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If you were the great Sherlock Holmes who has been hired for solving a criminal case with no eyewitnesses , what would you do ? Well , if I am not wrong then you ’ ll search for evidence and use your “ Science of Deduction ” to reach the culprit . This collected evidence is called proxies . Proxies are used in other fields as well like Paleoclimatology which is the study of past climates for which no direct measurements are taken . Various geochemical and biological evidence , also known as climate proxies like tree rings , ice sheets , sediment cores , etc . have been used for the paleoclimatic study and in recent decades a new proxy is being studied which is Speleothems . In 2006 , Gideon Henderson , a British Geochemist , had said “ For paleoclimate , the past two decades have been the age of the ice core . The next two may be the age of Speleothem ”.
Nature reflects our nature
Speleothem , derived from Greek words , spleaion : cave and thema : deposit , is a mineral deposit that grows inside a calcareous cave ( made mainly from Calcium Carbonate , CaCO3 ) from dripping ( dripstones ) or flowing ( flowstones ) water . Dripstones that are formed from the roof of caves are called Stalactites whereas the one from the floor is called Stalagmites . Stalagmites have a simple internal structure possessing large scale data , hence they are used to generate the archives of monsoon pattern and its variability .
Two climate parameters i . e . temperature and precipitation affect the infiltration and percolation of soil water which gets into karst aquifer ( formed by dissolution of soluble rocks like limestone and dolomite ) and gets saturated with calcium carbonate , which turns into drip water . It contributes to the formation of speleothems and thus the climate archives get preserved into the speleothem inside a cave . Because very less anthropogenic activity happens inside a cave , the specimens get well preserved for large time-scale . Out of various geochemical proxies like mineralogy ( calcite-aragonite cycle ), trace metals ( Ca / Mg . Mg / Sr ) and biomarkers study ; Uranium ( 234Uranium ) - Thorium ( 230Th ) dating , also known as Thorium-230 dating is mostly done for the determination of the chronology of the Stalagmite specimen , using Thermal Ionization Mass Spectrometry ( TIMS ) and Multi- Collector Inductively Coupled Plasma Mass-Spectrometry ( MC-ICPMS ). This is primarily based on the principle that as the stalagmite grows it integrates Uranium but fails to incorporate Thorium as it is insoluble . The 234Uranium gets converted in 230Th by alpha decay with a half-life of around 245,000 . Then , δ18 O analysis is done , which is a measure of the ratio between 18O species and 16O species . This ratio is dominated by processes like evaporation , mixing , and infiltration of sources of water and hence provides information about the precipitation pattern and variability .
In some recent studies , analysis of biomarkers is also being done to know about the faunal or floral life form present in the various era , in-situ producers , paleoproductivity , etc . Biomarkers or biological markers are molecular fossils that vary in distribution based on the biological source and outside parameters like temperature , pH , and their rate of decomposition . Some of the bio-markers used as proxies are n-alkanes , alcohols , fatty acids , and sterols which are analyzed and identified based on retention time and m / z ratios using Gas Chromatography-Mass spectrometry ( GCMS ). All these multiproxy data are used to conclude about paleoclimate and also for cross-referencing with data from other parts hence adding one more piece to the great climatic puzzle of the world .
If you are wondering whether these Speleothems can be found in Nepal , then the answer is yes . The most famous cave of Pokhara , Mahendra cave is a limestone cave and the dripping water has given rise to various Stalactites as well as Stalagmites . However , due to the flow of thousands of tourists every year the growth has been impeded , hence specimens might not be suitable for study . The good news is that the Pokhara valley has a lot of Karstic caves and many of them are still unexplored with very little human disturbance ( like Krazy cave ).
40 Year Book of Environmental Science