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“Solar Radiation Management” aims to mitigate global warming by either seeding aerosols into clouds to change their radiative properties and occurrence frequency, or injecting sulfur into the atmosphere to shield the Earth’s surface from incoming solar radiation. These approaches are inspired, among other things, by the effect of volcanic eruptions on the climate system.Here we provide a critical reassessment of a time period commonly referred to as the “Medieval Quiet Period”. For several centuries in early Medieval times (c. 750-1050 CE) the climate system was postulated to have been relatively unperturbed by natural climate forcing, resulting in a unique period of climate stability. We present evidence that just the opposite is true. In large parts of the Northern Hemisphere and in the Arctic, atmospheric aerosol loads were persistently high during this period as a result of increased volcanic activity, especially in Iceland.Our new insight is supported by evidence taken from an array of synchronized ice cores from Greenland with high time-resolution records of a large suite of trace elements, including volcanic volatiles such as sulfur, chlorine, fluorine, and heavy metals. We use crypto-tephra in ice cores to provenance the sources of many volcanic eruptions and sulfur isotopes (33S, 34S) to delineate if volcanic gas emissions occurred above or below the ozone layer.We define an “Iceland Active Period”, a time period of frequent and prolonged volcanic activity, producing persistently high levels in atmospheric aerosol burdens in the Northern Hemisphere Arctic’s preindustrial atmosphere lasting for decades to centuries. The frequency and cumulative amount of emissions of climate-impacting trace substances (e.g., sulfates, halogens, ash) is unprecedented in the late Holocene. It is exceeded at times only in the Anthropocene (since about 1900) and in the early-middle Holocene (e.g. during rapid deglaciation). We demonstrate that previous reconstructions of volcanic forcing used in PMIP3 and PMIP4 strongly underestimate volcanic aerosol emissions in the early Medieval and argue that this period should not be considered a reference climate state for the Common Era.Finally, we investigate possible aerosol-climate interactions following these eruptions using climate proxies and state-of-the-art chemistry climate models with prognostic stratospheric aerosols and chemistry.

Volcanic signatures archived in polar ice sheets provide important opportunities to date and correlate ice-core records as well as to investigate the environmental impacts of eruptions. Only the geochemical characterization of volcanic ash (tephra) embedded in the ice strata can confirm the source of the eruption, however, and is a requisite if historical eruption ages are to be used as valid chronological checks on annual ice layer counting. Here we report the investigation of ash particles in a Greenland ice core that are associated with a volcanic sulfuric acid layer previously attributed to the 79 CE eruption of Vesuvius. Major and trace element composition of the particles indicates that the tephra does not derive from Vesuvius but most likely originates from an unidentified eruption in the Aleutian arc. Using ash dispersal modelling, we find that only an eruption large enough to include stratospheric injection is likely to account for the sizeable (24–85 μm) ash particles observed in the Greenland ice at this time. Despite its likely explosivity, this event does not appear to have triggered significant climate perturbations, unlike some other large extra-tropical eruptions. In light of a recent re-evaluation of the Greenland ice-core chronologies, our findings further challenge the previous dating of this volcanic event to 79 CE. We highlight the need for the revised Common Era ice-core chronology to be formally accepted by the wider ice-core and climate modelling communities in order to ensure robust age linkages to precisely dated historical and paleoclimate proxy records.

Far-travelled ash layers from explosive volcanic eruptions can provide invaluable marker horizons for dating and correlating regional to global sedimentary archives. Here, we present a new cryptotephra associated with the ~5.9 cal ka bp Towada-Chuseri eruption (To-Cu) in a peat sediment record from northeast China. This tephra exhibits a rhyolitic glass composition that can be distinguished from other widespread tephra layers around the region of Japan and northeast China. Our findings extend the known range of this ash significantly, making it now traceable about 1200 km from its source, Towada volcano, Japan. Notably, this tephra provides an important isochron for synchronising palaeoenvironmental studies during the mid-Holocene period from the western Pacific, central Japan, Japan Sea and northeast China.

Large regions of Earth's surface are underlain by salt deposits that evaporated from ancient oceans and are populated by extreme halophilic microbes. Some of these halophiles may have been preserved over geological timescales within hypersaline fluid inclusions, but ingresses of water and/or anthropogenic activities can lead to the formation of alternative habitats, including NaCl stalactites or speleothems. While the microbiology of ancient evaporites has been well-studied, the ecology of these recently formed structures is less-well understood. Here, the microbiology of a NaCl stalactite ('salticle') in a Triassic halite mine is characterised. The specific aims were to: determine the presence of fluid inclusions; determine the microbial structure of the salticle compared with a nearby brine-pool and surficial soil; and characterise the ecophysiological capabilities of this unique ecosystem. The salticle contained fluid inclusions, and their microbiome was composed of Euryarchaetota, Proteobacteria, and Actinobacteria, with Haloarchaea in greater abundance than brine-pool or soil microbiomes. The salticle metagenome exhibited a greater abundance of genes involved in osmoregulation, anaerobic respiration, UV resistance, oxidative stress, and stress-protein synthesis relative to the soil microbiome. We discuss the potential astrobiological implications of salticles as enclosed salt-saturated habitats that are protected from ionising radiation and have a stable water-activity. This article is protected by copyright. All rights reserved.

Ice cores are powerful archives for reconstructing volcanism and developing tephrochronological frameworks, as they can preserve both the soluble, i.e. aerosols, and non-soluble, i.e. tephra, products of volcanic eruptions. In addition, and particularly over Holocene timescales, high-precision annually resolved chronologies have been developed for these records and permit ages to be assigned to eruptions. The identification of tephra in ice cores in direct association with chemical indicators of volcanism, such as sulphate, can significantly enhance volcanic reconstructions as tephra can be linked to an eruptive source. Such source attributions can provide information on the location of the eruptions, the magnitude of aerosol emissions at the source and help assess any climatic impact. In addition, they can aid the reconstruction of volcanic histories and the assessment of future hazard risk. The tephra record for the interior of East Antarctica over the last 5,500 years is potentially underexploited as a prior focus on visible horizons and exploring the deep ice cores that cover longer time spans has resulted in only one horizon, dated to ~3.5 ka BP, being identified in these records. Here we discuss ongoing tephrochronological investigations of two ice-cores, B53 and B54, retrieved from the interior of the East Antarctic Plateau. High-resolution, sub-annual chemical records have been measured from both cores using a continuous melter system. These data were used to develop a sampling strategy to identify cryptotephra horizons with ice-core sections containing coeval peaks in fine insoluble particles and non-sea-salt sulphur targeted and >50 events were directly sampled. This approach recently has been used to identify cryptotephras in both Greenland and Antarctic ice cores. When glass tephra shards were identified thin sections were created and individual glass shards were geochemically analysed using electron-probe microanalysis to help identify their volcanic source and permit correlations between records. Thus far, more than 10 cryptotephra horizons have been identified and linked to regional sources such as the South Sandwich and South Shetland Islands and the ~3.5 ka BP event has been traced in both cores as a visible layer. More detailed investigations are being conducted on samples from specific volcanic signals of interest that may derive from eruptions of ultra-distal volcanic sources. Such eruptions could have deposited very small glass tephra shards over Antarctica, which poses significant analytical challenges and necessitates the use of innovative approaches for tephra identification and geochemical analysis.

Tephra layers from explosive eruptions can provide valuable isochronous marker horizons for paleoenvironmental studies across large regions. East Asia and Southeast Asia are host to more than half of the Earth's subaerial volcanoes, and tephras from these volcanoes offer significant numbers of widely distributed marker layers. However, the integrated tephrostratigraphic framework of this region is less refined because only limited (crypto-) tephra sequences have been established. In this study, we present a cryptotephra sequence covering the period ∼60–50 ka in East Asia from a lacustrine sediment from Huguangyan Maar Lake, southern China. Four cryptotephra layers were identified, one of which can be correlated with the ∼53.8 ka Unnan eruption (SUn) of Sambe volcano, Japan. This tephra provides a critical isochronous marker horizon for linking paleoenvironmental records from central Japan to southern China, illustrating a consistent environmental shift during early MIS 3 across this region. The three other tephras cannot be correlated with known eruptions, but glass geochemical compositions suggest that they may be from Japan or surrounding areas, implying that they too may be widely distributed around East Asia. Importantly, two of them feature at the start of MIS 3, and thus can be potentially be used to establish the synchroneity of the onset of MIS 3 around East Asia, overcoming challenges that presently hinder the dating of early MIS 3 in this region.

The Tierra Blanca Joven (TBJ) eruption from Ilopango volcano deposited thick ash over much of El Salvador when it was inhabited by the Maya, and rendered all areas within at least 80 km of the volcano uninhabitable for years to decades after the eruption. Nonetheless, the more widespread environmental and climatic impacts of this large eruption are not well known because the eruption magnitude and date are not well constrained. In this multifaceted study we have resolved the date of the eruption to 431 ± 2 CE by identifying the ash layer in a well-dated, high-resolution Greenland ice-core record that is >7,000 km from Ilopango; and calculated that between 37 and 82 km3 of magma was dispersed from an eruption coignimbrite column that rose to ∼45 km by modeling the deposit thickness using state-of-the-art tephra dispersal methods. Sulfate records from an array of ice cores suggest stratospheric injection of 14 ± 2 Tg S associated with the TBJ eruption, exceeding those of the historic eruption of Pinatubo in 1991. Based on these estimates it is likely that the TBJ eruption produced a cooling of around 0.5 °C for a few years after the eruption. The modeled dispersal and higher sulfate concentrations recorded in Antarctic ice cores imply that the cooling would have been more pronounced in the Southern Hemisphere. The new date confirms the eruption occurred within the Early Classic phase when Maya expanded across Central America., Fieldwork in El Salvador was funded by a grant awarded to G.A.-D. (CONACYT-CB Grant 240447), and we acknowledge logistical support from the following institutions in El Salvador: Ministerio del Medio Ambiente y Recursos Naturales (MARN), Museo Nacional de Arqueología (MUNA), Universidad de El Salvador, and Policía Nacional Civil. V.C.S. and I.S.-P. acknowledge funding from the Natural Environment Research Council (NERC; Grant NE/5009035/1). A.C. acknowledges the Ministero dell’Istruzione dell’Università e della Ricerca project Ash-RESILIENCE. A.S. and M.W.D. acknowledge funding from the European Research Council (ERC) (ECHOES, Grant 714679). M.S. acknowledges funding from the ERC European Union’s Horizon 2020 research and innovation programme (Grant 820047). D.P. acknowledges support from Juan de la Cierva Grant IJCI-2016- 30482. The collection and analysis of the TUNU2013 core was supported by an NSF Division of Polar Programs Grant 1204176 awarded to J.R.M. We thank Walter Hernandez (MARN) and Hugo Díaz Chávez (MUNA) for assistance in the field, Stephen Harris (Department of Plant Sciences, University of Oxford) for identifying the species of the tree that we radiocarbon dated, and Ian Cartwright (School of Archaeology, University of Oxford) for photographing the cross-section of the tree

In Europe, mountain landscapes have evolved in a long‐term relationship with human communities and present‐day landscapes reflect that ancient interaction. The present study aims to reconstruct human activity in twomountain areas in northern Portugal using palynological analysis integrated with the available regional historical,archaeological and palaeo environmental archives. Pollen records from two sedimentary sequences span the Medieval and Modern periods and show that mixed agriculture and livestock grazing were consistently present in both regions throughout these times. Variations in cultural indicators show that the extent of farming fluctuated throughout time, with a general increase in cultivation during the Medieval period but with contractions likely coinciding with times of social disturbance. Historical sources suggest that sociopolitical factors and population pressure were fundamental in the utilisation of upland spaces. This study did not find any convincing evidence to suggest that fire was a fundamental factor in heathland spread. We conclude that long‐term occupation of the uplands was sustained by low‐intensity land use throughout the Medieval to post‐Medieval periods, and that the present landscape has assumed a very different character following depopulation of the mountain areas and a shift towards commercial forestry.© 2020 The Authors. Journal of Quaternary Science Published by John Wiley & Sons Ltd

Highlights • Tephra are abundant in NE North America, with 36 unique units deposited between ∼14,000 and the present day. • Source volcanoes are in the Cascades, Alaska, Kamchatka, Kuriles and potentially Japan. • Updated Bayesian modelled ages are presented for key proximal correlative eruptions and newly described tephra. • The tephra link paleoenvironmental records from this region to the Far East, Greenland and Europe. • Correlated source eruption volumes vary widely; this alone cannot explain recorded ash distribution trends. Lakes and bogs in northeastern North America preserve tephra deposits sourced from multiple volcanic systems in the Northern Hemisphere. However, most studies of these deposits focus on specific Holocene intervals and the latest Pleistocene, providing snapshots rather than a full picture. We combine new data with previous work, supplemented by a broad review of the characteristics and ages of potential source regions and volcanoes, to develop the first composite tephrostratigraphic framework covering the last ∼14,000 years for this region. We report new cryptotephra records from three ombrotrophic peat bogs—Irwin Smith (Michigan), Bloomingdale (New York), and Sidney Bog (Maine)—as well as new analyses and age models from previously reported sites, Nordan's Pond Bog (Newfoundland) and Thin-Ice Pond (Nova Scotia). A new tephra (Iliinsky) from the NGRIP and GRIP ice cores is also presented as it can be correlated to new data from these terrestrial records and helps validate radiocarbon age models. We identify 21 new tephra in addition to the 15 already known, several of which cover the entire region – the White River Ash east, Newberry Pumice, Ruppert (NDN-230), and Mazama. For the first time we find Mount St. Helens Yn (ca. 3660 cal yr BP) and a set P tephra (∼3000–2550 cal yr BP), and confirm the presence of Jala Pumice from Volcan Ceboruco, Mexico, and KS1 from Ksudach volcano, Kamchatka. We describe new “ultra-distal” tephra, including the early Holocene KS2 eruption, and propose correlations to volcanoes Iliinsky and Shiveluch of Kamchatka, and Ushishir of the Kurile Islands. Not all of these tephra represent large eruptions, with several plausible correlations to sub-Plinian events. Using Bayesian age-modeling, we present new age estimates for the newly described tephra, for tephra with previously poor age control, and for several proximal correlatives. Overall, we demonstrate northeastern North America's importance for providing transcontinental linkages between paleoenvironmental records and providing insights into ash distribution from different styles and sizes of eruptions.

New Zealand was among the last habitable places on earth to be colonized by humans1. Charcoal records indicate that wildfires were rare prior to colonization and widespread following the 13th- to 14th-century Māori settlement2, but the precise timing and magnitude of associated biomass-burning emissions are unknown1,3, as are effects on light-absorbing black carbon aerosol concentrations over the pristine Southern Ocean and Antarctica4. Here we used an array of well-dated Antarctic ice-core records to show that while black carbon deposition rates were stable over continental Antarctica during the past two millennia, they were approximately threefold higher over the northern Antarctic Peninsula during the past 700 years. Aerosol modelling5 demonstrates that the observed deposition could result only from increased emissions poleward of 40° S—implicating fires in Tasmania, New Zealand and Patagonia—but only New Zealand palaeofire records indicate coincident increases. Rapid deposition increases started in 1297 (±30 s.d.) in the northern Antarctic Peninsula, consistent with the late 13th-century Māori settlement and New Zealand black carbon emissions of 36 (±21 2 s.d.) Gg y−1 during peak deposition in the 16th century. While charcoal and pollen records suggest earlier, climate-modulated burning in Tasmania and southern Patagonia6,7, deposition in Antarctica shows that black carbon emissions from burning in New Zealand dwarfed other preindustrial emissions in these regions during the past 2,000 years, providing clear evidence of large-scale environmental effects associated with early human activities across the remote Southern Hemisphere. Antarctic ice-core records and atmospheric transport modelling used here show that the 13th-century rise of Māori culture in New Zealand led to a threefold increase of atmospheric black carbon.

New Zealand was among the last habitable places on earth to be colonized by humans

Volcanic ash has been widely used as unique independent marker horizons for dating and synchronizing paleoenvironments and archeological records. Here, we report a series of key widespread late Pleistocene to Holocene tephras horizons from a lake sequence in southern China that have significant potential for dating and synchronizing paleoenvironmental records from East Asia. Translatitudinal paleoclimatological, paleoenvironmental and archeological correlations from the tropical Philippines, mainland China, and mid-latitude Japan are achievable through these extensively distributed tephras, including synthetic studies of the Younger Dryas and mid-Holocene climate events. Additionally, we establish refined ages for four pre-1991 Pinatubo eruptions and date three late Pleistocene Luzon eruptions based on the lake sequence age-model, which will facilitate future studies of tropical volcanic eruptions’ forcing of climate change. Our results highlight the volcanic hazards around densely-populated East Asia, and bring solutions to resolving dating uncertainty in the synchronization of rapid climate events across the region.

Volcanic eruptions are considered as one of the primary natural drivers for changes in the global climate system and understanding the impact of past eruptions on the climate is integral to adopt appropriate responses towards future volcanic eruptions.The Greenland ice core records are dominated by Icelandic eruptions, with several volcanic systems (Katla, Hekla, Bárðarbunga-Veiðivötn and Grimsvötn) being highly active throughout the Holocene. A notable period of increased Icelandic volcanic activity occurred between 500-1250 AD and coincided with climatic changes in the North Atlantic region which may have facilitated the Viking settlement of Greenland and Iceland. However, a number of these volcanic events are poorly constrained (duration and magnitude). Consequently, the Greenland ice cores offer the opportunity to reliably reconstruct past Icelandic volcanism (duration, magnitude and frequency) due to their high-resolution, the proximity of Iceland to Greenland and subsequent increased likelihood of volcanic fallout deposits (tephra particles and sulphur aerosols) being preserved. However, both the high frequency of eruptions between 500-1250 AD and the geochemical similarity of Iceland’s volcanic centres present challenges in making the required robust geochemical correlations between the source volcano and the ice core records and ultimately reliably assessing the climatic-societal impacts of these eruptions.To address this, we use two Greenland ice core records (TUNU2013 and B19) and undertake geochemical analysis on tephra from the volcanic events in the selected time window which have been detected and sampled using novel techniques (insoluble particle peaks and sulphur acidity peaks). Further geochemical analysis of proximal material enables robust correlations to be made between the events in the ice core records and their volcanic centres. The high-resolution of these polar archives provides a precise age for the event and when utilised alongside other proxies (i.e. sulphur aerosols), both the duration and magnitude of these eruptions can be constrained, and the climatic-societal impacts of these eruptions reliably assessed.

We report (1) ice core evidence that unambiguously identifies massive sulfur fallout over much of the Arctic, attributed using tephra geochemistry to eruption of Alaska’s Okmok volcano, with climate model simulations indicating 2 y of extreme temperatures and precipitation throughout the Northern Hemisphere starting in early 43 BCE. This climate event occurred in the waning years of the Roman Republic and Ptolemaic Kingdom during a period of well-known social, political, and economic stress including food shortages, epidemic disease, and unusually inclement weather reported in ancient sources (Fig. 1). We contend that such a climate anomaly—corroborated by paleoclimate proxies—undoubtedly contributed to historical events primarily through disruptions in food production in the Mediterranean region. Without offering any specific criticisms or … [↵][1]1To whom correspondence may be addressed. Email: Joe.McConnell{at}dri.edu. [1]: #xref-corresp-1-1

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 one or more major sulphate emitting volcanic eruptions during the 1450s CE, including the largest atmospheric sulphate loading event in the last 700 years, has not been constrained. Here we explore this issue through a combination of tephrochronological evidence and high-resolution ice-core chemistry measurements from the TUNU2013 ice core. We identify tephra from the historically dated 1477 CE eruption of Veiðivötn-Bárðarbunga, Iceland, in direct association with a notable sulphate peak in TUNU2013 attributed to this event, confirming that it 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 1458/59 CE can be attributed, with a high accuracy, to two notable sulphate peaks. This confirms the accuracy of the NS1-2011 Greenland ice-core chronology over the mid- to late 15th century and corroborate 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 CE and then a Southern Hemisphere eruption, previously assumed to have triggered the cooling, occurred later in 1458 CE. The direct attribution of the 1477 CE sulphate peak to the eruption of Veiðivötn, the most explosive from Iceland in the last 1200 years, also provides the opportunity to assess its climatic impact. A tree-ring based reconstruction of Northern Hemisphere summer temperatures shows a cooling of −0.35 °C in the aftermath of the eruption, the 356th coldest summer since 500 CE, 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, that ranked as the 205th and 9th coldest summers respectively. 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 into more regional palaeoclimatic archives.

Funding: National Science Foundation grants 1925417, 1023672, and 0909541 to J.R.M., and 1824770 to J.G.M. and F.M.L. funded this research, as well as support to A.I.W. and J.R.M. from the John Fell Oxford University Press (OUP) Research Fund and All Souls College, Oxford. Clare Hall, Cambridge provided additional support to J.R.M. through the Sir Nicholas Shackleton fellowship. F.M.L. also acknowledges support from an Irish Research Council Laureate Award (CLICAB project, IRCLA/2017/303). Swiss National Science Foundation grant 18001 funded C.C.R. and W.M.K. European Research Council grant 820047 under the European Union’s Horizon 2020 research and innovation programme supported M.S. A.B. was supported by Marie Curie Career Integration Grant CIG14-631752. The assassination of Julius Caesar in 44 BCE triggered a power struggle that ultimately ended the Roman Republic and, eventually, the Ptolemaic Kingdom, leading to the rise of the Roman Empire. Climate proxies and written documents indicate that this struggle occurred during a period of unusually inclement weather, famine, and disease in the Mediterranean region; historians have previously speculated that a large volcanic eruption of unknown origin was the most likely cause. Here we show using well-dated volcanic fallout records in six Arctic ice cores that one of the largest volcanic eruptions of the past 2,500 y occurred in early 43 BCE, with distinct geochemistry of tephra deposited during the event identifying the Okmok volcano in Alaska as the source. Climate proxy records show that 43 and 42 BCE were among the coldest years of recent millennia in the Northern Hemisphere at the start of one of the coldest decades. Earth system modeling suggests that radiative forcing from this massive, high-latitude eruption led to pronounced changes in hydroclimate, including seasonal temperatures in specific Mediterranean regions as much as 7 °C below normal during the 2 y period following the eruption and unusually wet conditions. While it is difficult to establish direct causal linkages to thinly documented historical events, the wet and very cold conditions from this massive eruption on the opposite side of Earth probably resulted in crop failures, famine, and disease, exacerbating social unrest and contributing to political realignments throughout the Mediterranean region at this critical juncture of Western civilization. Postprint

When considering past human-environment relationships in Ireland, we rarely contemplate the potentially detrimental effects of drought on populations. The summer of 2018 drew attention, however, to some of the ways in which reduced precipitation can impact on societies, even in an oceanic setting such as Ireland. Here, we examine ways in which we can identify the past occurrence of droughts through palaeoenvironmental records. We focus on three time intervals (c. 6200 BC, 3200 BC and 900 BC) for which there is evidence for centennial-scale droughts—drought phases—and consider the available archaeological and palynological records to evaluate whether the droughts may have triggered economic responses or population collapses. We find little evidence to confirm that any of these events undermined the subsistence base to the extent of triggering population collapse. We briefly explore alternative mechanisms by which the drought phases might have impacted upon human perception of their environment.

U. Buntgen received funding from the Ministry of Education, Youth and Sports of CR within the National Sustainability Program I (NPU I; GN LO1415), and additional support was provided by NSF grant 0909541. We are particularly thankful to the NEEM project and its participants.

Professor Emerita Valerie Hall died on 28th July, 2016, in Belfast City Hospital after a long battle with cancer. Valerie was a renowned and highly esteemed inter-disciplinarian, who began her career in botany and palynology but made a truly international mark in the field of cryptotephrochronology. Between us, we knew her as a student, a supervisor, an examiner, a mentor, a colleague, a role model, and, above all, a wonderful, kind-hearted and generous friend. She touched the hearts and earned the respect of Quaternary scientists around the world. Here, to honour her memory, we reflect briefly on the great woman and scientist that she was.

Climate warming and human impacts are thought to be causing peatlands to dry,\ud potentially converting them from sinks to sources of carbon. However, it is unclear\ud whether the hydrological status of peatlands has moved beyond their natural envelope.\ud Here we show that European peatlands have undergone substantial, widespread drying\ud during the last ~300 years. We analyse testate amoeba-derived hydrological\ud reconstructions from 31 peatlands across Britain, Ireland, Scandinavia and continental\ud Europe to examine changes in peatland surface wetness during the last 2000 years.\ud 60% of our study sites were drier during the period CE 1800-2000 than they have been\ud for the last 600 years; 40% of sites were drier than they have been for 1000 years; and\ud 24% of sites were drier than they have been for 2000 years. This marked recent\ud transition in the hydrology of European peatlands is concurrent with compound\ud pressures including climatic drying, warming and direct human impacts on peatlands,\ud although these factors vary between regions and individual sites. Our results suggest\ud that the wetness of many European peatlands may now be moving away from natural\ud baselines. Our findings highlight the need for effective management and restoration of\ud European peatlands.

The dendrochronological potential of short-lived species has had varying degrees of success in the past. Where there has been a level of success with short sequenced assemblages, the focus has been on visual comparisons, based on the occurrence of signature rings. Of vital importance to alder’s ability to be cross-correlated is that it produces a significant amount of distinguishable signature rings. Between 2012 and 2013, a large artificial island (crannog) of medieval date was excavated at Drumclay, County Fermanagh, Northern Ireland, and revealed a site of significant longevity, dating from the 9th century AD to the Post-Medieval period. This excavation exposed a vast number of well-preserved waterlogged archaeological features, resulting in the retention of over 9,000 individual wood samples. Oak timbers were used scarcely in the construction of the crannog, with the dominant wood species identified during excavation being alder. While the oak timbers have proved successful in providing spot dates and indicating phases of activity, the full chronological potential of the wood assemblage lies in the ring patterns of the principal species, alder, particularly with respect to understanding construction phases and site evolution. Previous failures to build chronologies using alder have been attributed to the short-lived and site specific nature of the species. Here, we test whether the measurement of large numbers of samples from a single context within a single site overcomes the limitations posed by alder. We measured the ring-widths of 90 alder samples from archaeological features within the crannog’s infrastructure to test if a robust context chronology could be built. The average ring sequence length ranged from 30 to 60 rings, with one timber extending to 108 rings. Visual correlations were used to aid ring pattern matching in conjunction with statistical correlation. We used radiocarbon wiggle-matching to test the robustness of our constructed chronology and to anchor it to an absolute timescale. Our results to date show that problems of autocorrelation can arise when long alder sequences (>100 rings) are used in conjunction with short sequences (30 to 60 rings). Establishing a rigorous protocol for sample selection has enabled us to develop a more statistically refined methodology that has produced t-values as high as 8.3. We show that in order to construct the best possible alder chronology, multiple ring patterns need to be examined from each context. We recommend examining short-lived assemblages on their own merits; the best approach in these cases is not to look for the longest sequences but instead to focus on the those from the mean sequence range.

To what extent did climate change steer the trajectories of early societies? The final prehistoric (Developed to Late Iron Age) and early medieval periods in Ireland witnessed several major transformations in settlement, economy, material culture and ideology. Here, we review the palaeoenvironmental records to contextualise these transformations in terms of both climate oscillations and land-use history to evaluate whether climate change may have played a role in altering the socio-economic or political framework. We find little evidence that climate change coincided with major cultural alterations in the archaeological record, with pollen records providing important insights into ongoing human activity during times of reduced archaeological visibility. Although palaeoenvironmental records rarely provide sufficient chronological resolution with which to test the effects of abrupt environmental changes on populations, we note no lasting impacts following the proposed downturns that would implicate climate as a determinant of enduring cultural change during these periods.

Plants and animals influence biomass production and nutrient cycling in terrestrial ecosystems; however their relative importance remains unclear. We assessed the extent to which mega-herbivore species controlled plant community composition and nutrient cycling, relative to other factors during and after the Late Quaternary extinction event in Britain and Ireland, when two-thirds of the region’s mega-herbivore species went extinct. Warmer temperatures, plant-soil and plant-plant interactions, and reduced burning contributed to the expansion of woody plants and declining nitrogen availability in our five study ecosystems. Shrub biomass in particular was consistently one of the strongest predictors of ecosystem change, equaling or exceeding the effects of other biotic and abiotic factors. In contrast, there was relatively little evidence for mega-herbivore control on plant community composition and nitrogen availability. The ability of plants to determine the fate of terrestrial ecosystems during periods of global environmental change may therefore be greater than previously thought.

Far-travelled volcanic ash (fine-grained tephra) clouds pose economic and societal risks largely through their potential impact on the aviation industry. A long view of ash clouds extending over northwest Europe assembled from the study and geochemical characterisation of cryptotephra (i.e. tephra invisible to the naked eye) in sedimentary records can help inform the understanding of the frequency of such events, and the nature of eruptions that generate them. Here we review the records of cryptotephra deposition in northwest Europe during the Mid- to Late Holocene (the last eight millennia) to gain insights into the sources of volcanic ash reaching this region. We consider almost 500 published and unpublished datasets for cryptotephras recorded in sedimentary sequences ranging from Ireland to Latvia and, on the basis of their major element geochemical composition, we identify 90 unique ash horizons and their likely provenance. The majority (72%) of the cryptotephras derive from Icelandic eruptions, but a large proportion (24%) originates from other volcanic regions, including Alaska, the Cascades, Kamchatka, Mexico, the Azores and possibly the Mediterranean. Although moderate magnitude eruptions in Iceland may potentially disperse ash clouds over Europe, it appears that only large magnitude events in more distant regions have generally had this capacity and then only when suitable meteorological conditions prevailed. Nevertheless, the cryptotephra records demonstrate that ash clouds from most volcanic regions capable of producing large explosive eruptions in the northern mid- to high latitudes, particularly those to the west of Europe, as well as in tropical North America, have the potential to extend to northwest Europe. Volcanic ash forecasts for this region need therefore to take into account possible risks posed not only by Icelandic eruptions, but also by any large magnitude eruptions in North America or the North Pacific area.

The response of large water-bodies to global change in terms of ecosystem services and economical value is a major concern. The Caspian Sea, the world’s largest enclosed water-body, has a poorly-known water-level history, but observed changes are a hundred times faster than recent global sea-level rise. This ancient lake, characterised by brackish waters, is rich in endemic species; some of them have spread to similar environments worldwide. However, the ecology of Pontocaspian species remains poorly understood and must be studied in their original habitat.This work aims at improving the capacity to reconstruct Quaternary environments of the Pontocaspian region and to provide a benchmark for biodiversity turnover studies. A transect of surface sediment across a wide shelf was subjected to multidisciplinary analyses: stable isotopes, pollen, dinocysts, diatoms, foraminifers, ostracods and molluscs and vertical oceanographic profiles. Three depositional environments with characteristic communities were found: shore face, shelf and slope. Invasion impact was strongly felt by the molluscs. All biota groups, except diatoms, reflected high endemism. The radiocarbon reservoir effect is highlighted in differential 14C ages for different groups. Understanding such discrepancies require detailed insight into reworking processes. Tephra presence in the sediment shows a potential for tephrochronology. Stable isotope ratios in ostracods appear to reflect temperature depth gradients. Our results provide a baseline for calibrating proxy data to the present Pontocaspian environment.

The Greenland Ice Core Chronology 2005 (GICC05) and the radiocarbon calibration curve (IntCal) are the foremost time scales used in paleoclimatic and paleoenvironmental studies of the most recent 10 k.y. Due to varying and often insufficient dating resolution, opportunities to test the synchrony of these two influential chronologies are rare. Here we present evidence for a phase of major pine recruitment on Irish bogs at ca. 8160 yr B.P. Dendrochronological dating of subfossil trees from three sites reveals synchronicity in germination across the study area, indicative of a regional forcing. The concurrent colonization of pine on peatland is interpreted in terms of drier surface conditions and provides the first substantive proxy data in support of a significant hydroclimatic change in the north of Ireland accompanying the 8.2 ka climate cooling event. The date of pine establishment does not overlap with the GICC05 age range for the event, and possible lags between responses are unlikely to explain the full difference. In light of recent studies highlighting a possible offset in GICC05 and IntCal dates, the Irish pine record supports the notion of ice core dates being too early during the period of study. If the suggested discrepancy in timing is an artifact of chronological error, it is likely to have affected interpretations of previous proxy comparisons and alignments.

Volcanic eruptions contribute to climate variability, but quantifying these contributions has been limited by inconsistencies in the timing of atmospheric volcanic aerosol loading determined from ice cores and subsequent cooling from climate proxies such as tree rings. Here we resolve these inconsistencies and show that large eruptions in the tropics and high latitudes were primary drivers of interannual-to-decadal temperature variability in the Northern Hemisphere during the past 2,500 years. Our results are based on new records of atmospheric aerosol loading developed from high-resolution, multi-parameter measurements from an array of Greenland and Antarctic ice cores as well as distinctive age markers to constrain chronologies. Overall, cooling was proportional to the magnitude of volcanic forcing and persisted for up to ten years after some of the largest eruptive episodes. Our revised timescale more firmly implicates volcanic eruptions as catalysts in the major sixth-century pandemics, famines, and socioeconomic disruptions in Eurasia and Mesoamerica while allowing multi-millennium quantification of climate response to volcanic forcing.

Volcanic ash layers preserved within the geologic record represent precise time markers that correlate disparate depositional environments and enable the investigation of synchronous and/or asynchronous behaviors in Earth system and archaeological sciences. However, it is generally assumed that only exceptionally powerful events, such as supereruptions (≥450 km3 of ejecta as dense-rock equivalent; recurrence interval of ~105 yr), distribute ash broadly enough to have an impact on human society, or allow us to address geologic, climatic, and cultural questions on an intercontinental scale. Here we use geochemical, age, and morphological evidence to show that the Alaskan White River Ash (eastern lobe; A.D. 833–850) correlates to the “AD860B” ash (A.D. 846–848) found in Greenland and northern Europe. These occurrences represent the distribution of an ash over 7000 km, linking marine, terrestrial, and ice-core records. Our results indicate that tephra from more moderate-size eruptions, with recurrence intervals of ~100 yr, can have substantially greater distributions than previously thought, with direct implications for volcanic dispersal studies, correlation of widely distributed proxy records, and volcanic hazard assessment.

Major volcanic eruptions can impact on global climate by injecting large quantities of aerosols and ash into the atmosphere that alter the radiative balance and chemical equilibrium of the stratosphere. The Millennium eruption of Tianchi (Paektu), China/North Korea, was one of the largest Late Holocene eruptions. Uncertainty about the precise timing of the eruption has hindered the recognition of its climate impact in palaeoclimate and historical records. Here we report the compelling identification of the eruption's volcanic signal in Greenland ice cores through the association of geochemically characterized volcanic glass, represented in by bimodal populations that compare with proximal material from the source eruption. The eruption most probably occurred in the A.D. 940s, 7 years after the Eldgja eruption on Iceland. We examine the eruption's potential for climate forcing using the sulfate records from the ice cores and conclude that it was unlikely to have had a global or extraregional impact.

Holocene cryptotephras of Alaskan and Pacific Northwestern origin have recently been detected ca. 7000 km away on the east coast of North America. This study extends the emerging North American tephrochronological framework by geochemically characterising seventeen cryptotephra layers from four newly explored peatlands. All detected tephras were deposited during the late Holocene, with no horizons present in the peat between ca. 3000–5000 years ago. The prevalence of the Alaskan White River Ash eastern lobe (AD 847 ± 1) is confirmed across the eastern seaboard from Newfoundland to Maine and a regional depositional pattern from Mount St Helens Set W (AD 1479–1482) is presented. The first occurrences of four additional cryptotephras in eastern North America are described, three of which may originate from source regions in Mexico, Kamchatka (Russia) and Hokkaido (Japan). The possibility of such tephras reaching eastern North America presents the opportunity to link palaeo-archives from the tropics and eastern Asia with those from the western Atlantic seaboard, aiding inter-regional comparisons of proxy-climatic records.

We present distribution maps for all cryptotephras (distal volcanic ash layers) younger than 7 ka that have been reported from three or more lakes or peatlands in north-west Europe. All but one of the tephras originates from Iceland; the exception has been attributed to Jan Mayen. We find strong spatial patterning in tephra occurrence at the landscape scale; most, but not all of the tephra occurrences are significantly spatially clustered, which likely reflects atmospheric and weather patterns at the time of the eruptions. Contrary to expectations based on atmospheric modelling studies, tephras appear to be at least as abundant in Ireland and northern Scotland as in Scandinavia. Rhyolitic and other felsic tephras occur in lakes and peatlands throughout the study region, but andesitic and basaltic tephras are largely restricted to lake sites in the Faroe Islands and Ireland. Explanations of some of these patterns will require further research on the effects of different methodologies for locating and characterizing cryptotephras. These new maps will help to guide future investigations in tephrochronology and volcanic hazard analysis. Postprint

The ash cloud resulting from the A.D. 2010 eruption of Eyjafjallajokull in Iceland caused severe disruption to air travel across Europe, but as a geological event it is not unprecedented. Analysis of peats and lake sediments from northern Europe has revealed the presence of microscopic layers of Icelandic volcanic ash (tephra). These sedimentary records, together with historical records of Holocene ash falls, demonstrate that Icelandic volcanoes have generated substantial ash clouds that reached northern Europe many times. Here we present the first comprehensive compilation of sedimentary and historical records of ash-fall events in northern Europe, spanning the past 7000 yr. Ash-fall events appear to have been more frequent in the past 1500 yr. It is unclear whether this reflects a true increase in eruption frequency or dispersal, or is an artifact of the records or the way in which they have been generated. In the past 1000 yr, volcanic ash clouds reached northern Europe with a mean return interval of 56 ± 9 yr (the range of return intervals is between 6 and 115 yr). Probabilistic modeling using the ash records for the last millennium indicates that for any 10 yr period there is a 16% probability of a tephra fallout event in northern Europe. These values must be considered as conservative estimates due to the nature of tephra capture and preservation in the sedimentary record.

A recently exposed inter-tidal peat bed at Ballywoolen, Bann estuary, Co. Londonderry, has yielded new information about mid-Holocene coastal environmental change in the north-east of Ireland. Pollen analytical data and wood detritus demonstrate that peat accumulation occurred in a terrestrial environment that was free from marine influence. Radiocarbon dates suggest that the peat accumulated rapidly during a period of low relative sea level subsequent to the maximum of Holocene relative sea-level rise along the north coast of Northern Ireland. The absence of marine/brackish indicator taxa at the site suggests that the tidal range was somewhat less than that at present and/or that the channel of the river was located some distance east of its present alignment. The dates indicate that the low stand lasted for at least~0.2 ka and possibly for~1.1 ka. Stable, woodland-dominated landscapes are indicated at both this site and neighbouring ones around~6.4–5.3 cal ka BP. There is no evidence for large-...

The Early Medieval period in Ireland (c. A.D. 400–1150) has been the subject of much archaeological and historical study. The recent application of various forms of archaeological sciences, as well as palaeoenvironmental studies, to the archaeological record have, however, added fresh impetus to this study area. It seems increasingly evident that significant changes to economy and society occurred during this period and were not recorded in detail in the contemporary documentary sources. This paper will attempt to outline those changes and to assess whether, or to what extent, they were influenced by climate change.

We present an analysis of the Northern Irish bog oak record presented in Turney et al. (2005) for the last 4500 years. The record is compared with a compiled peatland water table record from the same region and palaeohydrological data from northern England and mid-latitude Europe. It is apparent that there is no consistent relationship between the population frequency of Irish bog oaks and the palaeohydrological reconstructions, illustrating that the record is not reflecting wetness changes in peatlands. We suggest that the bog oaks should be scrutinised on a within-site and a site-by-site basis to assess the spatial coherency of the shifts in tree populations and the synchronicity of phases of germination and dying off (GDO). Further work is needed to critically examine the controls on the establishment and demise of bog oaks on Irish peatlands before these data can be used as a palaeoclimate proxy. Only then can they be used to test solar forcing of Holocene climate change.

In Ireland, the Middle to Late Bronze Age (1500–600 cal b.c.) is characterised by alternating phases of prolific metalwork production (the Bishopsland and Dowris Phases) and apparent recessions (the Roscommon Phase and the Late Bronze Age-Iron Age transition). In this paper, these changes in material culture are placed in a socio-economic context by examining contemporary settlement and land-use patterns reconstructed from the pollen record. The vegetation histories of six tephrochronologically linked sites are presented, which provide high-resolution and chronologically well-resolved insights into changes in landscape use over the Middle to Late Bronze Age. The records are compared with published pollen records in an attempt to discern if there are trends in woodland clearance and abandonment from which changes in settlement patterns can be inferred. The results suggest that prolific metalworking industries correlate chronologically with expansion of farming activity, which indicates that they were supported by a productive subsistence economy. Conversely, declines in metalwork production occur during periods when farming activity was generally less extensive and perhaps more centralised, and it is proposed that disparate socio-economic or political factors, rather than a collapse of the subsistence economy, lie behind the demise of metalworking industries.

The influence of solar variability on the climate of the Lateglacial and Holocene periods has been the subject of increasing discussion during the last decade. In the Mid-Holocene, several studies have identified cold/wet events that occur at ca 2800 cal. BP and a link with a reduction in solar activity, inferred from the 14C record, has been postulated. We present results from a multi-proxy study of peat humification, plant macrofossils and testate amoebae from a raised bog at Glen West, northwest Ireland, that indicate that dry bog surface conditions were experienced in the north of Ireland at the time of the solar anomaly starting at 2800 cal. BP. With the aid of 14C wiggle-matching and tephrochronology, an abrupt shift to wetter conditions is dated to ca 2700 cal. BP, coinciding with a 14C maximum but clearly post-dating the 2800 cal. BP event identified elsewhere in Europe. We explore the significance of this apparent lag in the Irish record, considering the possible role of the ocean in generating spatial and temporal complexities in the climate patterns of the North Atlantic region. We conclude that these complexities are likely to give rise to time-transgressive climate responses around the North Atlantic that will only be recognised by more critical chronological approaches.

Palaeoecological methods can provide an environmental context for archaeological sites, enabling the nature of past human activity to be explored from an indirect but alternative perspective. Through a palynological study of a small fen peatland located within the catchment of a multi-period prehistoric complex at Ballynahatty, Co. Down, Northern Ireland, we reconstruct the vegetation history of the area during the early prehistoric period. The pollen record reveals tentative evidence for Mesolithic activity in the area at 6410–6220 cal BC, with woodland disturbance identified during the Mesolithic–Neolithic transitional period ca. 4430–3890 cal BC. A more significant impact on the landscape is observed in the Early Neolithic from 3950 to 3700 cal BC, with an opening up of the forest and the establishment of a mixed agricultural economy. This activity precedes and continues to be evident through the Mid-Neolithic during which megalithic tombs and related burial sites were constructed at Ballynahatty. Due to chronological uncertainties and a possible hiatus in peat accumulation in the fen, the contemporary environment of the Ballynahatty timber circle complex (constructed and used ca. 3080–2490 cal BC) and henge (dating to the third millennium cal BC) cannot certainly be established. Nevertheless, the pollen record suggests that the landscape remained open through to the Bronze Age, implying a long continuity of human activity in the area. These findings support the idea that the Ballynahatty prehistoric complex was the product of a gradual and repeated restructuring of the ritual and ceremonial landscape whose significance continued to be recognised throughout the early prehistoric period.

Multiproxy palaeohydrological records from three raised bogs in Northern Ireland indicate that a major shift to wetter/cooler climatic conditions postdated the rapid decrease in solar activity at 2800 cal. BP by ~100 years. This event is bracketed by two wiggle-match radiocarbon-dated cryptotephra layers in each profile, enabling a high degree of chronological precision. These replicated data corroborate previous findings based on Irish peat humification profiles, and may indicate spatial complexity in the climatic response to solar activity between oceanic and continental areas.

A proxy climate record from a raised bog in County Fermanagh, Northern Ireland, is presented. The record spans the interval between 2850 cal. yr BC and cal. yr AD 1000 and chronological control is achieved through the use of tephrochronology and 14C dating, including a wiggle-match on one section of the record. Palaeoclimatic inferences are based on a combination of a testate amoebae-derived water table reconstruction, peat humification and plant macrofossil analyses. This multiproxy approach enables proxy-specific effects to be identified. Major wet shifts are registered in the proxies at ca. 1510 cal. yr BC, 750 cal. yr BC and cal. yr AD 470. Smaller magnitude shifts to wetter conditions are also recorded at ca. 380 cal. yr BC, 150 cal. yr BC, cal. yr AD 180, and cal. yr AD 690. It is hypothesised that the wet shifts are not merely local events as they appear to be linked to wider climate deteriorations in northwest Europe. Harmonic analysis of the proxies illustrates statistically significant periodicities of 580, 423–373, 307 and 265 years that may be related to wider Holocene climate cycles. This paper illustrates how the timing of climate changes registered in peat profiles records can be precisely constrained using tephrochronology to examine possible climatic responses to solar forcing. Relying on interpolated chronologies with considerable dating uncertainty must be avoided if the climatic responses to forcing mechanisms are to be fully understood. Copyright © 2007 John Wiley & Sons, Ltd.