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Scientific Cave Diving

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Scientific Cave Diving PAPER Scientific Cave Diving Thomas M. IIiffe ABSTRACT water caves including biological, geological, Department of Marine hydrological and archaeological investigations. Biology Cave DIVING IS ONE OF THE MOST TECHNICAL AND Faunal surveys of anchialine (coastal, marine) Texas A&M University at POTENTIAL DANGEROUS FORMS OF DIVING DONE caves in particular have relied on cave diving. Galveston today. It MAY INVOLVE USE OF MULTIPLE tanks, Galveston, TX REGULATORS AND GAS MIXTURES OR rebreathers, IN These caves typically have a surface layer of COMBINATION WITH powerjullong-range DIVER fresh or brackish water separated from underly- Curt Bowen PROPULSION vehicles, TO PENETRATE THOUSANDS OF ing saltwater by a well-defined halo cline (Iliffe, Advanced Diver Magazine METERS INTO SUBMERGED CAVE SYSTEMS WHERE 2000). Thus, it is only through diving that access Bradenton, FL DIRECT ASCENT TO THE SURFACE IN THE CASE OF emer- to the deeper saltwater layer in caves can be GENCIES is impossible. In ORDER TO CARRY OUT sci- achieved. A unique cave-limited fauna, consist- ENTIFIC STUDIES UNDER SUCH di.fficult conditions, ing primarily of crustaceans, has been collected INDIVIDUALS MUST BE HIGHLY COMPETENT AND using traps, plankton nets and visual collec- EXPERIENCED CAVE divers. In SPITE OF THESE prob- tions. These discoveries include more than 200 lems, NUMEROUS SCIENTIFIC INVESTIGATIONS IN THE .fields OF biology, ecology, microbiology, geol- new species with many higher taxa and even a ogy, HYDROLOGY AND ARCHAEOLOGY HAVE CARRIED new order of Crustacea-the Remipedia. A num- OUT BY CAVE DIVING scientists. Exploratory CAVE ber of these taxa, such as Remipedia, are primi- DIVERS HAVE PROVIDED THE INITIAL IMPETUS FOR tive living fossils with highly anomalous biogeo- THIS RESEARCH BY EXPLORING AND MAPPING graphic distributions, occurring in caves from UNDERWATER caves. both the Atlantic and Pacific. Biologically sig- nificant anchialine limestone caves are present CAVE DMNG SCIENTIFIC in Bermuda (lliffe, 1994), the Bahamas (Juber- ORJECTIVES thie and Iliffe, 1994), Cuba, Yucatan (Mexico) (Iliffe, 1993), Jamaica, the Balearic Islands and Cave Mapping Western Australia (Humphreys, 2000), while anchialine lava tubes occur in the Canary Islands Since the most accurate way to (Iliffe et al., 2000), Hawaii and the Galapagos describe a cave is to map it, most cave explora- (Iliffe, 1991). tion teams routinely survey and draft maps of The longest underwater caves on Earth their discoveries. Surveying is routinely done are found in the Yucatan Peninsula. Since sur- by measuring distances between stations using a guideline knotted at 3 m increments. Compass face rivers are lacking in this area, all drainage bearings along line segments between stations is subterranean through the porous limestone and water depth at each station is recorded, bedrock. At present, the world's longest under- along with distances to left and right wall, ceiling water cave is the anchialine Systema Ox Bel and floor. Water depths, measured with a depth Ha on the Caribbean coast of Yucatan with more gauge, provide information on the vertical dis- than 70,650 m of surveyed passage. Stable car- tance beneath the surface of the water table. bon and nitrogen isotope ratios have been used Electronic mapping devices have been used to to discriminate food sources in anchialine map some large cave systems. An automated caves from Yucatan and to trace their utilization digital three-dimensional wall mapper was used by cave-limited crustaceans and fish (Pohlman during the Wakulla 2 project. It consisted of an et al., 2000). Populations of chemoautotrophic array of 32 sonar transducers for measuring wall bacteria associated with halo clines, along with distances, plus sensors for measuring depth and organic matter from open cenote pools and over- water temperature, taking measurements at a lying jungle soil, were found to support the cave rate of four per second. Repeated survey of a ecosystem. Most troglobites (cave-limited spe- passage increased detail and resolution of the cies) are observed in the water column thus resulting map such that details as small as one implying that this is where they obtain their food. mm could be resolved. Control of the electronic Microbiological studies of underwater survey was done using waypoints within the caves have been conducted using sterile sam- cave determined by using low frequency mag- pling techniques (Brigmon et al., 1994). Visible netic induction beacons that could be precisely colonies of Thiothrix spp., a sulfide oxidizing located from the surface. mixotrophic bacteria, were found in 6 of the 8 underwater caves in Florida sampled by divers Cave Biology during the study. Since Thiothrix generates sul- In addition to cave surveys, numerous furic acid that can dissolve limestone, such bacte- scientific studies have been conducted in under- ria may play a role in cave formation. 36 • MTS Journal • Vol. 35, No. 2 Cave Geology and Hydrology inland from the Mediterranean, became sub- Geological studies have included the merged when the sea began to rise at the end isotopic dating of submerged stalagmites from of the last Ice Age, about 12,000 years ago. With the aid of radiocarbon dating, it was determined anchialine caves. Since such speleothems are that the images in the Cosquer cave were made only formed in' air by dripping water, they must during two different eras. The earliest drawings have formed during the Pleistocene Ice Ages of stenciled hands were created about 27,000 when sea level was substantially lower and the years ago, while drawings of land and marine caves were dry. At that time, so much water was animals, including cold-loving plains horses, removed from the oceans to form glaciers on ibex, huge ice-age deer, seals and great auks, the continents that sea level was lowered by 100 are some 18,500 years old. m or more. By measuring the thorium-ura- Numerous cenotes or water filled sink- nium ratios in sequentially deposited layers of holes in Yucatan were used as sites for ceremo- now submerged stalagmites, it is possible to nial offerings and sacrifices by the Mayans. Cave determine the time at which each layer formed diving archaeologists have discovered a wealth (Harmon et al., 1978). By lrnowing the depth at of artifacts from such sites. Cenote Xlacah is which the stalagmite was found and the age that located in the center of the ruined Mayan city it was deposited, it is possible to construct of Dzibilchaltun. Divers on a National Geo- paleo sea level curves from the Pleistocene. graphic Society expedition to this site in 1958, Cave exploration and mapping have recovered more than 6000 artifacts including contributed significantly to our understanding pottery and human remains (Marden, 1959). of subterranean hydrology. In the Wakulla Karst The cenote was explored to a depth of 44 m Plain of north Florida, mapping of a network where a large tunnel was found extending away of more than 42 km of cave passage has helped from the entrance pool. Thousands of addition hydrologists to understand the complexity of cenotes are lrnown from Yucatan, many of groundwater flow in the area (Werner, 1998). which are likely to contain Mayan artifacts. Similar cave exploration and mapping projects Prehistoric human remains along with along the Caribbean coast of the Yucatan Penin- Ice Age mammals including mastodons, saber- sula have better defined regional flow patters. tooth tigers and giant sloths have been found in The complex structure of the water col- springs and sinkholes in Florida. In 1972, umn in anchialine caves has been investigated archaeologists found an 11,000 year old, full with the aid of electronic water quality loggers human skeleton at a depth of 13 m in Warm made by Hydrolab and Yellow Springs Instru- Mineral Springs, neM Sarasota, Florida Similar ments. These instruments can record measure- remains of early man in North America have ments of depth, salinity, temperature, pH, dis- been recovered from Little Salt Springs. solved oxygen, redox potential and turbidity as frequently as once per second, thus providing highly detailed promes of the cave water column CAVE DMNG METHODOLOGY (Figure 1). The lead diver typically carries the XPloration and study of submerged caves is instrument with sensors held forward into undis- Ea highly specialized and potentially danger- turbed water. At the end of the dive, data from ous form of diving. As of 1999, 478 cave diving the instrument is downloaded to a computer for fatalities have been recorded, but only 47 of analysis and interpretation. In most anchialine the victims were trained in cave diving (Bozanic caves, all measured parameters show their great- and Halpern, 1999). In contrast to open water est variation in the halocline region (Iliffe, diving, cave diving presents a number of specific 2000). In some caves, multiple halo clines are and potentially life threatening hazards. First encountered. Comparison of water quality pro- and foremost, in cave diving, a rock ceiling is MES made using rebreathers, in contrast with overhead so that in case of emergency, a direct conventional scuba, indicate that scuba diving ascent to the surface is not possible. In most disrupts the physico-chemical environment and cases, it is necessary to exit the cave in the may adversely affect the endemic anchialine same way it was entered. Thus, a cave diver at fauna (Humphreys et al., 1999). 30 m depth, 300 m inside a cave needs consider- ably more air reserves and emergency planning Cave Archaeology than does an open water diver at the same Cave divers have made a number of depth. Other hazards include depth, decompres- important archaeological discoveries. In 1991, sion requirements, limited visibility, and psy- cave diver Henri Cosquer entered a submerged chological pressures. cave near Marseilles, France and discovered a Many of the safety procedures rou- wealth of prehistoric art in air-filled interior tinely used by cave divers today are based on rooms of the cave (Clottes and Courtin, 1996).
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