Description: We present a record of extreme spring–summer runoff events for the past 1600 yr preserved in the varved sediments of Lake Mondsee (Austrian Pre-Alps). Combined sediment microfacies analyses and high-resolution micro-X-ray fluorescence element scanning allow us to identify 157 detrital event layers deposited in spring–summer and to discriminate between regional flood and local debris flow deposits. Higher spring–summer flood activity with a mean event recurrence of 3–5 yr occurred in several well-confined multidecadal episodes during the Dark Ages Cold Period and Medieval time (A.D. 450–480, 590–640, 700–750, and 1140–1170) as well as during the early Little Ice Age (LIA; A.D. 1300–1330 and 1480–1520). In contrast, lowest spring–summer flood activity with an event recurrence of only 30–100 yr is observed during the Medieval Climate Anomaly (A.D. 1180–1300) and the coldest interval of the LIA (A.D. 1600–1700). These findings indicate a complex relationship between temperature conditions and extreme hydro-meteorological events and suggest that enhanced summer Mediterranean cyclogenesis triggers large-scale floods in the northeast Alps during climatic transitions. The Lake Mondsee data demonstrate the climatic sensitivity of spring–summer floods and prove the potential of varved sediment records to investigate the impact of changing climate boundary conditions on seasonal flood activity for pre-instrumental time.

Description: Many studies on ecosystem resilience often lack sufficiently long time scales to determine potential cycles of landscape response. In this paper we review some examples on how palaeoecology has provided an important aid to modern ecology in understanding ecosystem resilience. We focus some of these ideas on two Holocene sites from Southern Spain (Zoñar and Gádor) where current plant diversity is very high. Both sites presented resilient pattern at centennial and millennial time scales with several stable phases. Vegetation in Zoñar proved to be very sensitive to environmental changes, especially moisture availability while forest in Gádor responded elastically to fire and drought to a threshold level when the forest recede to a more open landscape. We conclude that any serious attempt to understand ecosystem resilience should include the long-term perspective.

Description: Solar modulated variations in cosmogenic radionuclide production provide both information on past changes in the activity of the Sun and a global synchronization tool. However, to date the use of cosmogenic radionuclides for these applications is almost exclusively based on 10Be records from ice cores and 14C time-series from tree rings, all including archive-specific limitations. We present the first 10Be record from annually laminated (varved) lake sediments for the Lateglacial-Holocene transition from Meerfelder Maar. We quantify environmental influences on the catchment and, consequently, 10Be deposition using a new approach based on regression analyses between our 10Be record and environmental proxy time-series from the same archive. Our analyses suggest that environmental influences contribute to up to 37% of the variability in our 10Be record, but cannot be the main explanation for major 10Be excursions. Corrected for these environmental influences, our 10Be record is interpreted to dominantly reflect changes in solar modulated cosmogenic radionuclide production. The preservation of a solar production signal in 10Be from varved lake sediments highlights the largely unexplored potential of these archives for solar activity reconstruction, as global synchronization tool and, thus, for more robust paleoclimate studies.

Description: We present new annual sedimentological proxies and sub-annual element scanner data from the Lago Grande di Monticchio (MON) sediment record for the sequence 76–112 thousand years before present (ka). They are combined with the previously published decadal to centennial resolved pollen assemblage in order to provide a comprehensive reconstruction of six major abrupt stadial spells (MON 1–6) in the central Mediterranean during the early phase of the last glaciation. These climatic oscillations are defined by intervals of thicker varves and high Ti-counts and coincide with episodes of forest depletion interpreted as Mediterranean stadial conditions (cold winter/dry summer). Our chronology, labelled as MON-2014, has been updated for the study interval by tephrochronology and repeated and more precise varve counts and is independent from ice-core and speleothem chronologies. The high-resolution Monticchio data then have been compared in detail with the Greenland ice-core δ18O record (NorthGRIP) and the northern Alps speleothem δ18Ocalcite data (NALPS). Based on visual inspection of major changes in the proxy data, MON 2–6 are suggested to correlate with Greenland stadials (GS) 25–20. MON 1 (Woillard event), the first and shortest cooling spell in the Mediterranean after a long phase of stable interglacial conditions, has no counterpart in the Greenland ice core, but coincides with the lowest isotope values at the end of the gradual decrease in δ18Oice in NorthGRIP during the second half of the Greenland interstadial (GI) 25. MON 3 is the least pronounced cold spell and shows gradual transitions, whereas its NorthGRIP counterpart GS 24 is characterized by sharp changes in the isotope records. MON 2 and MON 4 are the longest and most pronounced oscillations in the MON sediments in good agreement with their counterparts identified in the ice and spelethem records. The length of MON 4 (correlating with GS 22) supports the duration of stadial proposed by the NALPS timescales and suggests ca. 500 year longer duration than calculated by the ice-core chronologies GICC05modelext and AICC2012. Absolute dating of the cold spells provided by the MON-2014 chronology shows good agreement among the MON-2014, the GICC05modelext and the NALPS timescales for the period between 112 and 100 ka. In contrast, the MON-2014 varve chronology dates the oscillations MON 4 to MON 6 (92–76 ka) as ca. 3500 years older than the most likely corresponding stadials GS 22 to GS 20 by the other chronologies.

Description: The British Isles lack long high-precision and independent chronologies to reconstruct Holocene environmental and climatic conditions at sub-decadal timescales. This paper reports the first Holocene varved chronology for the lacustrine sediment record of Diss Mere in the UK. The record of Diss Mere is 15 m long, and shows 4.2 m of finely-laminated sediments, which are present between ca. 9 and 13 m of core depth. The microfacies analysis identified three major seasonal patterns of deposition (microfacies 1–3), which corroborate the annual nature of sedimentation throughout the whole interval. The sediments are diatomaceous organic and carbonate varves with an average thickness of 0.45 mm. Microfacies 1 consists of a pale layer of authigenic calcite crystals and diatom frustules, and a dark layer composed of a planktonic diatoms and filaments of organic matter. Microfacies 2 is similar but includes a mono-specific diatom bloom layer preceding the calcite layer. Microfacies 3 consists of varves with an occasional very thin calcite layer and mono-specific diatom blooms in spring and autumn. A total of 8473 varves were counted with maximum counting error of up to 40 varves by the bottom of the varved sequence. To tie the resulting floating varve chronology to the IntCal 2020 radiocarbon timescale, we used a Bayesian Deposition model (P_Sequence with outlier detection) on all available chronological data from the core. The data included five radiocarbon dates, two known tephra layers (Glen Garry and OMH-185) with calendar ages based on Bayesian modelling of sequences of radiocarbon ages, and the relative varve counts between dated points. The resulting age-depth model (DISSV-2020) dates the varved sequence between ca. 2100 and 10,300 cal BP and age uncertainties are decadal in scale (95% confidence). The immediate implication of this new UK Holocene chronology is the updated precise ages for the Glen Garry tephra at 2073 ± 39 cal BP and the OMH-185 tephra at 2617 ± 29 cal BP. DISSV-2020 will also enable Holocene research at high time resolution and comparisons to other annually-resolved records on absolute timescales supporting climatic investigations at the regional level.

Description: We present an early Holocene record from Lake Meerfelder Maar in Germany for in-depth interpretation of depositional changes in annually laminated lake sediments as proxies for climatic and local environmental changes. We characterized the compositional changes in the sediment record using Ward's clustering analyses of the micro X-ray fluorescence core scanning data and linked these to microfacies descriptions. The down-core distribution of the clusters allowed us to define boundaries that represent variations of a comprehensive element assemblage occurring at 11 555, 11 230, 10 650, 10 515 and 9670 varve a BP. Our main results show that during the Early Holocene the long-term vegetation reorganization and evolution of the lake's catchment played a predominant role for sediment deposition. Abrupt shifts occurred at the Younger Dryas/Holocene and the Preboreal/Boreal biostratigraphical boundaries. We do not observe clear signals corresponding to known short-term climatic oscillations described in the North Atlantic region such as the Preboreal Oscillation. A unique and intriguing episode in the history of the lake of predominantly organic deposition and very low amounts of allochthonous sediments occurred between 10 515 and 9670 varve a BP and is related to hydrological thresholds.

Description: The Iberian–Roman Humid Period (IRHP, 2600–1600 cal yr BP), is the most humid phase of the last 4000 yr in southern Spain as recorded in the sedimentary sequence of Zoñar Lake (37°29′00″N, 4°41′22″ W, 300 m a.s. l.). A varve chronology supported by several AMS 14C dates allows study of the lake evolution at annual scale in response to human impact and climate changes. There are four climate phases within this period: i) gradual transition (2600–2500 yr ago, 650–550 BC) from a previous arid period; ii) the most humid interval during the Iberian–Early Roman Epoch (2500–2140 yr ago, 550–190 BC); iii) an arid interval during the Roman Empire Epoch (2140–1800 yr ago, 190 BC AD 150); and iv) a humid period synchronous with the decline of the Roman Empire (1800–1600 yr ago, AD 150–350). Varve thickness and geochemical proxies show a multi-decadal cyclicity similar to modern North Atlantic Oscillation (NAO) (60, 20 years) and solar variability cycles (11 yr). The timing and the structure of this humid period is similar to that described in Eastern Mediterranean and northern European sites and supports the same large-scale climate control for northern latitudes and the Mediterranean region.

Description: Large changes in solar ultraviolet radiation can indirectly affect climate by inducing atmospheric changes. Specifically, it has been suggested that centennial-scale climate variability during the Holocene epoch was controlled by the Sun. However, the amplitude of solar forcing is small when compared with the climatic effects and, without reliable data sets, it is unclear which feedback mechanisms could have amplified the forcing. Here we analyse annually laminated sediments of Lake Meerfelder Maar, Germany, to derive variations in wind strength and the rate of 10Be accumulation, a proxy for solar activity, from 3,300 to 2,000 years before present. We find a sharp increase in windiness and cosmogenic 10Be deposition 2,759  ±  39 varve years before present and a reduction in both entities 199  ±  9 annual layers later. We infer that the atmospheric circulation reacted abruptly and in phase with the solar minimum. A shift in atmospheric circulation in response to changes in solar activity is broadly consistent with atmospheric circulation patterns in long-term climate model simulations, and in reanalysis data that assimilate observations from recent solar minima into a climate model. We conclude that changes in atmospheric circulation amplified the solar signal and caused abrupt climate change about 2,800 years ago, coincident with a grand solar minimum.