Naslov
Is global warming affecting cave temperatures? Importance for speleothem paleoclimate records

Autori
Domínguez-Villar, David ; Lojen, Sonja ; Krklec, Kristina ; Baker, Andy ; Ian J. Fairchild

Vrsta, podvrsta i kategorija rada
Sažeci sa skupova, sažetak, znanstveni

Izvornik
KR7 Climate Change: The Karst Record. Scientific Programme and Abstracts / Drysdale, R. ; Hellstrom, J. ; Woodhead, J. - Melbourne : Melbourne University Press, 2014, 67-68

Skup
Climate Change: The Karst Record 7th International Conference KR7 "Down Under"

Mjesto i datum
Melbourne, Australija, 29.09.2014. - 03.10.2014

Vrsta sudjelovanja
Predavanje

Vrsta recenzije
Međunarodna recenzija

Ključne riječi
cave temperature ; global warming ; paleoclimate

Sažetak
It is generally accepted that, in most cases, deep sectors of caves have a relatively stable temperature similar to the mean annual temperature outside the cave. Therefore, if there is a link between both, surface and cave atmosphere temperatures, thermal changes at the surface should be recorded underground. However, the processes and response times of the heat transfer are still poorly understood. The period of global warming experienced during the last decades represent an ideal scenario to evaluate the sensitivity of caves to external temperature and the delay in the transfer of the thermal signal. Here we present a 5 year temperature monitoring study of a case study, Postojna Cave, located in Slovenia. This study includes the characterization of the main controls affecting the cave temperature variability in the studied hall and their quantification. A thermal model is implemented for the studied site, where the signal of external atmosphere temperature is transferred underground and the reliability of the model validated with the measured data. The study site was selected for its ideal conditions to evaluate the transfer of external temperature underground. The region has experienced an atmosphere temperature increase of >1.5 ºC since the onset of the 1980s and the vegetation cover over the cave has been maintained for >50 years, not affecting the coupling between atmosphere and ground temperatures. Additionally, the studied cave chamber has a limited advection dynamic allowing the conduction of heat from the ground temperature above the study site to be transferred to the cave by conduction, dominating the low-frequency cave atmosphere temperature. The atmosphere of the studied gallery presents advection processes caused by air density and pressure changes, which provides high frequency and seasonal perturbations. At the depth of the studied gallery (37 m), the drip waters are in equilibrium with the cave bedrock and do not affect cave atmosphere temperature variability. With a limited advection, the changes in temperature seem to be controlled by cave walls temperature. We implemented a thermal conduction model for this chamber that transfers the surface atmosphere temperature of the last decades from the surface to the cave. The results show that the global warming is already being recorded in this particular chamber, although with a delay of 20-25 years. The delay of the thermal signal for a particular depth depends on the duration of the period, and therefore, thermal anomalies with shorter periods have a faster response time in the cave. However, due to the attenuation of the thermal amplitude, periods <5 years are not recorded with a precision of 0.001 ºC. In those caves having their atmosphere temperature dominated y thermal conduction (most of caves’ deep sectors lacking running streams, fast infiltration drainage or very dynamic air advection), the depth of the cave is a critical parameter to determine whether a cave has already recorded the onset of global warming. As temperature affects most of the proxies studied in speleothems, the understood of cave temperature responses to surface atmosphere temperature changes becomes of critical importance since can introduce a significant noise to the interpretation of our proxies or become one of the main controls of the variability of some proxies. The substantial delay between any major thermal change over the cave and its record underground in speleothems is potentially significant for long-term thermal changes. This delay would depend mostly on the depth of the cave, and may introduce a bias in the identification of very precise onset or demise of events recorded in high resolved chronologies. Finally, the changes in cave temperature of one hall in relation to the rest of the cave might be responsible for drastic ventilation dynamics being responsible of changes in growth rate, seasonal deposition and even the occurrence of hiatuses in speleothem records. Given the importance of cave temperature dynamic to understand the detail processes affecting speleothem records, we recommend when presenting a speleothem record, to provide as much information as possible regarding the thermal dynamic of the cave, and specially, to report at least a rough estimation of the depth of the cave, a parameter of critical importance that is frequently omitted from cave environment characterization when reporting speleothem records.

Izvorni jezik
Engleski

Znanstvena područja
Geologija

POVEZANOST RADA