Exploring Holocene Climate Signals Recorded in Stalagmites from Bosnia. A Multi Proxy Approach Coupling Petrography and Geochemistry

Abstract

The Mediterranean area is a densely populated region characterised by an extremely complex atmospheric circulation, which is particularly sensitive to any modification of air mass dynamics. Thus, the understanding of past climate fluctuations in this area is of great importance to gain insight in the pattern of regional climate variability in response to global climate changes. The central Mediterranean area displayed contrasting climatic responses to atmospheric circulation re-organization following the last glacial period: drier/wetter conditions lasted until about 4.5 ka in the northern/southern regions, followed by an opposite trend. To better understand Holocene climate dynamics in the Balkans, a region where only few palaeoclimate reconstructions are available, five stalagmites were collected from two Bosnian caves. Rainfall and cave monitoring was set up in order to understand present day cave hydrology and better interpret the climate and/or environmental signal transfer to the karst. All stalagmites were dated using the U-Th method. Stable carbon and isotope ratios were analysed along the growth axis. Indeed, these values can provide information about temperature, precipitation regime and vegetation cover if calcite is deposited close to isotopic equilibrium conditions. Unfortunately, stable isotope profiles were noisy and not interpretable straightforwardly. Therefore, a multi proxy approach was adopted, coupling stable isotope and trace element profiles with detailed petrographic observations. This allowed for the interpretation of geochemical proxies and petrography variations in relation to hydrological changes. In particular, a trend towards relatively drier conditions appears since about 4 kyr, suggesting a local response to climate change similar to the one of the southern Mediterranean sites. A marginal part of this project involved the examination of a dark lamina deposited around 1.2 ka in the 4 samples from Mracna Pecina cave. This layer, appearing fluorescent under the fluorescence optic microscope, was identified with SEM observation, which demonstrated its soot nature.