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Proxies from cave deposits: testing their sensitivity using the current period of global change

Final Report Summary - PROCAVET (Proxies from cave deposits: testing their sensitivity using the current period of global change)

The aim of the Procavet project is to test whether the current global warming and its associated climate effects are causing cave environment modifications, and is being recorded in speleothems over different locations in Europe. After a rigorous survey, five caves located in the United Kingdom, France, Spain and Slovenia were studied. A continuous monitoring program, mainly focused on temperature, was implemented in all caves and the recovery of previous datasets was carried out where available. Additionally, discontinuous monitoring of hydrochemistry of drip waters and cave ventilation processes were conducted in the Spanish and Slovenian caves to better understand those sites.

Stalagmites were recovered from all caves. The samples were annually laminated in most cases which provided a good chronology for extending the record back several decades ago. Chronologies were double checked with hydrochemistry, the recovery of calcite precipitation during those years and by absolute dating by the activity of 14C. Environmental information from stalagmites were obtained using oxygen and carbon stable isotopes, trace elements and growth rates, the latter best recording temperature changes in past decades.

A model in order to understand the heat transfer through the surface to the cave was implemented. This has provided for the first time a clear understanding of the processes governing the transmission of temperature into caves and has provided realistic delay times of the signal that have been able to be double checked by speleothem records and monitoring data.

As the transfer of heat is mainly driven by conduction, the depth of each gallery is crucial in controlling the response in the cave. However, other processes rather than climate change have reported to be of critical importance for understanding changes in cave temperature, as is the case of changes in land use and forest cover.

The results of the project show that caves near the surface can be already recording increases in temperature due to global warming, although delays up to several decades are expected if galleries are some tens of metres in depth. Some stalagmite records have shown already environmental changes suggesting an agreement with the climate change in the surface, whereas others do not show any variability. This is due to the complex processes governing proxies in different locations. That confirms that stalagmites are suitable to record rapid environmental changes, but some delays could be expected in some cases, and that the mechanism affecting the proxies needs to be studied case by case in order to obtain confident results.