Experimental studies at a coastal cave in the Apulian karst, southern Italy

Abstract

<p>Grotta delle Corvine is a submarine cave which opens along the Ionian coast of Apulia (southern Italy), in the spectacular landscape of the Natural Reserve of Porto Selvaggio. The cave takes its name from a species of fish (corvine = <em>Sciaena umbra</em>), which accompanied the cave divers during the first phases of exploration.<em> </em>As concerns its origin, Grotta delle Corvine represents the remaining part of an original karst conduit which development was controlled by the fault systems that shaped the Ionian coastline in the time span from Miocene to Pliocene, and that was later invaded by the sea due to the Mediterranean eustatic movements during the Quaternary. It is definitely the largest among the many submarine caves in the area: with a 8mt-wide and 4mt-high access, opening at -12 m below the sea level, it is widely decorated by speleothems, reaches a total development of some 50 meters, and is characterized by two aerated rooms in its final sector. These latter are two large air sacks, with the widest being over 8mt-large and about 12mt-high, without communication with the outside. The cave hosts a remarkable biodiversity, as testified by a variety of biological studies which documented the presence of 195 species, including 2 new ones. In addition to biology, several other issues are of scientific interest in the cave: these include the “fog effect” related to the wave action and to condensation of the water vapor due to pressure changes, and the presence of cold and hot springs in different sectors of the karst system, among the others.</p><p>Recently, research activities have been started by a group of multi-disciplinary scientists and cavers, aimed at exploring some aspects of scientific interest at Grotta delle Corvine, and at documenting them. In detail, an experiment for measuring the amount of radon in the innermost room of the system has been performed by leaving for 15 days in the cave a measure station with plastic nuclear track detectors (CR39 and Makrofol) in a diffusion chamber. The sensors were dislocated at different heights (from the sea level to 6 mt). Analysis of the CR39 detectors showed uniform radon values over 4000 bequerel/m<sup>3</sup> for all sensors, regardless of the height position. Analysis of the Makrofol sheets, on the other hand, is still ongoing.</p><p>The activities performed so far highlighted the importance of Grotta delle Corvine for many aspects of science: beside the marine biology, already extensively studied but still with a high potential to explore, further geological, hydrogeological and physical investigations are worth to be undertaken at the site. For these reasons, in the next future we plan to continue these experiments aimed at collecting data about the physics of the underground climate, and to add observations and water samplings to define the main hydrogeological characters of the karst system, and to check the main variations in temperature and salinity of the waters, in particular at the two identified springs.</p>