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The moisture budget of a cave atmosphere is examined quantitatively. The results indicate that caves can be divided into two distinct classes depending on whether the cave atmosphere is or is not saturated. A further consequence of the theory is that greater climate fluctuations are to be expected in caves in which unsaturated conditions prevail. This generalisation may have significance in studies of cavern breakdown and in ecological studies in caves.
This paper describes an extremely simple form of barometer which is capable of measuring changes in air pressure of less than five pascals. The principle of operation, construction and use are described and examples are given of its use both inside and outside the cave environment.
Pressure of use of Jenolan Caves as a tourist spectacle has raised concerns about the wellbeing of the caves, so three related physical subjects were reviewed and investigated; the cave microclimate, the carbon dioxide in the cave atmosphere and dustfall in the caves. The microclimate has been shown to be dominated by several physical processes: in the absence of air movement, conduction and radiation dominate; in association with air movement, convective coupled heat and mass transfer tends to dominate energy flows. A new approach using boundary conditions and qualitative characteristics of transient fronts enables accurate measurement and analysis of energy, heat and mass transfer. This technique avoids the dimensionless number and transfer coefficient methods and is not geometrically sensitive. Conditions in caves are also determined by the capillary processes of water in cave walls. Air movement in caves depends on surface weather conditions and special problems of surface weather observation arise. A series of experiments were undertaken to evaluate the cave and surface processes. The physical processes that collect, transport and release dust were measured and described. Dust in the caves was shown to be carried from the surface, mainly by visitors. The concept of the Personal Dust Ooud is developed and experimental measurements and analysis show that this process is a major threat to the caves. New techniques of measurement are described. An accurate physiological model has been developed which predicts most of the carbon dioxide measured in Jenolan Caves, derived mainly from visitors on the cave tours. This model, developed from previously published human physiological information also predicts the production of heat and water vapour by cave tourists. The effects of carbon dioxide on cave conditions has been investigated. Details of a two year program of measurements in the caves are given. The generalised approach and methods are applicable to other caves, mines and buildings.
The Marble Arch cave is a high energy cave located in County Fermanagh, Northern Ireland. The first 500 metres of the system has been opened as a Showcave for approximately 13 years and has been visited by over half a million visitors since opening. Microclimatic investigations over a six month sampling period (31.7.96-10.1.97) found that the cave has a variable microclimate in response to, the surface climate, the caves hydrology and influences within the Showcave.
High positive correlation coefficient's were attained between the cave and surface air temperature. As distance increased into the cave correlation coefficients' decreased indicating a time lag. Air temperatures varied on both a temporal and spatial scale. Summer air temperature ranges of 2.1 °C were noted between sites within the cave, which increased to 7.1 °C during the winter season. The cave air temperature changed progressively from the entrance to the interior, decreasing in the summer and increasing in the winter months. During the summer months the mean surface air temperature (17.4°C) was greater than the cave mean air temperature (10.8°C). In the winter months the mean surface air temperature (1.9°C) was less than the cave mean air temperature (7.2°C). Site variability was generally greater during the summer months indicated by higher Coefficient of Variations.
The 'chimney effect' is noticeable in some parts of the cave as a result of surface and cave air temperature differences. Airflow within the cave changed direction in response to seasonal air temperature variations, flowing out of the cave during summer months and into the cave in the winter. Other processes such as the 'Entrainment Effect' were also evident. Airflow throughout the cave was generally weak, although in some parts of the cave was noticeable as a 'wind'.
The main river flowing through the cave was responsive to the seasonal cave air temperatures. During the summer months the water temperature once entering the cave decreases by approximately 2°C and increases by up to 7°C during the winter months. A relatively constant seasonal water temperature is maintained whilst travelling through the cave.
The largest air temperature variations occurred within the Showcave in which the presence of tourists and electrical lighting are believed to be partially responsible, the latter of which being the greater contributor. Results show that a tour of 18 people on average increased the surrounding air temperature by up to 1.3°C. The effect was reduced when a tour was moving past a point rather than remaining stationary in the same place.
Electronic lighting increased the overall air temperature throughout the Showcave. Each type of light used within the Showcave influenced the air temperature up to a metre away from the light source. Air temperature increases around the lighting was a result of the type of light used rather than the bulb wattage installed. In some cases the air temperature remained 2°C higher than the mean cave air temperature 1 metre away from the light source.
The paper presents some results of the karst geo-ecological system research. The first sphere of the karst-ecological system is the karst microclimate in accordance with the microclimatic factors. Macroclimate is responsible for the quantity and intensity of precipitation while microclimatic effects modify the quantity of water infiltrating to the rocks. Microclimate affects the development of vegetation, soil temperature and humidity. Millions of microorganisms live in the soil, changing the components of soil-air through the decomposition of organic materials and through their own metabolism. They also influence the physical and chemical soil properties indirectly. The inner dynamism of soil can prevent extreme changes occurring in the system, it can change, possibly leading to disturbance in the whole system. The changes due to external effects are reversible down to the rock boundary. When they have entered the rock layer, they become irreversible. Water in the rock layer is the transport agent of materials and energy. This water reaches the surface again in karst springs. Another irreversible process, the dripstone degradation can also be due to polluted water.
Cayman Brac is a good example of a small oceanic carbonate island which has undergone several periods of submergence and emergence since the Tertiary, resulting in the geological formations being well karstified. This study investigated several karst phenomena on the island including the occurrence and morphology of caves, the water chemistry and microclimate inside the caves, periods of speleothem growth and dissolution, and bell holes. Caves occur throughout the island at various elevations above sea level. Using elevation as a criterion, the caves were divided into Notch caves, located at, or one-two metres above, the Sangamon Notch, and Upper caves, located at varying elevations above the Notch. Analysis of the morphology, age and the relative abundance of speleothem in the caves further supports this division. The close proximity of the Notch and the Notch caves is coincidental: speleothem dating by U-series methods shows that the caves predate the Notch. They are believed to have formed between 1400 and 400 ka, whereas a late Tertiary to Early Quaternary age is assigned to the Upper caves. Speleothem on the island has suffered minor, moderate and major dissolution. Minor dissolution is due to a change in the degree of saturation of the drip water feeding the speleothem, whereas the last two are caused by flooding or condensation corrosion. Many of the speleothems in fact experienced several episodes of dissolution followed by regrowth. The latest episode appears to be caused by condensation corrosion rather than flooding. Eleven speleothems containing growth hiatuses were dated by U-series methods. The results indicate that growth cessation did not occur synchronously. Furthermore, the timing of the hiatuses during the Quaternary is not restricted to glacial or interglacial periods. Oxygen and carbon stable isotope analyses of seven of the samples reveal an apparent shift towards a drier and warmer climate around 120 ka. However, more data and further collaborative evidence is desirable. Of six samples with hiatuses, five show a bi-modal distribution of stable isotope values: before and after the hiatus. Oxygen isotope analyses of modern drip water found inter-sample variations of over 2[per thousand]. This is due to cave environmental factors such as evaporation, infiltration velocity and roof thickness. Inside the caves δ 18 O of drip water decreases with increasing distance from the entrance and thus decreasing external climatic influence. This distance-climatic effect is also reflected in the δ18 O calculated for modern calcite: -5.3, -6.5 and -7.6[per thousand] VPDB at 3, 10 and 20 m respectively. The morphology of bell holes, found only in certain Notch caves, was studied in detail. It is proposed that the bell holes are formed by condensation corrosion, probably enhanced by microbiological activity. The study represents a comprehensive and thorough analyses of karst features on a small oceanic island, and provides information useful for climatic reconstruction during the Quaternary
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