Interestingly, the d13C proxy for CO2 levels is also found to be higher during the mid-Holocene Climate Optimum, and between the Roman and Medieval Warm periods in comparison to the end of the record in the mid-20th century. The proxy is obtained from stalagmites and thus reflects CO2 levels present within the cave studied.
The paper adds to over 1000 other peer-reviewed papers finding non-hockey-sticks worldwide.
|Top graph of d18O is a proxy for precipitation and temperature. Bottom graph d13C is a proxy of CO2 levels. Horizontal axis is thousands of years before the present.|
Clim. Past, 10, 1363-1380, 2014
1Emil Racoviţă Institute of Speleology, Romanian Academy, Frumoasă 31, 010986, Bucharest, Romania
2Department of Geology, Babeş-Bolyai University, Kogălniceanu 1, 400084, Cluj-Napoca, Romania
3Institute of Geology and Mineralogy, University of Cologne, Greinstrasse 4–6, 50939, Cologne, Germany
4National Research Centre for Human Evolution, Paseo Sierra de Atapuerca, s/n, 09002 Burgos, Spain
5Department of Geography, Northumbria University, Ellison Building, NE1 8ST, Newcastle upon Tyne, UK
6Department of Earth Sciences, University of Oxford, South Parks Rd, OX1 3AN, Oxford, UK
7School of Geosciences, University of South Florida, 4202 E. Fowler Ave., NES 107, FL 33620, Tampa, USA
8Institute of Speleology, Romanian Academy, Clinicilor 5, 400006, Cluj-Napoca, Romania
Abstract. Here we present a speleothem isotope record (POM2) from Ascunsă Cave (Romania) that provides new data on past climate changes in the Carpathian–Balkan region from 8.2 ka until the present. This paper describes an approach to constrain the effect of temperature changes on calcite δ18O values in stalagmite POM2 over the course of the middle Holocene (6–4 ka), and across the 8.2 and 3.2 ka rapid climate change events. Independent pollen temperature reconstructions are used to this purpose. The approach combines the temperature-dependent isotope fractionation of rain water during condensation and fractionation resulting from calcite precipitation at the given cave temperature. The only prior assumptions are that pollen-derived average annual temperature reflects average cave temperature, and that pollen-derived coldest and warmest month temperatures reflect the range of condensation temperatures of rain above the cave site. This approach constrains a range of values between which speleothem δ18O changes should be found if controlled only by surface temperature variations at the cave site. Deviations of the change in δ18Ocspel values from the calculated temperature-constrained range of change are interpreted towards large-scale variability of climate–hydrology.
Following this approach, we show that an additional ∼0.6‰ enrichment of δ18Oc in the POM2 stalagmite was caused by changing hydrological patterns in SW Romania across the middle Holocene, most likely comprising local evaporation from the soil and an increase in Mediterranean moisture δ18O. Further, by extending the calculations to other speleothem records from around the entire Mediterranean basin, it appears that all eastern Mediterranean speleothems recorded a similar isotopic enrichment due to changing hydrology, whereas all changes recorded in speleothems from the western Mediterranean are fully explained by temperature variation alone. This highlights a different hydrological evolution between the two sides of the Mediterranean.
Our results also demonstrate that during the 8.2 ka event, POM2 stable isotope data essentially fit the temperature-constrained isotopic variability. In the case of the 3.2 ka event, an additional climate-related hydrological factor is more evident. This implies a different rainfall pattern in the Southern Carpathian region during this event at the end of the Bronze Age.