High‐resolution quantification of earthworm calcite granules from western European loess sequences reveals stadial–interstadial climatic variability during the Last Glacial

Abstract

High concentrations of calcite fossil granules produced by earthworms (ECG) have been identified in most of the stratigraphical units along the loess‐palaeosol reference sequence of Nussloch (Germany). They are particularly abundant in interstadial brown soils and in tundra gley horizons, the latter reflecting short‐term phases of aggradation then degradation of permafrost. These granules are characterized by a radial crystalline structure produced in the earthworms by specific bio‐mineralization processes. In our study, we used this biological indicator combined with 14C and OSL dating, and sedimentological parameters to characterize millennial‐time scale climatic variations recorded in loess sequences. The approach is based on high‐resolution counts of ECG throughout a 17‐m‐thick loess sequence (332 samples). Strong increases in granule and mollusc concentrations suggest warmer climate conditions during palaeosol formation phases, associated with increasing biodiversity, biological activity and vegetation cover. Decreased granule concentrations occur within primary loess deposits, indicating a strong correlation with palaeoenvironmental conditions and demonstrating the reliability of ECG concentration variations as a new palaeoenvironmental proxy. Finally, this pattern is also recorded in loess sequences located about 600 km westward in northern France demonstrating the large‐scale validity of this new palaeoclimatic proxy.

Millennial-timescale quantitative estimates of climate dynamics in central Europe from earthworm calcite granules in loess deposits

“…By taking 15 kg of sediment, we reduce the uncertainties associated with the distribution of ECGs inside one sample of 5 cm thickness. Furthermore, ECG concentration is well correlated with the loess palaeosol pedostratigraphy in Northern France 48 and in the Upper Rhine Valley 49 . Age-depth modelling is based on 28 and 29 radiocarbon analyses for Schwalbenberg and Nussloch, respectively (Supplementary Data 1).…”

“…( 2), ( 3), ( 4) and ( 5). Since earthworms produced ECGs during the active layer thawing season 49 (May to September, the five warmest months of the year; data from Global Terrestrial Network for Permafrost http://gtnpdatabase.org), we propose that the oxygen isotope composition of ECGs records LSTws rather than mean annual land-surface temperature (LST). We reported the distribution of the 30 values for each sample of 5 cm thick at 1σ (Fig.…”

“…Previous studies have demonstrated that the Schwalbenberg 12,72,73 and Nussloch 11,14,29,34,49,74 opportunity to meaningfully investigate terrestrial palaeoclimate change in central Europe over millennial timescales. Our quantitative climatic estimates are derived from in situ ECG response to contemporary conditions at the land surface and are therefore independent of sedimentation rates or direct wind transport vectors.…”

“…We make use of a singular material for quantitative, high resolution palaeoclimate reconstruction from loess sediments, which can be analyzed not only as palaeothermometers 44 and palaeo-rainfall gauges 45 , but can also be directly dated using radiocarbon 11,12 : fossil earthworm calcite granules (ECGs). ECGs are secreted daily at the soil surface 46 by various earthworm species (Lumbricus terrestris being the most productive 47 ), comprise rhombohedral low-Mg calcite crystals which are resistant to diagenetic alteration and experience limited vertical mixing within the loess sediment column 48,49 . The oxygen and carbon isotopic compositions of ECGs provide direct proxies for warmseason land-surface temperature (LSTws) 44 and precipitation 45 .…”

Central Asian Modulation of Northern Hemisphere Moisture Transfer Over the Late Cenozoic

“…This aeolian dust has been transported by air masses associated with the major climate subsystems of the region, chiefly the westerlies 17 , with additional contributions from northerly transport or local katabatic winds 12,18 . Despite the potential of its widespread aeolian deposits 19 to record palaeoclimatic information [20][21][22][23][24] , paleoclimate datasets generated for ACA thus far are either coarse in timescale 17 or focus on recent, short-term intervals insufficient to inform us about long-term feedbacks 13,25 .…”