Holocene interaction of maritime and continental climate in Central Europe: New speleothem evidence from Central Germany

Abstract

Central European climate is strongly influenced by North Atlantic (Westerlies) and Siberian High circulation patterns, which govern precipitation and temperature dynamics and induce heterogeneous climatic conditions, with distinct boundaries between climate zones. These climate boundaries are not stationary and shift geographically, depending on long-term atmospheric conditions. So far, little is known about past shifts of these climate boundaries and the local to regional environmental response prior to the instrumental era. High resolution multi-proxy data (stable oxygen and carbon isotope ratios, S/Ca and Sr/Ca) from two Holocene stalagmites from Bleßberg Cave (Thuringia) are used here to differentiate local and pan-regional environmental and climatic conditions Central Germany through the Holocene. Carbon isotope and S/Ca and Sr/Ca ratios inform us on local Holocene environmental changes in and around the cave, while d 18 O (when combined with independent records) serves as proxy for (pan-)regional atmospheric conditions. The stable carbon isotope record suggests repeated changes in vegetation density (open vs. dense forest), and increasing forest cover in the late Holocene. Concurrently, decreasing S/Ca values indicate more effective sulphur retention in better developed soils, with a stabilization in the mid-Holocene. This goes in hand with changes in effective summer infiltration, reflected in the Sr/Ca profile. Highest Sr/Ca values between 4 ka and 1 ka BP indicate intensified prior calcite precipitation resulting from reduced effective moisture supply. The region of Bleßberg Cave is sensitive to shifts of the boundary between maritime (Cfb) and continental (Dfb) climate and ideally suited to reconstruct past meridional shifts of this divide. We combined the Bleßberg Cave d 18 O time series with d 18 O data from Bunker Cave (western Germany) and a North Atlantic Oscillation (NAO) record from lake SS1220 (SW Greenland) to reconstruct the mean position of the Cfb-Dfb climate boundary. We further estimate the dynamic interplay of the North Atlantic Oscillation and the Siberian High and their influence on Central European climate. Repeated shifts of the Cfb-Dfb boundary over the last 4,000 years might explain previously observed discrepancies between proxy records from Europe. Detailed correlation analyses reveal multicentennial scale alternations of maritime and continental climate and, concurrently, waning and waxing influences of Siberian High and NAO on Central Europe.

Pacific climate reflected in Waipuna Cave dripwater hydrochemistry

“…As highlighted in Figure 7,  18 O values vary minimally around a mean dripwater  18 O value of -5.6 ‰, which is only slightly lower than the average rainwater value (-5.15 ‰, Keller 2014). This similarity indicates rapid mixing of freshly infiltrating water with older water in the epikarst, as also found in earlier studies from the Waitomo district (Williams 335 and Fowler, 2002) and elsewhere (Mattey et al, 2008;Tremaine et al, 2016;Breitenbach et al, 2019). The observed buffering of dripwater towards the mean rainwater  18 O value suggests that speleothem  18 O ratios can be expected to reflect (multiannual to multi-decadal changes in rainfall isotope geochemical patterns.…”

Pacific climate reflected in Waipuna Cave drip water hydrochemistry

“…Over the last 2 decades, speleothems have provided invaluable reconstructions of past rainfall, changes in vegetation, and coupled atmosphere-ocean dynamics (Dorale et al, 1998;Asmerom et al, 2010;Myers et al, 2015;Chen et al, 2016;Griffiths et al, 2016;Lechleitner et al, 2017;Kaushal et al, 2018). Speleothems provide reliable continental palaeo-climate records because they allow for modern calibrations linking palaeo-data from stalagmites with meteorological and direct in-cave monitoring, thus making it possible to trace climatic signals from the surface to the speleothem at timescales from seasonal (Frappier et al, 2002) to orbital (Wang et al, 2001(Wang et al, , 2008Meckler et al, 2012;Cheng et al, 2016).…”

Rainfall variations in central Indo-Pacific over the past 2,700 y

“…S3 A ), the observed offsets could be ascribed to different feeding systems for each stalagmite, as in other caves (24–26). Mixing of older and younger waters in the epikarst, and percolation along different flow paths (fracture flow vs. matrix flow), can lead to buffering of the δ 18 O signal: Longer residence time and mixing of water within the overlying rock can both dampen the overall amplitude and lead to offsets between concurrent drip sites (22, 27, 28). If TK131 and TK16 received more fracture flow than TK133, they would be more sensitive to high frequent monsoon event rainfall (with more negative δ 18 O), and less sensitive to mixing with older and/or dry season water.…”