 pm

Good ideas, I think Trish's idea of speleogeniss is most fitting. I talked to some knowledgeable staff at Florida State University about this and they say it's really a mystery and nobody really knows why there isn't speleothems in underwater Florida caves. I talked to two different geologist and they both thought that it might be a matter of hydrology. The sea level may have been dramatically less than the water table due to high hydrostatic pressures. There may have been such a high hydrostatic pressure that the water table Floated well above sea level keeping the caves submerged even during the Ice Age preventing the growth of most speleothems. In places like the Yucatán and the Caribbean islands the recharge area isn't so large as to build up a large hydrostatic head. In contrast Florida has a huge reached charge area north of it, which recharges the Floridian aquifer. Florida's huge recharge area gives it a high potential for higher hydrostatic pressures which may have made it possible for the water table to float well above sea level keeping the submerged caves submerged.
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Re: Speleothems in Florida's Underwater Karst

Postby Squirrel Girl » Feb 23, 2008 3:34 pm

You might check into the work of Lewis Land. He did his dissertation on underwater sinkholes off FL. Now he's a hydrologist in Carlsbad, NM, working for New Mexico Tech. He's very nice and probably wouldn't mind if you emailed him, I'm sure (or called him).
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Re: Speleothems in Florida's Underwater Karst

Postby tncaver » Feb 23, 2008 8:48 pm

I could swear I've seen video on TV about some of Florida's major underwater caves that were full of formations.
These were very typical stalactites and stalagmites that were formed while the caves were dry. The caves
are now underwater but the formations are basically frozen in time. The fresh water isn't dissolving or
adding to the formations. The water was crystal clear so long as the silt was not disturbed.
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Re: Speleothems in Florida's Underwater Karst

Postby Teresa » Feb 23, 2008 10:11 pm

tncaver wrote:The caves are now underwater but the formations are basically frozen in time. The fresh water isn't dissolving or adding to the formations.


I'll believe that perhaps a few of the Florida caves have some speleothems in some parts of them. Never say ALL or always in science, though I've not see video of such. However I have my doubts that the fresh water isn't affecting the stal, unless it is a constant, perfect 7.0 pH. Some, (not all) of FL's divable springs are pretty high in tannic acid, and acid is acid.
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Re: Speleothems in Florida's Underwater Karst

Postby tncaver » Feb 24, 2008 9:06 am

It is quite possible the video I saw was not shot in Florida. My memory suggests it was. The way I recall it,
it was a video (an entire show on TV) on the exploration of underwater caves in Florida and there were stalactites
and stalagmites in the caves. It is entirely possible I am wrong about this. Maybe it was video from Yucatan or
some other area known for underwater caves with crystal clear water.
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Re: Speleothems in Florida's Underwater Karst

Postby CaverCraig » Feb 24, 2008 9:59 am

Good argument, a lot of people think that the stalagmites and stalactites and other formations may have gone back into solution. However, why wouldn't the formations found in other underwater caves also be dissolved? Theoretically, they should have been exposed at the same time and underwater at the same time having the same time to dissolve back into solution. The caves of the Yucatán and Caribbean showed little or no evidence of dissolution, it would be hard to believe that the water chemistry in Florida would be so much different as to dissolve all speleothems.

I read a post mentioning that it was bad science to say all underwater caves in Florida lack speleothems. I agree, however I've talked to many cave divers and posted on the cave divers forum about sightings of speleothems and there are two places that they've been reported. The first place is and warm mineral Springs, the formation is relatively shallow and is located in the basin and the other reported formations were found in Eagle's nest cave at a depth of 100 m a few cave divers claimed to have seen a small pile of broken stalactites on the floor. I would like to see those so-called stalactites for myself and determined if in fact they really are stalactites or some sort of sedimentary structure.
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Re: Speleothems in Florida's Underwater Karst

Postby tncaver » Feb 24, 2008 1:40 pm

Perhaps the difference in underwater caves that do have formations has something to do with the
type of water involved. Some caves are filled with fresh water while others are filled with salt water
and some have both. The caves I remember in the video had crystal clear water and were full of
stalactites and stalagmites that had obviously formed at a time when the caves were dry. The
divers were exploring the caves with under water scooters.
However, it is possible this was not video of caves in Florida. Anybody else seen these caves on
TV? :snorkling:
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Re: Speleothems in Florida's Underwater Karst

Postby wendy » Feb 24, 2008 3:12 pm

tncaver wrote:Perhaps the difference in underwater caves that do have formations has something to do with the
type of water involved. Some caves are filled with fresh water while others are filled with salt water
and some have both. The caves I remember in the video had crystal clear water and were full of
stalactites and stalagmites that had obviously formed at a time when the caves were dry. The
divers were exploring the caves with under water scooters.
However, it is possible this was not video of caves in Florida. Anybody else seen these caves on
TV? :snorkling:


ya that sounds like some caves in Mexico and not in Florida. I have seen no formations in Florida underwater caves, although I have heard of one or two in some deep caves here. Even some of our dry caves don't have formations. But we do have a lot of fossils in our caves, both dry and underwater.
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Re: Speleothems in Florida's Underwater Karst

Postby akcaver » Mar 20, 2008 12:20 am

I have to discount the theory that the caves in Florida are younger than the last glacial maximum when sea level was approximately 120 m lower than today. This was about 20000 years ago! Multiple speleothems from Florida caves have been dated at 50-70000 years, and the age of the limestone formations where the caves are located are 40 million years or older. There are caves inland (30-60 km) that have speleothems right around the water table, some are submerged if the table is up, and other times they are not. I tend to go with the theory that the hydrostatic head of the aquifers were so high that the water table did not lower significantly in N Fl and thus the caves have always been flooded.

If there were speleothem growth and the caves flooded, the speleothems would not have dissolved completely away in the fresh water. Calcite will dissolve in fresh water with a pH near 7 until the water is saturated with respect to calcite, which doesnt take much. The theory is the same as taking any mineral and putting it in fresh water; some will dissolve and some will not.

Good question Craig, maybe we can discuss it sometime. :grin:
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Re: Speleothems in Florida's Underwater Karst

Postby Tom Gilleland » May 29, 2008 6:11 pm

CaverCraig wrote:Good argument, a lot of people think that the stalagmites and stalactites and other formations may have gone back into solution. However, why wouldn't the formations found in other underwater caves also be dissolved?


I've dove some island caves in Bonaire and Cayman Brac where the underwater passage had fresh water at the top and saltwater below. The freshwater section was actively dissolving away the formations. The salt water below was not. It all depends on the chemistry of the water. I think there is some discussion of this in the island karst model papers.

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