engleski

Challenges in monitoring and sampling for the palaeoclimate studies of caves in Zadar region (Croatia)

In July 2012, scientific project Reconstruction of the regional palaeoclimate change – speleothem records from the North Dalmatia (Croatia) started, encompassing 3 caves on the transect from Dalmatian islands to Velebit Mt. peaks: Strašna peć Cave on Dugi otok Island (70 m a.s.l.), Manita peć Cave in Velika Paklenica canyon (Velebit Mt., 570 m a.s.l.) and Spilja u Zubu Buljme Cave (Velebit Mt., 1305 m a.s.l.). The main goal of this study is reconstruction of palaeoenvironmental settings that were recorded in speleothem carbonate, with the intention to assess i) the extent to which climatic conditions in the region varied during the late Quaternary and ii) the likely impact of future climatic changes. The growth history of speleothems within the cave itself offers a first-order palaeoclimate signal, since deposition occurs only when the effective precipitation is sufficient to sustain recharge into the vadose zone. Moreover, in combination with the stable isotope data, palaeoenvironmental changes can be revealed. Stable isotope analyses will be undertaken on sub-samples drilled along the central growth axes of the U- series dated stalagmites to provide a time-series stable isotope record. The first leg of this 3-year project consists exclusively of the field work, monitoring and sampling. Temperature and relative humidity will be monitored for 2 years at the selected sites within all three caves. Four drip- loggers have been installed to record the response of the drip water to the rain events on the surface i.e. to characterize hydrological behavior at the different drip sites, two of which fed the sampled stalagmites. Water samples for stable isotope analyses will be collected monthly for 1 year, as follows: i) rainwater from above the each cave, ii) drip water from each cave, iii) drip water from drip-logger sites in Manita peć Cave. As for the speleothems sampling, two actively growing stalagmites were collected from Manita peć Cave. In spite of relatively simple monitoring and sampling protocol, we encountered several problems caused by natural forces, technical limitations of the equipment and by human interference. Weather conditions such as severe summer drought, autumn precipitation extreme by amount and intensity, and winter snow drifts caused different setbacks, fortunately with no significant damage. Furthermore, at one location very sensitive drip- logger has been threatened by extremely intensive calcification from the drip water, while at two other locations some periods were not recorded because of too big and too small distances between the feeding drip site and the logger. The most evident negative human impact was experienced while collecting the speleothem samples from Manita peć Cave. Namely, in the past when the cave was not protected by the gate almost all of the stalagmites were broken and dislocated. Lately, part of our equipment disappeared probably also because of the irresponsible individuals, in spite of the visible sign of ongoing scientific experiment. In this initial phase of the project, along with collecting samples, a valuable experience was gained, and regardless of few disruptions forthcoming measurements and analyses are expected to be fruitful, offering novel and genuine data and insight into palaeoenvironmental settings of the North Dalmatia.

speleothems; palaeoclimate; palaeoenvironmental changes; Croatia

Projekt 60200 Sveučilišta u Zadru: Rekonstrukcija regionalnih paleoklimatskih promjena – zapisi iz siga sjeverne Dalmacije. Voditeljica: Maša Surić