Palaeoclimate Archives Research Articles

Mid-Holocene climate at mid-latitudes: assessing the impact of Saharan greening

Abstract. During the first half of the Holocene (11 000 to 5000 years ago), the Northern Hemisphere experienced a strengthening of the monsoonal regime, with climate reconstructions robustly suggesting a greening of the Sahara region. Palaeoclimate archives also show that this so-called African humid period (AHP) was accompanied by changes in climate conditions at middle to high latitudes. However, inconsistencies still exist in reconstructions of the mid-Holocene (MH) climate at mid-latitudes, and model simulations provide limited support in reducing these discrepancies. In this paper, a set of simulations performed using a climate model are used to investigate the hitherto unexplored impact of Saharan greening on mid-latitude atmospheric circulation during the MH. Numerical simulations show Saharan greening has a year-round impact on the main circulation features in the Northern Hemisphere, especially during boreal summer (when the African monsoon develops). Key findings include a westward shift in the global Walker Circulation, leading to modifications in the North Atlantic jet stream in summer and the North Pacific jet stream in winter. Furthermore, Saharan greening modifies atmospheric synoptic circulation over the North Atlantic, enhancing the effect of orbital forcing on the transition of the North Atlantic Oscillation phase from predominantly positive to negative in winter and summer. Although the prescription of vegetation in the Sahara does not improve the proxy–model agreement, this study provides the first constraint on the influence of Saharan greening on northern mid-latitudes, opening new opportunities for understanding MH climate anomalies in regions such as North America and Eurasia.

South Georgia marine productivity over the past 15 ka and implications for glacial evolution

Abstract. The subantarctic islands of South Georgia are located in the Southern Ocean, and they may be sensitive to future climate warming. However, due to a lack of well-dated subantarctic palaeoclimate archives, there is still uncertainty about South Georgia's response to past climate change. Here, we reconstruct primary productivity changes and infer Holocene glacial evolution by analysing two marine gravity cores: one near Cumberland Bay on the inner South Georgia shelf (GC673: ca. 9.5 to 0.3 cal. kyr BP) and one offshore of Royal Bay on the mid-shelf (GC666: ca. 15.2 cal. kyr BP to present). We identify three distinct benthic foraminiferal assemblages characterised by the dominance of Miliammina earlandi, Fursenkoina fusiformis, and Cassidulinoides parkerianus that are considered alongside foraminiferal stable isotopes and the organic carbon and biogenic silica accumulation rates of the host sediment. The M. earlandi assemblage is prevalent during intervals of dissolution in GC666 and reduced productivity in GC673. The F. fusiformis assemblage coincides with enhanced productivity in both cores. Our multiproxy analysis provides evidence that the latest Pleistocene to earliest Holocene (ca. 15.2 to 10.5 cal. kyr BP) was a period of high productivity associated with increased glacial meltwater discharge. The mid–late Holocene (ca. 8 to 1 cal. kyr BP), coinciding with a fall in sedimentation rates and lower productivity, was likely a period of reduced glacial extent but with several short-lived episodes of increased productivity from minor glacial readvances. The latest Holocene (from ca. 1 cal. kyr BP) saw an increase in productivity and glacial advance associated with cooling temperatures and increased precipitation which may have been influenced by changes in the southwesterly winds over South Georgia. We interpret the elevated relative abundance of F. fusiformis as a proxy for increased primary productivity which, at proximal site GC673, was forced by terrestrial runoff associated with the spring–summer melting of glaciers in Cumberland Bay. Our study refines the glacial history of South Georgia and provides a more complete record of mid–late Holocene glacial readvances with robust chronology. Our results suggest that South Georgia glaciers were sensitive to modest climate changes within the Holocene.

Late Quaternary glacial history of the Ulugh Muztagh, central Kunlun Mountains

Only a few studies of Quaternary glaciation have been conducted in the central Kunlun Mountains, hindering a full understanding of Late Pleistocene and Holocene climatic changes on the Tibetan Plateau. This study presents 30 new 10Be surface exposure ages from five moraine crests, two moraine platforms and two glaciofluvial terraces on the northwestern slopes of the Ulugh Muztagh in the central Kunlun Mountains. The moraine ages indicate that an old glacial advance occurred no later than ∼87.10 ka, an extensive glacial advance at ∼35.61 ka and Holocene advances at ∼7.61 ka, ∼1.65 ka, ∼0.69 ka, and ∼ 0.36 ka. Two glaciofluvial terraces were tentatively determined to have been deposited at ∼24.87 ka and ∼ 17.35 ka, possibly implying the occurrence of limited global Last Glacial Maximum (LGM) and Heinrich Stadial 1 glacial advances. After combining these findings with geomorphic evidence, it was inferred that glacial coverage was more extensive during MIS 3 than the global LGM, indicating that the timing of the LGM in the Ulugh Muztagh was asynchronous with that of the monsoon-dominated Tibetan Plateau. Reference to other palaeoclimatic archives suggested that glacial advances since MIS 3 were most likely driven by a combination of cool to cold temperatures and a relatively humid climate. The limited global LGM advance was attributed to increased aridity.

Archaeology, rapid climate changes in the Holocene, and adaptive strategies

The article presents the concepts of repeating cycles of rapid climate variability in the Holocene, including rapid cooling cycles, cold events, ice-rafting events, and rapid climate change recorded in palaeoclimate archives. It also discusses the concepts of adaptation strategies embedded in the catastrophic scenarios of collapse on the one hand, and panarchy, resilience, and adaptation cycle on the other, i.e. the processes of transforming social hierarchical structures into dynamic, adaptive entities. In the rapid climate change series we focus on the 9.2 ka and 8.2 ka climate events associated with the Neolithisation process and the transition to farming. The 5.9 IRD event and/or period of rapid climate change from 6000–5200 cal yr BP are associated with the cultural, economic, and demographic collapse of the Early Neolithic Linear Pottery culture in central and western Europe. We also discuss the triad of recent weakening of North Atlantic ocean circulation, decreased solar activity, and the hypothesised transition to a cold period, the well-known historical scenario associated with the transition to Little Ice Age between 1450 and 1850.

Speleothem growth and stable carbon isotopes as proxies of the presence and thermodynamical state of glaciers compared to modelled glacier evolution in the Alps

In recent years, glacier modelling proved to be an essential tool for simulating Quaternary glacier evolution in the European Alps. Yet, only sparse empirical data mostly concentrated around the Last Glacial Maximum (LGM) is available to validate these simulations. On the other hand, speleothems from the Alps are a widespread palaeoclimate archive. They provide stable carbon isotope records, which can inform about soil and vegetation conditions above a cave site but also potentially about the lack of soil during times of glacier coverage. In addition, speleothem growth in cold, high-elevation cave sites during glacials are a strong indicator of temperatures in the soil-karst-cave system above the freezing point, which is only likely to occur if the cave is covered by a warm-based glacier.Here we use existing speleothem data (growth histories and stable carbon isotopes) from Alpine caves to infer soil coverage (i.e. glacier absence) and thermodynamical states of the glaciers during the last glacial cycle and to statistically assess the compatibility with modelled glacier reconstructions. We compare data from multiple cave sites located at different elevations (870–2512 m a.s.l.) with recent glacier evolution simulations. We find a general agreement between speleothem-derived soil presence or absence and modelled glacier coverage. However, speleothem data provide evidence of surface temperatures above freezing point if covered by a glacier, which is not fully reproduced by the simulations. Our work demonstrates the unique value of speleothem-based reconstructions as proxies to assess the performance of palaeo-ice flow models in a transient manner, whereas only maximum glacier state was considered before due to lack of data.

Modern air, englacial and permafrost temperatures at high altitude on Mt Ortles (3905 m a.s.l.), in the eastern European Alps

Abstract. The climatic response of mountain permafrost and glaciers located in high-elevation mountain areas has major implications for the stability of mountain slopes and related geomorphological hazards, water storage and supply, and preservation of palaeoclimatic archives. Despite a good knowledge of physical processes that govern the climatic response of mountain permafrost and glaciers, there is a lack of observational datasets from summit areas. This represents a crucial gap in knowledge and a serious limit for model-based projections of future behaviour of permafrost and glaciers. A new observational dataset is available for the summit area of Mt Ortles, which is the highest summit of South Tyrol, Italy. This paper presents a series of air, englacial, soil surface and rock wall temperatures collected between 2010 and 2016. Details are provided regarding instrument types and characteristics, field methods, and data quality control and assessment. The obtained data series are available through an open data repository (https://doi.org/10.5281/zenodo.8330289, Carturan et al., 2023). In the observed period, the mean annual air temperature at 3830 m a.s.l. was between −7.8 and −8.6 ∘C. The most shallow layers of snow and firn (down to a depth of about 10 m) froze during winter. However, melt water percolation restored isothermal conditions during the ablation season, and the entire firn layer was found at the melting pressure point. Glacier ice is cold, but only from about 30 m depth. Englacial temperature decreases with depth, reaching a minimum of almost −3 ∘C close to the bedrock, at 75 m depth. A small glacier located at 3470 m a.s.l., close to the summit of Mt Ortles, was also found in cold conditions down to a depth of 9.5 m. The mean annual ground surface temperature was negative for all but one monitored sites, indicating cold ground conditions and the existence of permafrost in nearly all debris-mantled slopes of the summit. Similarly, the mean annual rock wall temperature was negative at most monitored sites, except the lowest one at 3030 m a.s.l. This suggests that the rock faces of the summit are affected by permafrost at all exposures.

Synthesis of stalagmite climatic records in southern China during the last glacial-interglacial cycle

In this study, a 140 kyr stack (MT2022) of 95 stalagmite δ18O records from Southern China was synthesized using the error weighted mean method and the linear weighted mean method. This stack record was derived from approximately 1100 U/Th dating and 40000 δ18O data points. On orbital scale, MT2022 agrees with the variation of the summer (21 July) insolation at 65°N and restores as much detail as possible of the actual variability of Asian Summer Monsoon (ASM) from stalagmite records. The age model of MT2022 was established according to the dating results of each sample record, and the start and end periods of each weak monsoon event were constrained by at least five stalagmite sample records, with average errors of less than 0.2 kyr. By comparison, we find that MT2022 was generally consistent with the Speleothem Interstadial Onset Compilation data set (SIOC19) and had more sample records from the ASM domain, which is more suitable to represent the ASM evolution. Furthermore, comparing MT2022 to three Greenland ice core timescales, we discovered that MT2022 was quite consistent with NGRIP (GICC05) over the last 60 kyr and differed from GRIP (ss09sea) and GISP2 (Meese-Sowers). The main discrepancy between MT2022 and GRIP occurs around Dansgaard-Oeschger (DO) events 14 and 20–23, whereas MT2022 and GISP2 start to deviate prominently beyond 40 kyr BP. The high degree of consistency between GICC05 and MT2022 allows their accuracy to be validated against each other, thus, MT2022 may provide a new chronological reference for climatic events in the last glacial-interglacial cycle as well as an age calibration standard for other palaeoclimate archives.

Using environmental tracers to evaluate the preservation of palaeoclimate signals in aquifers of the London Basin, UK

The concept of aquifer basins as palaeoclimate archives has existed for some decades, yet few detailed studies comparing aquifer types have been carried out. To assess the potential of a particular aquifer as an archive, its hydrogeochemical characteristics must be thoroughly investigated, ideally in comparison to an adjacent aquifer which can be shown to substantially preserve its ice-age endowment at depth. The London Basin (UK) presents such an opportunity, containing two main aquifers of contrasting type: the Chalk, a fractured microporous limestone, and the Lower Greensand, a porous sandstone. Despite intensive exploitation of both, evidence for Devensian (late-glacial) water remains at depth, though this differs between aquifer type. To understand the reasons for this, a suite of environmental tracers has been applied. In addition to hydrochemistry, stable isotopes (δ18O, δ2H), carbon isotopes (δ13C-DIC, 14C-DIC) and noble gases (He, Ne, Ar, Kr and Xe), two tracers new to the basin (CFCs and 14C-DOC) have been used. In effect the Lower Greensand appears to be the ‘reference aquifer’, preserving recharge from prior to the Last Glacial Maximum (LGM), while the Chalk contains mixed water, with no remaining trace of the undiluted pre-LGM end member even at depth in remote parts of the confined basin. Whereas both aquifers had in the past given maximum 14C-DIC model ages ≥ 30kyr (the effective limit of that method), in the present study the use of 14C-DOC has reduced this to 23.4 kyr (Lower Greensand) and 17.2 kyr (Chalk). Similar contrasts in maximum stable isotope depletions (−8.2 ‰ and −7.8 ‰ δ18O) and noble-gas-derived recharge temperature minima (2.6° and 4.1 °C) were also observed. CFCs were found at all Chalk sites, with traces detectable even at 40 km from outcrop, so some climate signal degradation appears inevitable throughout the Chalk aquifer of the basin. A correlation between 14C activity and excess 4He suggests that deep saline water in the Lower Greensand could be ≥ 50kyr old. The use of 14C-DOC in particular appears to be key to understanding how reliable these individual aquifers are as palaeoarchives.

Testing the potential of using coarse-grain feldspars for post-IR IRSL dating of calcium sulphate-wedge growth in the Atacama Desert

The growth of vertically laminated calcium-sulphate wedges in the Atacama Desert is assumed to be driven by the interaction of moisture supply and salt dynamics in the subsurface. Geochronological data of these wedge laminations is yet sparse but indispensable to resolve wedge-growth phases and episodes of moisture supply and to use these deposits as a palaeoclimate archive in the hyperarid environment. Our pilot study presents a first approach of dating a calcium-sulphate wedge from the Atacama Desert using coarse-grain feldspar luminescence dating. Our results show a widespread and clustered equivalent-dose distribution of two wedge samples from ∼20 Gy up to saturation. Optically stimulated luminescence (OSL) of quartz revealed unsuitable properties for dating wedge deposits. Consequently, we applied post-infrared infrared stimulated luminescence (post-IR IRSL) to coarse-grained feldspars. Since feldspar single-grain measurements yielded a low number of luminescent grains, we used 1 mm aliquots as reliable single-grain proxies for genuine single-grain measurements. Data from energy-dispersive x-ray spectroscopy (EDX) showed that the feldspar single grains have large differences in their internal K content, resulting in an averaged internal K content of 3.9 ± 1.0 % for all luminescent grains. This result was subsequently used for dose rate and age calculations. Our results of equivalent-dose distributions and palaeodoses derived from the minimum age model reveal most recent wedge-growth activities at 10.6 ± 2.2 ka and 7.9 ± 1.8 ka for the two wedge samples.

Assessing the robustness of geochronological records from the Arabian Peninsula: A new synthesis of the last 20 ka

The timing and extent of Late Quaternary climate and environmental changes in the Arabian Peninsula were critical for human demographic changes. High resolution palaeoclimate archives suggest that monsoon variability was a key driver of change, but these records obscure environmental heterogeneity at finer spatial scales. Recent decades have seen the production of new, chronometrically controlled records from a range of new sites, with a greater spatial coverage. However, records often appear contradictory vis a vis the hydro-climatic state of the environment and so synthesising them can be challenging. To enhance collation and interpretation of records we have compiled a new database of terrestrial and coastal environmental chronologies for the Arabian Peninsula over the last 20 ka, a key period of marked hydrological change. The SCAPE (Synthesising Chronologies for Arabian PalaeoEnvironments) database contains records that include >700 luminescence and radiocarbon ages. Robustness criteria are applied to identify the utility of each data source in regional hydroclimate reconstruction. The most robust data provide a unique synthesis of 20 ka of palaeoenvironmental change at sub-regional scales. We find that Arabian environmental change does not necessarily follow broad narratives of ‘wet’ or ‘dry’ states but rather the climatic signal is a mosaic of substantial landscape heterogeneity. SCAPE also highlights regions in which more high-quality geochronological investigation is warranted to refine both temporal and spatial records, signifying important avenues for future research.

Early–Middle Pleistocene Magnetostratigraphic and Rock Magnetic Records of the Dolynske Section (Lower Danube, Ukraine) and Their Application to the Correlation of Loess–Palaeosol Sequences in Eastern and South-Eastern Europe

We present new palaeomagnetic and rock magnetic results with a stratigraphic interpretation of the late Early–Middle Pleistocene deposits exposed on the left bank of the River Danube at Dolynske, southern Ukraine. A thick succession of water-lain facies is succeeded by reddish-brown clayey soils, topped by a high-resolution loess–palaeosol sequence. These constitute one of the most complete recently discovered palaeoclimate archives in the Lower Danube Basin. The suggested stratigraphy is based on the position of the Matuyama–Brunhes boundary, rock magnetic, palaeopedological and sedimentological proxies, and it is confidently correlated with other loess records in the region (Roksolany and Kurortne), as well as with the marine isotope stratigraphy. The magnetic susceptibility records and palaeosol characteristics at Dolynske show an outstanding pattern that is transitional between eastern and south-eastern European loess records. Our data confirm that the well-developed S4 soil unit in Ukraine, and S5 units in Romania, Bulgaria and Serbia, correlate with the warm MIS 11. Furthermore, we suggest the correlation of rubified S6 palaeosols in Romania and Bulgaria and the V-S7–V-S8 double palaeosol in Serbia with S6 in Ukraine, a strong Mediterranean-type palaeosol which corresponds to MIS 15. Our new results do not support the hypothesis of a large magnetic lock-in depth like that previously interpreted for the Danube loess, and they prove that the Matuyama–Brunhes boundary is located within the palaeosol unit corresponding to MIS 19. The proposed stratigraphic correlation scheme may serve as a potential basis for further regional and global Pleistocene climatic reconstructions.

The Matuyama—Brunhes boundary in the loess-palaeosol sequence of Dolynske, southern Ukraine

We present the results of a palaeomagnetic study of the Early—Middle Pleistocene deposits exposed on the left bank of the River Danube at Dolynske, southern Ukraine. A thick succession of water-lain facies is succeeded by stratigraphically complete loess-palaeosol sequence; these constitute a unique palaeoclimate archive in the southern margin of the East European loess province. The Matuyama—Brunhes boundary (MBB) has been detected at the bottom of the Lower Shyrokyne (S7S3) subunit and not in the Martonosha (S6) unit as previously thought. New data align with previous results from the Roksolany and Vyazivok sections, where the MBB was determined at the same stratigraphical level in the S7S3 soil. In contrast to terrestrial Pleistocene records in China and сentral Europe, where the MBB was regularly determined in a loess layer (representing a cold period), the MBB in the Ukrainian subaerial succession is located in the soil unit (representing a warm period). Furthermore, eight, and not seven, glacial-interglacial cycles are recorded in the Brunhes chron. This may indicate the stratigraphic completeness of the loess-soil succession of Ukraine, which can be compared with the reference global marine and terrestrial palaeoclimatic archives. Further palaeomagnetic studies of loess-palaeosol sequences of other regions of Ukraine will allow revision and correlation of still inconsistent stratigraphic and magnetostratigraphic schemes of the Pleistocene deposits.

Rainfall variability in southeast and west-central Africa during the Little Ice Age: do documentary and proxy records agree?

Understanding of long-term climatic change prior to instrumental records necessitates reconstructions from documentary and palaeoclimate archives. In southern Africa, documentary-derived chronologies of nineteenth century rainfall variability and palaeoclimate records have permitted new insights into rainfall variability over past centuries. Rarely considered, however, is the climatic information within early colonial documentary records that emerge from the late fifteenth century onwards. This paper examines evidence for (multi-)seasonal dry and wet events within these earlier written records (c. 1550–1830 CE) from southeast Africa (Mozambique) and west-central Africa (Angola) in conjunction with palaeoclimate records from multiple proxies. Specifically, it aims to understand whether these sources agree in their signals of rainfall variability over a 280-year period covering the ‘main phase’ Little Ice Age (LIA) in southern Africa. The two source types generally, but do not always, show agreement within the two regions. This appears to reflect both the nature of rainfall variability and the context behind documentary recording. Both source types indicate that southeast and west-central Africa were distinct regions of rainfall variability over seasonal and longer timescales during the LIA, with southeast Africa being generally drier and west-central Africa generally wetter. However, the documentary records reveal considerable variability within these mean state climatic conditions, with multi-year droughts a recurrent feature in both regions. An analysis of long-term rainfall links with the El Niño–Southern Oscillation (ENSO) in southeast Africa suggests a complex and possibly non-stationary relationship. Overall, early colonial records provide valuable information for constraining hydroclimate variability where palaeoclimate records remain sparse.

Comparing estimation techniques for temporal scaling in palaeoclimate time series

Abstract. Characterizing the variability across timescales is important for understanding the underlying dynamics of the Earth system. It remains challenging to do so from palaeoclimate archives since they are more often than not irregular, and traditional methods for producing timescale-dependent estimates of variability, such as the classical periodogram and the multitaper spectrum, generally require regular time sampling. We have compared those traditional methods using interpolation with interpolation-free methods, namely the Lomb–Scargle periodogram and the first-order Haar structure function. The ability of those methods to produce timescale-dependent estimates of variability when applied to irregular data was evaluated in a comparative framework, using surrogate palaeo-proxy data generated with realistic sampling. The metric we chose to compare them is the scaling exponent, i.e. the linear slope in log-transformed coordinates, since it summarizes the behaviour of the variability across timescales. We found that, for scaling estimates in irregular time series, the interpolation-free methods are to be preferred over the methods requiring interpolation as they allow for the utilization of the information from shorter timescales which are particularly affected by the irregularity. In addition, our results suggest that the Haar structure function is the safer choice of interpolation-free method since the Lomb–Scargle periodogram is unreliable when the underlying process generating the time series is not stationary. Given that we cannot know a priori what kind of scaling behaviour is contained in a palaeoclimate time series, and that it is also possible that this changes as a function of timescale, it is a desirable characteristic for the method to handle both stationary and non-stationary cases alike.

Global calibration of novel 3-hydroxy fatty acid based temperature and pH proxies

3-Hydroxy fatty acids (3-OH-FAs), derived from Gram-negative bacterial outer membranes, have received recent attention for their potential as new terrestrial pH and temperature proxies for palaeoclimate studies. Initial studies from altitudinal transects of contemporary soils – correlating bacterial 3-OH-FA compositions to air temperature and pH – have shown promising results. But the geographical extent of recent calibrations is limited. In this study, we analyse 3-OH-FA lipid distributions in 186 globally distributed soil samples to study the environmental factors controlling the relative distribution of the 3-OH-FA isomers. Our sample-set covers a wide range of temperatures (−0.4 to 27 °C) and pH (3.6–9.2). For the global compilation we find that the ratio of anteiso to normal 3-OH-FAs of the C15 or C17 homologues (RAN15 or RAN17) shows a strong linear relationship with mean annual air temperature (MAAT) (R2 = 0.48, p < 0.001 and R2 = 0.41, p < 0.001, respectively). Additionally, the negative logarithm of the ratio of the summed iso and anteiso to the total amount of normal 3-OH-FAs (RIAN) is also strongly anticorrelated with the soil pH (R2 = 0.66, p < 0.001). However, we find that for our 3-OH-FA based proxies there are significant differences in slope and intercept of the linear corrections at regional scales. Thus local or regional calibrations are likely preferable (at this stage of 3-OH-FA proxy development) for application to specific palaeoclimate archives. We also explore the relationship of 3-OH-FA isomer fractional abundances to environmental parameters using machine learning tool (a Gaussian Process (GP) emulator). This confirms the first order relationships to environmental parameters highlighted by the empirical equations and also derives several alternative GP emulator models for reconstructing MAAT and pH which give higher R2 values (0.66 for MAAT; 0.63 for pH) and lower RSME values (3.5 °C for MAAT; 0.76 for pH) compared to simple linear regressions at the global scale. We compare our 3-OH-FA based indices with bacterial branched glycerol dialkyl glycerol tetraethers (brGDGTs) based indices from the same soil samples. At a global scale RAN15 and RAN17 show negative correlations with the MBT′5ME-MAAT (MBT′5ME, methylation index of 5-methyl branched tetraethers) (r = −0.59, p < 0.001 and r = −0.42, p < 0.001, respectively), whilst RIAN shows strong linear correlations with the cyclisation ratio of branched tetraethers (CBT) (r = 0.77, p < 0.001). Similar to 3-OH-FA based temperature proxies, GDGT based temperature proxy MBT′5ME also showed different regional calibrations. Our new field-based correlations demonstrate the broad physiological response of Gram-negative bacterial cell membranes to external environmental changes on a global scale. We suggest that 3-OH-FA based proxies have widespread potential for palaeoenvironmental studies to estimate past MAAT and soil pH, but that regional/local and context specific calibrations may need to be applied.

Cryptotephra from the Icelandic Veiðivötn 1477 CE eruption in a Greenland ice core: confirming the dating of volcanic events in the 1450s CE and assessing the eruption's climatic impact

Abstract. Volcanic eruptions are a key source of climatic variability, and reconstructing their past impact can improve our understanding of the operation of the climate system and increase the accuracy of future climate projections. Two annually resolved and independently dated palaeoarchives – tree rings and polar ice cores – can be used in tandem to assess the timing, strength and climatic impact of volcanic eruptions over the past ∼ 2500 years. The quantification of post-volcanic climate responses, however, has at times been hampered by differences between simulated and observed temperature responses that raised questions regarding the robustness of the chronologies of both archives. While many chronological mismatches have been resolved, the precise timing and climatic impact of two major sulfate-emitting volcanic eruptions during the 1450s CE, including the largest atmospheric sulfate-loading event in the last 700 years, have not been constrained. Here we explore this issue through a combination of tephrochronological evidence and high-resolution ice-core chemistry measurements from a Greenland ice core, the TUNU2013 record. We identify tephra from the historically dated 1477 CE eruption of the Icelandic Veiðivötn–Bárðarbunga volcanic system in direct association with a notable sulfate peak in TUNU2013 attributed to this event, confirming that this peak can be used as a reliable and precise time marker. Using seasonal cycles in several chemical elements and 1477 CE as a fixed chronological point shows that ages of 1453 CE and 1458 CE can be attributed, with high precision, to the start of two other notable sulfate peaks. This confirms the accuracy of a recent Greenland ice-core chronology over the middle to late 15th century and corroborates the findings of recent volcanic reconstructions from Greenland and Antarctica. Overall, this implies that large-scale Northern Hemisphere climatic cooling affecting tree-ring growth in 1453 CE was caused by a Northern Hemisphere volcanic eruption in 1452 or early 1453 CE, and then a Southern Hemisphere eruption, previously assumed to have triggered the cooling, occurred later in 1457 or 1458 CE. The direct attribution of the 1477 CE sulfate peak to the eruption of Veiðivötn, one of the most explosive from Iceland in the last 1200 years, also provides the opportunity to assess the eruption's climatic impact. A tree-ring-based reconstruction of Northern Hemisphere summer temperatures shows a cooling in the aftermath of the eruption of −0.35 ∘C relative to a 1961–1990 CE reference period and −0.1 ∘C relative to the 30-year period around the event, as well as a relatively weak and spatially incoherent climatic response in comparison to the less explosive but longer-lasting Icelandic Eldgjá 939 CE and Laki 1783 CE eruptions. In addition, the Veiðivötn 1477 CE eruption occurred around the inception of the Little Ice Age and could be used as a chronostratigraphic marker to constrain the phasing and spatial variability of climate changes over this transition if it can be traced in more regional palaeoclimatic archives.

Geomorphic response to the Lateglacial–Holocene transition in high Alpine regions (Sanetsch Pass, Swiss Alps)

Several palaeoclimatic archives have documented the pronounced climatic and environmental change associated with the Lateglacial–Holocene transition in the European Alps. However, the geomorphic response to this major environmental transition has only been punctually investigated. In this study, we propose a detailed reconstruction of post‐Last Glacial Maximum palaeoenvironmental conditions and geomorphic connectivity in the Sanetsch Pass area (2252 m a.s.l., western Swiss Alps) based on a multi‐method approach combining geomorphological and sedimentological field investigations with quantitative sedimentology and geochronology. Samples for sediment characterization (grain size, micromorphology and X‐ray diffraction) and geochronology (optically stimulated luminescence and 10Be surface exposure dating) were collected from three representative landforms of the study area: a high‐elevation silty deposit covered by patterned ground, an alluvial fan, and a hummocky moraine covered by rockfall deposits. Our results reveal the geomorphic history of the three deposits and their connectivity through sediment cascade. These results highlight the development of rapid and most probably transient landscape changes in high Alpine regions during the Lateglacial–Holocene transition, with an increase in sediment flux and the establishment of paraglacial and periglacial geomorphic processes.

Last deglaciation flooding events in the Southern Carpathians as revealed by the study of cave deposits from Muierilor Cave, Romania

Caves often hold valuable palaeoclimate archives including speleothems, fossil remains, and clastic sediments that complement each other. This paper presents a multi-archive interdisciplinary study of an extensive deposit of fossil mammals from the scientific reserve in the Muierilor Cave, Southern Carpathians, Romania. We present two new palaeontological excavations that indicate a high abundance and diversity of MIS 3–2 fossil mammals (carnivores, omnivores and herbivores) synchronous with the early modern humans known from this cave. Using geochronological and sedimentological methods, we present a general reconstruction of the cave evolution between ~120 kyr B.P. and the Holocene. The study is based on a combination of geochronological tools including OSL dating of sediments, U/Th dating of speleothems, and radiocarbon dating of fossil remains, with a total of 54 ages. Based on U/Th dating of speleothems from stratigraphically-relevant positions, we show that the MIS 3 assemblage of fossil mammals were massively reworked and deposited during the post-LGM deglaciation, slightly earlier than previously known for the Southern Carpathians. On the other hand, several young radiocarbon ages of cave bear samples suggest that the Southern Carpathians might have been functioning as a glacial refuge for this species as late as ~22 kyr B.P.

Initial quartz OSL and dust mass accumulation rate investigation of the Kisiljevo loess sequence in north-eastern Serbia

The thick and apparently continuous loess-palaeosol sequences in the Vojvodina region of northern Serbia are recognized and well understood as some of the oldest and most complete terrestrial European palaeoclimatic archives. By contrast, there are few published records for loess profiles from other regions in Serbia. Here we address this knowledge gap by investigating an 8 m thick loess sequence exposed near the village of Kisiljevo in north-eastern Serbia, describing the pedostratigraphy and environmental magnetic signatures in detail and placing these within a chronologic framework using quartz optically stimulated luminescence (OSL) on the 4–11 and 63–90 μm size fractions. Our results show dust accumulation over the last c. 32 ka, with substantial primary loess accumulation during the Early Holocene prior to the formation of the modern soil. We applied two age-depth modelling approaches to estimate dust mass accumulation rates: the Bacon.r software and ADmin model. Both yield high accumulation rates, especially during MIS 2, averaging 550–600 g m−2 a−1 which exceed estimates for other investigated loess sequences in the region.

Rainwater isotopes in central Vietnam controlled by two oceanic moisture sources and rainout effects

The interpretation of palaeoclimate archives based on oxygen isotopes depends critically on a detailed understanding of processes controlling the isotopic composition of precipitation. In the summer monsoonal realm, like Southeast Asia, seasonally and interannually depleted oxygen isotope ratios in precipitation have been linked to the summer monsoon strength. However, in some regions, such as central Vietnam, the majority of precipitation falls outside the summer monsoon period. We investigate processes controlling stable isotopes in precipitation from central Vietnam by combining moisture uptake calculations with monthly stable isotope data observed over five years. We find that the isotopic seasonal cycle in this region is driven by a shift in moisture source from the Indian Ocean to the South China Sea. This shift is reflected in oxygen isotope ratios with low values (− 8 to − 10‰) during summer and high values during spring/winter (0 to − 3‰), while 70% of the annual rainfall occurs during autumn. Interannual changes in precipitation isotopes in central Vietnam are governed by the timing of the seasonal onset and withdrawal of the Intertropical Convergence Zone, which controls the amount of vapour contributed from each source.