Noble gas based temperature reconstruction on a Swiss stalagmite from the last glacial–interglacial transition and its comparison with other climate records

Here we present the results of a first application of a “Combined Vacuum Crushing and Sieving (CVCS)” system to determine past (cave/soil) temperatures from dissolved noble gas concentrations in stalagmite samples grown under ‘cold’ climatic conditions (e.g. close to freezing point of water) during the last glacial–interglacial transition. To establish noble gas temperatures (NGTs) also for stalagmites grown in cold regions, we applied the CVCS system to samples from stalagmite M2 precipitated in the Milandre Cave, located in the Swiss Jura Mountains. The investigated stalagmite M2 covers the Allerød–Younger Dryas–Holocene transitions. Noble gas temperatures are determined by using a new algorithm based on noble gas and water abundances and not from concentrations. Noble gas results indicate annual mean temperatures in the Milandre Cave were 2.2±1.8 °C during the late stages of the Allerød, then dropping to 0₍₋₎ ⁺2.6°C at the onset of the Younger Dryas. Such temperatures indicate conditions near to the freezing point of water during the first part of the Younger Dryas. During the last part of the Younger Dryas, the temperature increased to 6.3±2.3 °C. No early Holocene temperature could be determined due the non-detectable water abundances in these samples, however one late Holocene sample indicates a cave temperature of 8.7±2.7 °C which is close to the present day annual mean temperature. NGTs estimated for the Allerød–Younger Dryas–Holocene are in good agreement with paleo-temperature reconstructions from geochemical and biological proxies in lake sediments. The observed deviations between the different paleo-temperature reconstructions are minor if the according temperatures are rescaled to annual mean temperatures and are primarily attributed to the chronological tuning of the different records. As in other stalagmites, NGT reconstructions of the recently precipitated stalagmite (‘young’) samples again are biased, most likely due to diffusive gas loss during sample processing. We speculate that a reduced retentivity of noble gases during experimental sample processing is a general feature of recently precipitated stalagmite fabrics. Therefore, the recently precipitated stalagmite samples do not allow the reliable NGT determination given the currently available experimental methods. Nevertheless, this study makes the case that noble gas thermometry can be applied to stalagmites for paleo-temperature reconstruction based on a physical method including stalagmites that grew during cold climatic conditions.