Polar ice cores and historical records evidence a large-magnitude volcanic eruption in 1831 CE. This event was estimated to have injected similar to 13 Tg of sulfur (S) into the stratosphere which produced various atmospheric optical phenomena and led to Northern Hemisphere climate cooling of similar to 1 degrees C. The source of this volcanic event remains enigmatic, though one hypothesis has linked it to a modest phreatomagmatic eruption of Ferdinandea in the Strait of Sicily, which may have emitted additional S through magma-crust interactions with evaporite rocks. Here, we undertake a high-resolution multiproxy geochemical analysis of ice-core archives spanning the 1831 CE volcanic event. S isotopes confirm a major Northern Hemisphere stratospheric eruption but, importantly, rule out significant contributions from external evaporite S. In multiple ice cores, we identify cryptotephra layers of low K andesite-dacite glass shards occurring in summer 1831 CE and immediately prior to the stratospheric S fallout. This tephra matches the chemistry of the youngest Plinian eruption of Zavaritskii, a remote nested caldera on Simushir Island (Kurils). Radiocarbon ages confirm a recent (<300 y) eruption of Zavaritskii, and erupted volume estimates are consistent with a magnitude 5 to 6 event. The reconstructed radiative forcing of Zavaritskii (-2 +/- 1 W m(-2)) is comparable to the 1991 CE Pinatubo eruption and can readily account for the climate cooling in 1831-1833 CE. These data provide compelling evidence that Zavaritskii was the source of the 1831 CE mystery eruption and solve a confounding case of multiple closely spaced observed and unobserved volcanic eruptions.

Geochronological methods provide information on the timing, rates and frequency of environmental processes and events that occur over timescales that exceed laboratory measurements and/or human observation. This chapter discusses the principles of geochronological methods, their applications and limitations.

Volcanic supereruptions are considered among the few drivers of global and existential catastrophes, with recent hypotheses suggesting massive volcanic stratospheric sulfate injection could instigate major shifts in global climate. The absence of supereruptions during recent history as well as large uncertainties on eruption ages limits understanding of the climatic risk they impose. Polar ice cores have well-resolved continuous age models, record past temperature, and contain volcanic sulfate and cryptotephra deposits which can be geochemically fingerprinted to determine eruption timing and improve stratospheric sulfur loading estimates. Here, we provide an age of 79,500 years for the Atitl & aacute;n Los Chocoyos supereruption, one of the largest Quaternary eruptions, by identifying tephra shards in ice cores from both Greenland and Antarctica. This ice core age is supported by a revised marine sediment core stratigraphy age for the Los Chocoyos ash layer. Through comparison with well-dated ice-core temperature proxy records, our study suggests that despite being one of the largest sulfur emissions recorded in ice cores, the Los Chocoyos supereruption did not trigger a millennial-scale cold period.

The 17th century was a period when several major (VEI > 5) tropical and extratropical volcanic eruptions occurred. Amongst these is the VEI 6 eruption of Long Island (Papua New Guinea), which is suggested to have occurred between 1665 and 1668 CE based on historical accounts, radiocarbon dating constraints, and an icecore record from South Pole. Accepting such an attribution on the basis of this ice-core chronology would imply a hitherto undiagnosed dating error of up to 6 years during the 17th century within all ice-core records from Antarctica. Here we constrain the timing of the Long Island eruption through tephrochronology and highresolution glaciochemical measurements from an array of records from Antarctica and Greenland. We identify cryptotephra glass shards in association with the Greenland 1667 CE sulfate peak and geochemically attribute them to the historic Japanese Tarumae (Shikotsu) eruption. This attribution shows that the ice-core records are not misaligned during this period and refines the timing of the Long Island eruption to two candidate dates: 1654 +/- 1 CE and 1662 +/- 1 CE. Both candidate dates are within previous best age estimates based on radiocarbon dating (1651 and 1671 CE, 95.4 % probability). However, here we tentatively use 1662 +/- 1 CE as the timing of the Long Island eruption, as previous radiocarbon constraints suggest a 68.2 % probability of occurrence between 1655 and 1665 CE. With a higher confidence in the dating, we revised volcanic stratospheric sulfur injection (VSSI) estimates across the 17th century. Using these alongside paleo-proxy records, we explored the Northern Hemisphere climate response to the Long Island and Tarumae eruptions and found them to be more limited compared to other major (VEI >5) eruptions during this century. Ultimately, this study has highlighted the accuracy of ice core chronologies, having wider implications for volcanic forcing reconstructions and detection and attribution studies of natural climate variability.

Explosive volcanic eruptions are well known to influence Earth’s temperature. Changes in Earth’s temperature can affect temperature gradients which in turn could affect the isentropic slope and hence Northern Hemisphere high and mid-latitude weather. Yet, the possible influence of volcanic eruptions on these atmospheric circulation patterns and the potential spatial extent are not well understood. To address this issue, we pursue two independent lines of evidence. Firstly, we simulate volcanic eruptions with the MPI-ESM1.2 Earth System Model and use the TRACK algorithm to explore how extra-tropical cyclone (ETC) frequency is affected in the model experiments. Secondly, we query the Greenland ice core NEEM-2011-S1 for indications of increased Northern Hemisphere ETC frequency correlating with evidence for explosive volcanism by comparing the storm proxies sodium and calcium; with the eruption proxy sulphur. Both the model and proxy evidence suggest that large explosive volcanic eruptions increase storminess around the location of the ice core. Furthermore, the simulations indicate that the number of ETCs increases in the subtropics and at high latitudes, while they decrease in the mid-latitudes. A detailed interrogation of the simulated eruptions reveals that increases in cyclone frequency are linked to steepening of the isentropic slope due to a larger meridional temperature gradient and to a lower tropopause. The steepening is driven by a combination of warming of the tropical stratosphere from absorption of longwave radiation by volcanic aerosols and surface cooling due to the scattering of sunlight by the same aerosols, whereas the lower tropopause may be attributed to a warmer stratosphere.

Large volcanic eruptions are key time markers in paleoclimatology because they inject large quantities of volcanic fallout (such as sulfuric acids and tephra) into the atmosphere which is then widely distributed and deposited in environmental archives such as ice cores, lakes and peat bogs. They also produce strong climate effects, imprinted in climate archives such as tree-rings. The caldera-forming eruption of Mount Mazama (Crater Lake, Oregon, USA) some 7700 years ago ranks among the largest eruptions of the Holocene but little is known about its exact timing and global-scale climate impacts. Here we use new high-resolution ice-core analyses of volatiles (S, Cl), particle-size distribution, crypto-tephra and sulfur isotopes (33S, 34S), from ice cores in Greenland and Antarctica, to constrain the date, stratospheric sulfur injection, global aerosol distribution and climate forcing of this eruption. We further demonstrate that the climatic effects left distinctive fingerprints in ultra-long tree-ring chronologies from North America and Europe allowing the date of this eruption to be pinned to a specific year, thereby aligning climate proxy records in North America, Greenland and Europe on a common timeline. Using an ensemble of fully-coupled Earth System Model simulations we identify some key regions experiencing large anomalies in temperature and hydro-climate following the Mt. Mazama eruption. These extreme conditions were not only relevant for hunter-gatherer communities and early agricultural societies emerging in Eurasia, that experienced these compounding effects, but they also help us in identifying a global existential risk arising from comparable eruptions in the future.

Stratospheric sulfate aerosols from explosive volcanic eruptions reflect incoming solar radiation and cool the planet, leading to the hypothesis that the largest volcanic events triggered millennial-scale cold periods over the last ice age. Here, we identify tephra shards from the Atitlán Los Chocoyos supereruption (LCY), one of the largest Quaternary eruptions, in ice cores from Greenland and Antarctica (dated at 79.5 ± 1.7 ka), and a marine sediment core (linked to a sea level highstand at 80.5 ± 0.9 ka). The large ice core sulfate peak associated with the tephra results in an estimated stratospheric sulfur injection of 226 ± 48 Tg S (1σ) for LCY, consistent with volcanic-induced cooling on a multi-annual scale. However, the well-constrained timing of LCY within the high-resolution temperature proxy records of ice cores proves it was not a trigger of millennial-scale cooling.

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.

AbstractExisting global volcanic radiative aerosol forcing estimates portray the period 700 to 1000 as volcanically quiescent, void of major volcanic eruptions. However, this disagrees with proximal Icelandic geological records and regional Greenland ice-core records of sulfate. Here, we use cryptotephra analyses, high-resolution sulfur isotope analyses, and glaciochemical volcanic tracers on an array of Greenland ice cores to characterise volcanic activity and climatically important sulfuric aerosols across the period 700 to 1000. We identify a prolonged episode of volcanic sulfur dioxide emissions (751–940) dominated by Icelandic volcanism, that we term the Icelandic Active Period. This period commences with the Hrafnkatla episode (751–763), which coincided with strong winter cooling anomalies across Europe. This study reveals an important contribution of prolonged volcanic sulfate emissions to the pre-industrial atmospheric aerosol burden, currently not considered in existing forcing estimates, and highlights the need for further research to disentangle their associated climate feedbacks.

&lt;p&gt;Volcanic eruptions are well known to influence Earth&#039;s temperature, however, how eruptions influence the atmosphere&#039;s circulation pattern, especially on the scale of everyday weather is poorly understood. Changing Earth&#039;s temperature can affect temperature gradients which in turn could affect baroclinicity and hence high- and mid-latitude weather. Yet, to what extent volcanic eruptions do in fact exert&amp;#160; such an influence is not clear.&lt;/p&gt; &lt;p&gt;To answer this, we followed two independent lines of investigation: First, we query the Greenland ice-core proxy record for Indications of increased extra-tropical cyclone frequency that correlates with evidence for volcanism. This is done by comparing the storm proxy sea salt (a substance transported to the ice sheet by wind)&amp;#160; with the volcanological proxy sulfur. Secondly, we simulate eruptions with the MPI-ESM1.2 Earth System Model and use the TRACK algorithm to explore how extra-tropical cyclone frequency is affected in the model&amp;#160; experiments. Both approaches suggest that volcanic eruptions impact high- and mid-latitude weather by increasing the number of extra-tropical cyclones especially at higher latitudes. A detailed interrogation of the simulated eruption scenarios suggests that this increase in cyclone frequency is associated with features such as an increase in isentropic slopes and sea-ice extent most commonly found under&amp;#160; colder climate regimes and is the reverse of what one finds in more equable climates such as that projected for the future.&lt;/p&gt;

The Younger Toba Tuff eruption similar to 74 ka ago in Indonesia, is among the largest known supereruptions in the Quaternary and its potential impact on the climate system and human evolution remains controversially debated. The eruption is dated radiometrically to 73.88 +/- 0.32 ka (1s, Storey et al., 2012) and it occurred at the abrupt cooling transition from Greenland Interstadial 20 to Greenland Stadial 20. The precise stratigraphic position of volcanic fallout detected in ice cores from both polar ice sheets has previously been narrowed down to four potential candidates. Here, we compile all available Greenland and Antarctic sulfate records, together with electrical conductivity records and recently obtained sulfur isotope records to identify, quantify and characterize these Toba candidates in terms of their likely latitudinal position of eruption, sulfur emission strength and radiative forcing. We identify that the youngest event of the four candidates is composed of two separate eruptions, both likely located in the extra-tropical Northern Hemisphere. We deem the two older events unlikely candidates for the Toba eruption because of their limited sulfur emission strengths. The second youngest event has the largest sulfur output of the Toba candidates, and it is also larger than any other volcanic event identified in ice core records over the last 60 kyr. Comparable amounts of sulfate deposits in Greenland and Antarctica strongly suggest a tropical source. We thus propose the second youngest event (74,156 years before 2000 CE) to be most likely associated with the Toba eruption. The estimated stratospheric sulfate loading of the proposed Toba eruption is 535 +/- 96 Tg, which is 3 times that of Samalas 1258 CE, 6 times that of Tambora (1815) CE and 20 times that of Pinatubo (1991) CE. We derive the continuous time-series of volcanic sulfate deposition, sulfur emission strength and radiative forcing over the 74.8-73.8 ka time window, suitable for conducting experiments with climate models that either require prescribed forcing field or interactively reproduce aerosol processes. We estimate the cumulative volcanic sulfur emission strength and the radiative forcing of the two younger events and they are found to be much stronger than those at the onset of the Younger Dryas and those preceding the Little Ice Age. Stacked Greenland water isotope records show an accelerated transition trend and abrupt shift after the proposed Toba eruption and suggest that the Greenland moisture source moved southward shortly after the Toba eruption. The Toba eruption may thus have an amplifying effect on the cooling transition leading to Greenland Stadial 20. (c) 2023 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

“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.

Chemical profiles from Greenland ice cores show that the frequency of volcanism was higher during the last glacial-interglacial transition (LGIT) and early Holocene, (17–9 ka b2k) than in any other period during the last 110 kyr. This increased frequency has partly been linked to climate-driven melting of the Icelandic ice sheet during the last deglaciation, with regional isostatic changes thought to alter mantle viscosity and lead to more eruptions. Our study is the first to construct a comprehensive tephrochronological framework from Greenland ice cores over the LGIT to aid in the reconstruction of volcanic activity over this period. The framework is based on extensive high-resolution sampling of three Greenland ice cores between 17.4 and 11.6 ka b2k and comprises a total of 64 cryptotephra deposits from the NGRIP, GRIP and NEEM ice cores. We show that many of these tephras are preserved within the core without an associated chemical signature in the ice, which implies that reconstructions of volcanism based solely on glacio-chemical indicators might underestimate the number of events. Single glass shards from each deposit were geochemically characterised to trace the volcanic source and many of these deposits could be correlated between cores. We show that the 64 deposits represent tephra deposits from 42 separate volcanic events, and of these, 39 are from Iceland, two from the north Pacific region (Japan and USA) and one has an unknown source. Six deposits can be correlated to terrestrial and/or marine tephra deposits in the Northern Hemisphere and the remaining 36 are unreported in other archives. We did not locate tephra from the compositionally distinctive Laacher See eruption (∼13 ka b2k) in our records. Combining our new discoveries with the previously published tephra framework, raises the number of individual tephra horizons found in Greenland ice over this interval to 50. This significantly improves the regional tephrochronological framework, our knowledge of the eruptive history of Iceland during the LGIT and provides new tephra constraints over key LGIT climate events. Consequentially, this framework can guide sampling strategies of future tephra studies in the terrestrial and marine realms aiming to link these records to the Greenland ice cores to assess regional climate synchroneity.

Tephrochronology is a correlational and age-equivalent dating method whereby practitioners characterize, map, and date tephra (or volcanic ash) layers and use them stratigraphically as connecting and dating tools in the geosciences (including volcanology) and in studies of past environments and archaeology. Modern tephra studies per se began around 100 years ago (in the 1920s), but the first collective of tephrochronologists with a common purpose and nascent global outlook was not formed until 7 September 1961 in Warsaw, Poland. On that date, the inaugural “Commission on Tephrochronology” (COT) was ratified under the aegis of the International Union for Quaternary Research (INQUA). The formation of COT is attributable largely to the leadership of Kunio Kobayashi of Japan, the commission's president for its first 12 years. We were motivated to record and evaluate the function and importance of COT because tephrochronology continues to grow globally and its heritage needs to be understood, appreciated, and preserved. In addition, studies on cryptotephras, which are fine-grained glass-shard and/or crystal concentrations preserved in sediments or soils but insufficiently numerous to be visible as a layer to the naked eye, have also expanded dramatically in recent times. Therefore, in this article, we review the role and impacts of COT under the umbrella of INQUA for 53 of the last 60 years or under IAVCEI (International Association of Volcanology and Chemistry of the Earth's Interior) for 7 of the last 60 years, including since 2019. The commission also functioned under other names (abbreviated as COTS, CEV, ICCT, COTAV, SCOTAV, and INTAV; see Table 2 for definitions). As well as identifying key persons of influence, we describe the development of the commission, its leaders, and its activities, which include organizing nine specialist tephra field meetings in seven different countries. Members of the commission have participated in numerous other conferences (including specialist tephra sessions) or workshops of regional to international scale, and they have played leading roles in international projects such as INTIMATE (INTegrating Ice-core, MArine and TErrestrial records) and SMART (Synchronising Marine And ice-core Records using Tephrochronology). As well as strongly supporting early-career researchers including graduate students, the commission has generated 10 tephra-themed journal volumes and two books. It has published numerous other articles including field guidebooks, reports, and specialist internet documents/sites. Although its fortunes have ebbed as well as flowed, the commission began to prosper after 1987 when key changes in leadership occurred. COT has blossomed further, especially in the past decade or so, as an entire new cohort of specialists, including many engaged in cryptotephra studies, has emerged alongside new geoanalytical and dating techniques or protocols to become a vibrant global group today. We name 29 elected officers who have been involved with COT since 1961 as well as 15 honorary life members. After reviewing the aims of the commission, we conclude by evaluating its legacies and by documenting current and future work.

Tephra is a unique volcanic product with an unparalleled role in understanding past eruptions, long-term behavior of volcanoes, and the effects of volcanism on climate and the environment. Tephra deposits also provide spatially widespread, high-resolution time-stratigraphic markers across a range of sedimentary settings and thus are used in numerous disciplines (e.g., volcanology, climate science, archaeology). Nonetheless, the study of tephra deposits is challenged by a lack of standardization that inhibits data integration across geographic regions and disciplines. We present comprehensive recommendations for tephra data gathering and reporting that were developed by the tephra science community to guide future investigators and to ensure that sufficient data are gathered for interoperability. Recommendations include standardized field and laboratory data collection, reporting and correlation guidance. These are organized as tabulated lists of key metadata with their definition and purpose. They are system independent and usable for template, tool, and database development. This standardized framework promotes consistent documentation and archiving, fosters interdisciplinary communication, and improves effectiveness of data sharing among diverse communities of researchers.

Abstract. Modern tephra studies per se began almost 100 years ago (in the late 1920s) but the first collective of tephrochronologists, with a common purpose and nascent global outlook, was not formed until 7 September, 1961, in Warsaw, Poland. On that date, the inaugural ‘Commission on Tephrochronology’ (COT) was ratified under the aegis of the International Union for Quaternary Research (INQUA). COT’s formation can be attributed largely to the leadership of Kunio Kobayashi of Japan, the commission’s president for its first 12 years. We were motivated to record COT’s heritage for posterity and also because the discipline of tephrochronology, including the study of cryptotephras, continues to grow globally at a significant rate. This is recognition of tephrochronology as both a unique correlational and age-equivalent dating method, and as a complementary method in other fields, such as volcanology, in which tephra research has been employed to develop eruption histories and hazards and to help understand volcano-climate interactions. In this article, we review the history of COT (which also functioned under other names, abbreviated as COTS, CEV, ICCT, COTAV, SCOTAV, INTAV) under the umbrella of INQUA for 53 of the last 60 years, or under IAVCEI (International Association of Volcanology and Chemistry of the Earth’s Interior) for seven of the last 60 years, including since 2019. We describe the development of the commission and its subsequent activities that include organising nine specialist tephra-field meetings in seven different countries, numerous conference sessions or workshops, and generating tephra-themed issues of journals/books or specialist internet documents or websites. The commission began to prosper after 1987 when key changes occurred, and it has blossomed further, especially in the past decade or so as an entire new cohort of specialists has emerged alongside new analytical and dating techniques to become a vibrant global group today. We name 29 elected officers involved with COT since 1961 and their roles, and 15 honorary life members. We also document the aims of the commission and conclude by evaluating its legacies and current and future work.

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.

Climatic warming from the last glacial maximum to the current interglacial period was punctuated by a similar to 1300 years long cold period, commonly referred to as the Younger Dryas (YD). Several hypotheses have been proposed for the mechanism triggering the abrupt inception of the YD, including freshwater forcing, an extra-terrestrial impact, and aerosols from volcanic eruptions. Here, we use synchronised sulphate and sulphur records from both Greenland and Antarctic ice cores to reconstruct volcanic forcing between 13,200-12,800 a BPGICC05 (years before 1950 CE on the Greenland Ice Core Chronology 2005; GICC05). This continuous reconstruction of stratospheric sulphur injections highlights a -110-year cluster of four major bipolar volcanic signals alongside several smaller events just prior to the YD inception. The cumulative Northern Hemisphere aerosol burden and radiative forcing from this cluster exceeds the most volcanically active periods during the Common Era, which experienced notable multidecadal scale cooling commonly attributed to volcanic effects. The Laacher See eruption (LSE), recently redated to 13,006 +/- 9 cal a BP, falls within our time window of study and has been proposed as a trigger for the YD but a direct volcanic imprint for the LSE in the Greenland ice cores has thus far proved elusive. Comparison of simulated sulphate deposition for mid- and high-sulphur LSE-type emission scenarios to the ice-core estimated sulphate deposition and interhemispheric asymmetry ratios allows several signals between 13,025 and 12,975 a BPGICC05 to be proposed as plausible candidates for the LSE. The magnitude and persistence of volcanic forcing directly preceding the YD inception highlights the need to consider stratospheric sulphur injections and their radiative forcing in future analyses and climate model experiments used to explore the mechanisms that triggered this or similar abrupt cooling events. (C) 2021 The Authors. Published by Elsevier Ltd.

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.