Reconstruction of late Holocene autumn/winter precipitation variability in SW Romania from a high-resolution speleothem trace element record

doi:10.1016/j.epsl.2018.07.027

Earth and Planetary Science Letters

Volume 499, 1 October 2018, Pages 122-133

https://doi.org/10.1016/j.epsl.2018.07.027 Get rights and content

Highlights

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We show a first quantitative autumn/winter precipitation reconstruction from Romania.
•
Precise chronology allows calibration of speleothem record with instrumental data.
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Speleothem Mg/Ca ratios show high anti-correlation with autumn/winter precipitation.
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Our data suggest intermittent weakening of North Atlantic forcing during past 3.6 ka.

Abstract

We present the first high-resolution trace element (Mg/Ca, Sr/Ca, Ba/Ca) record from a stalagmite in southwestern Romania covering the last 3.6 ka, which provides the potential for quantitative climate reconstruction. Precise age control is based on three independent dating methods, in particular for the last 250 yr, where chemical lamina counting is combined with the identification of the 20th century radiocarbon bomb peak and ²³⁰Th/U dating. Long-term cave monitoring and model simulations of drip water and speleothem elemental variability indicate that precipitation-related processes are the main drivers of speleothem Mg/Ca ratios. Calibration against instrumental climate data shows a significant anti-correlation of speleothem Mg/Ca ratios with autumn/winter (October to March) precipitation (r = −0.61, p < 0.01), which is statistically robust when considering age uncertainties and auto-correlation. This relationship is used to develop a quantitative reconstruction of autumn/winter precipitation.

During the late Holocene, our data suggest a heterogeneous pattern of past regional winter hydroclimate in the Carpathian/Balkan realm, along with intermittent weakening of the dominant influence of North Atlantic forcing. In agreement with other regional paleo-hydrological reconstructions, the observed variability reveals periodically occurring strong NW–SE hydro-climate gradients. We hypothesize, that this pattern is caused by shifts of the eastern edge of the area of influence of the NAO across central-eastern Europe due to the confluence of North Atlantic forcing, and other climatic features such as the East Atlantic/Western Russia (EAWR) pattern.

Introduction

Speleothems have been successfully used for quantitative reconstruction of past climate variability (Cai et al., 2010, Jex et al., 2011, Moquet et al., 2016), e.g., using stable oxygen isotope or annual growth lamina records, considered as reliable recorders of air temperature or precipitation amount (Baker and Bradley, 2010, Cai et al., 2010, Tan et al., 2013). Proxy records from laminated stalagmites are best suited for calibration with instrumental data, when lamina-counted chronologies are cross-validated with absolute dating methods (Baker et al., 2007, Smith et al., 2009).

Trace element concentrations constitute additional, valuable tracers of past climate variability (Casteel and Banner, 2015, McDonald et al., 2004, Treble et al., 2003). Mg or Sr co-variability is often linked to hydroclimatic processes via water–rock interaction such as prior calcite precipitation (PCP) or drip rate variability (Cruz et al., 2007, McDonald et al., 2004, Sinclair et al., 2012). However, these processes may be confounded by a variety of second order effects (Fairchild and Treble, 2009, Smith et al., 2009, Treble et al., 2003). Hence, trace element records have so far only sparsely been used for quantitative reconstruction of past precipitation variability, since establishing a transfer function between a climate parameter at the Earths' surface and the speleothem proxy signals requires a rigorous understanding of the processes involved in the proxy signal transfer from the surface into the cave as well as the in-cave processes (Baker and Bradley, 2010, Casteel and Banner, 2015). More recently, the understanding of the drivers of elemental variability in speleothems has greatly improved by model approaches (Sinclair et al., 2012, Stoll et al., 2012), providing a base for calibration studies with speleothem trace elements.

SW Romania is located in a transition region between central Europe, the Mediterranean and western Eurasia. Regional climate is dominated by the influence of the Carpathian mountain topography and westerly driven circulation patterns (Micu et al., 2015). Over southern and eastern Europe, model studies suggest that positive anomalies of both the North Atlantic Oscillation (NAO) and the East Atlantic/Western Russia pattern (EAWR) are associated with negative precipitation anomalies and vice versa (Bojariu and Paliu, 2001, Ionita, 2014).

Precipitation reconstructions from this region providing information on sub-decadal timescales are mainly based on tree-ring data, which are however limited to the growing season and the past several centuries (Levanič et al., 2012, Popa and Kern, 2008). Longer records, which also give insight in past winter climate conditions, can be provided by cave deposits (Cleary et al., 2017, Constantin et al., 2007, Onac et al., 2002, Onac et al., 2014) and lacustrine or peat-bog records (Feurdean et al., 2015, Longman et al., 2017). Many paleo-hydrological reconstructions suggest that the link of Romanian precipitation to North Atlantic climate variability persisted during the Holocene, e.g., Cleary et al. (2017), Longman et al. (2017) or Onac et al. (2002). However, most studies display strong inter-site variability, which is an indication of the complexity of climate in the Romanian Carpathians and in south-eastern Europe (Longman et al., 2017, Roberts et al., 2012). The incongruities in the understanding of the drivers of past precipitation variability in the Carpathian–Balkan region may partly be a consequence of insufficient accuracy and/or scarcity of the available data (Krichak et al., 2014), since many records are often compromised by a rather coarse temporal resolution.

Here we present a first quantitative autumn/winter precipitation reconstruction from SW Romania based on annually resolved speleothem Mg/Ca record. Combined with a precise age control the calibration is based on a comparison with precipitation data and justified by processes derived from drip site and cave air monitoring. Comprehensive statistical analyses confirm the correlation of speleothem Mg/Ca with instrumental data and enable a transfer function to reconstruct the last 3.6 ka. Hence, this precipitation reconstruction allows inferences on spatial and temporal paleo-hydrological variability in the Southern Carpathian realm on up to (multi-) annual timescales.

Section snippets

Sample description

Cloşani Cave (CC, 45.1°N, 22.8°E) is located at the southern slope of the Carpathians in SW Romania at 433 m above sea level (msl) (Fig. 1A and B). The cave is developed in massive Upper Jurassic limestone mainly consisting of calcite (93%) with minor occurrence of dolomite (7%) (Diaconu, 1990). It consists of two main passages with a total length of 1458 m and a vertical range of 15 m (Fig. 1A, Constantin and Lauritzen, 1999). Stalagmite C09-2 was collected in 2009 beneath the active drip site

Monitoring

The seasonal precipitation cycle shows two maxima (Fig. 1C), one in early summer, mainly caused by North Atlantic cyclones, and a second peak in late autumn to early winter (October to December) generated by cyclones from the Mediterranean Basin (Micu et al., 2015). At both meteorological stations, each maximum accounts for approximately 30% of total annual precipitation (1920–1970), respectively. Estimation of potential evapotranspiration (PET, Fig. 1, Fig. 3h) shows that during summer, less

Conclusions

This study is one of the first demonstrating the potential of a speleothem Mg/Ca record for quantitative precipitation reconstruction. We show, that transferring a qualitative measure of coherence allows for a statistical meaningful, first order empirical reconstruction of precipitation. For this purpose, important prerequisites are a very high resolution of a laminated speleothem as well as a sufficient long calibration period.

Hence, despite the presence of dating uncertainties and other

Acknowledgments

This project was funded by the German Science Foundation (DFG grants SCHO 1274/6-1 and SCHO/9-1) and the DFG Research Group 668 (DAPHNE) and also benefited from the support of MC-ICPMS infra-structure through grant DFG-INST 35_1143-1 FUGG. Cave monitoring was supported through the CAVEMONITOR Project (Grant 17SEE/2014) and CARPATHEMS Project (Grant PCE 197/2016) (both to SC). We also acknowledge the data providers in the ECA&D project (Klein Tank et al. (2002), data and metadata available at //www.ecad.eu

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As previously reported, PCP and WRI are two frequently mentioned factors affecting stalagmite trace elements (Johnson et al., 2006; Zhou et al., 2009; Cheng et al., 2016; Owen et al., 2016; Zhao et al., 2017; Li et al., 2021b). It is generally accepted that PCP would increase the X/Ca ratios of drip-water and speleothems because the distribution coefficient of trace element X is usually<1 (McDonald et al., 2004; Cruz Jr et al., 2007; Griffiths et al., 2016; Warken et al., 2018). However, Ca and trace element X would be removed from drip-water with PCP, with a preference of Ca, leading to decrease of their concentration in drip-water and an anti-correlation between trace element X and X/Ca ratio.
Water-rock interaction (WRI) and prior calcite precipitation (PCP) are often employed to interpret the variation in the trace elements present in speleothems and are assumed to be strengthened under drier climates. However, this interpretation is sometimes not consistent with speleothem records in monsoonal China (Zhou et al., 2011; Ban et al., 2018). In this study, a three-year monitoring program was carried out from 2012 to 2014 at Kaiyuan Cave on Shandong Peninsula, coastal North China to investigate how the element geochemistry of drip-water responds to changes in hydroclimate. It was found that trace elements and their ratios to Ca (X/Ca ratio) responded differently to hydroclimatic change at Kaiyuan Cave during the period from 2012 to 2014. Sr and Ba, which are controlled by incongruent dissolution of the host-rock and are sensitive to residence time, show a long-term increasing trend from 2012 to 2014, while Mg and U illustrate a long-term decreasing trend possibly due to reduced dissolution of the host-rock and less input from the soil layer. All the X/Ca ratios are affected by WRI, but the soil layer may have played a role to some extent on the Sr/Ca, Ba/Ca and U/Ca ratios. These findings indicate that trace elements (and X/Ca ratios) of karstic drip-water and speleothems do not respond in the same direction to hydroclimate change as is often suggested in previous publications. Caution is advised when these geochemical proxies are applied to interpret changes in precipitation and/or summer monsoon intensity in China.

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Reconstruction of late Holocene autumn/winter precipitation variability in SW Romania from a high-resolution speleothem trace element record

Highlights

Abstract

Introduction

Section snippets

Sample description

Monitoring

Conclusions

Acknowledgments

Geochim. Cosmochim. Acta

Glob. Planet. Change

Chem. Geol.

Palaeogeogr. Palaeoclimatol. Palaeoecol.

Geochim. Cosmochim. Acta

Quat. Sci. Rev.

Glob. Planet. Change

Geochim. Cosmochim. Acta

Quat. Res.

Earth Planet. Sci. Lett.

Earth Planet. Sci. Lett.

Quat. Sci. Rev.

Glob. Planet. Change

Glob. Planet. Change

Chem. Geol.

Quat. Geochronol.

Quat. Sci. Rev.

Earth Planet. Sci. Lett.

North Atlantic Oscillation projection on Romanian climate fluctuations in the cold season

Effects of intraseasonal variation of summer monsoon rainfall on stable isotope and growth rate of a stalagmite from northwestern Thailand

J. Geophys. Res., Atmos.

Evidence of long-term NAO influence on East-Central Europe winter precipitation from a guano-derived δ15N record

Sci. Rep.

Impacts of the EA and SCA patterns on the European twentieth century NAO-winter climate relationship

Q. J. R. Meteorol. Soc.

Speleothem datings in SW Romania. Part 1: evidence for a continuous speleothem growth in Pestera Closani during oxygen isotope stages 5-3 and its paleoclimatic significance

Theor. Appl. Karstol.

PRYSM: an open-source framework for PRoxY System Modeling, with applications to oxygen-isotope systems

J. Adv. Model. Earth Syst.

Cloşani Cave. Mineralogic and Genetic Study of Carbonate and Clays

Evidence of long-term NAO influence on East-Central Europe winter precipitation from a guano-derived $δ^{15}$ N record