The Potential of Speleothems from Western Europe as Recorders of Regional Climate: A Critical Assessment of the SISAL Database

Abstract

Western Europe is the region with the highest density of published speleothem δ 18 O (δ 18 O spel ) records worldwide. Here, we review these records in light of the recent publication of the Speleothem Isotopes Synthesis and AnaLysis (SISAL) database. We investigate how representative the spatial and temporal distribution of the available records is for climate in Western Europe and review potential sites and strategies for future studies. We show that spatial trends in precipitation δ 18 O are mirrored in the speleothems, providing means to better constrain the factors influencing δ 18 O spel at a specific location. Coherent regional δ 18 O spel trends are found over stadial-interstadial transitions of the last glacial, especially in high altitude Alpine records, where this has been attributed to a strong temperature control of δ 18 O spel . During the Holocene, regional trends are less clearly expressed, due to lower signal-to-noise ratios in δ 18 O spel , but can potentially be extracted with the use of statistical methods. This first assessment highlights the potential of the European region for speleothem palaeoclimate reconstruction, while underpinning the importance of knowing local factors for a correct interpretation of δ 18 O spel . Quaternary 2018, 1, 30 2 of 30and AnaLysis (SISAL) database (SISAL_v1) contains 376 speleothem records from across the globe [3]. About a quarter of these records (92) are from Western Europe, making it the region with the highest density of published speleothem datasets worldwide [3]. This paper reviews these records within the wider (palaeo-)climatic context of Western Europe, with the objective to identify and promote the potential of cave sites in the region for future palaeoclimate studies. Moreover, we test the suitability of a large compilation of speleothem records to reveal the existence of regional trends in space and time [4].While early studies on Western European speleothems principally focused on their availability for temperature reconstruction using δ 18 O of the carbonate [5,6], it was quickly recognised that δ 18 O spel is driven by a complex interplay of regional and site-specific factors, such as moisture source and circulation dynamics, amount of precipitation, dripwater residence time in the overlying karst, cave temperature and ventilation dynamics, and potential kinetic effects during carbonate deposition [7,8]. Due to the filtering effect of the soil-karst system, the δ 18 O spel signal is usually strongly temporally attenuated compared to precipitation δ 18 O, and affected to varying degrees by local noise [4]. This is particularly pronounced at mid-latitude sites and over the Holocene, when ranges in δ 18 O spel are typically small (average standard deviation of Western European δ 18 O spel in SISAL_v1 is 0.36 ) and reflect only moderate climate shifts, as is apparent from other palaeoclimatic evidence (e.g., [9]). Over glacial-interglacial timescales, changes in the seasonality of precipitation and the spatial stationarity of climate patterns need...

Speleothem Records from the Eastern Part of Europe and Turkey—Discussion on Stable Oxygen and Carbon Isotopes

“…In the Holocene, most of the records' δ 13 C values scatter around -10% and do not show any common trend or shift (Figure 3b). Important Holocene climate swings in Europe (e.g., 8.2 and 4.2 ka BP events) have been reported in some speleothem records of European subregions [31,121], however such records are not included in the regional-Eastern Europe and Turkey-subset of the current version of the SISAL_v1 database [30]. Negative δ 13 C anomalies around 3.5 ka BP were recorded in the Sofularand the Trio cave records, which were attributed to regional climate-change events [14].…”

“…The studied region, covering 3.03 × 10 6 km 2 , encompasses East Central Europe, South East Europe and Turkey and is hereafter referred to as the Eastern part of Europe and Turkey. The other parts of continental Europe not considered here are included in a companion paper of this Special Issue [31].…”

“…Whether the δ 18 O spel -elevation gradient ( Figure 6) prevails over geological timescales, especially under distinct climate settings such as the LGM, can be better explored with an increased number of records, providing a much-improved replication in this specific period. The robustness of these empirical gradients can be further explored extending the study region towards nearby regions [31,117].…”

Main controls on the stable carbon isotope composition of speleothems

“…This database was compiled to provide a comprehensive understanding of speleothem δ 18 O and δ 13 C records for climate reconstruction and model evaluation (e.g., Comas-Bru et al, 2019). From this database, several papers have already been published that assess data coverage and investigate regional patterns in stalagmite δ 18 O records from specific regions and continents (e.g., Lechleitner et al, 2018;Oster et al, 2019;Braun et al, 2019;Burstyn et al, 2019). To constrain the governing processes influencing speleothem δ 13 C values in the SISAL records we focus on two subsets of the data of the SISAL_v1 database.…”

SISAL: Bringing Added Value to Speleothem Research

“…Unfortunately, age uncertainties are frequently unreported or omitted in the original publications. This prevented an assessment of the 8.2 ka event in Western Europe where uncertainties were available only for two records ( [42], this issue). Inclusion of age-uncertainty information is particularly worthwhile for older records so that they can be updated using currently standard age-depth model approaches.…”